Advanced Respiratory Monitoring during Extracorporeal Membrane Oxygenation

Advanced respiratory monitoring encompasses a diverse range of mini- or noninvasive tools used to evaluate various aspects of respiratory function in patients experiencing acute respiratory failure, including those requiring extracorporeal membrane oxygenation (ECMO) support. Among these techniques, key modalities include esophageal pressure measurement (including derived pressures), lung and respiratory muscle ultrasounds, electrical impedance tomography, the monitoring of diaphragm electrical activity, and assessment of flow index. These tools play a critical role in assessing essential parameters such as lung recruitment and overdistention, lung aeration and morphology, ventilation/perfusion distribution, inspiratory effort, respiratory drive, respiratory muscle contraction, and patient-ventilator synchrony. In contrast to conventional methods, advanced respiratory monitoring offers a deeper understanding of pathological changes in lung aeration caused by underlying diseases. Moreover, it allows for meticulous tracking of responses to therapeutic interventions, aiding in the development of personalized respiratory support strategies aimed at preserving lung function and respiratory muscle integrity. The integration of advanced respiratory monitoring represents a significant advancement in the clinical management of acute respiratory failure. It serves as a cornerstone in scenarios where treatment strategies rely on tailored approaches, empowering clinicians to make informed decisions about intervention selection and adjustment. By enabling real-time assessment and modification of respiratory support, advanced monitoring not only optimizes care for patients with acute respiratory distress syndrome but also contributes to improved outcomes and enhanced patient safety.

A novel method to quantify breathing effort from respiratory mechanics and esophageal pressure

Breathing effort is important to quantify to understand mechanisms underlying central and obstructive sleep apnea, respiratory-related arousals, and the timing and effectiveness of invasive or non-invasive mechanically assisted ventilation. Current quantitative methods to evaluate breathing effort rely on inspiratory esophageal or epiglottic pressure swings or changes in diaphragm electromyographic (EMG) activity, where units are problematic to interpret and compare between individuals and to measured ventilation. This paper derives a novel method to quantify breathing effort in units directly comparable to measured ventilation by applying respiratory mechanics first principles to convert continuous transpulmonary pressure measurements into "attempted" airflow expected to have arisen without upper airway obstruction. The method was evaluated using data from eleven subjects undergoing overnight polysomnography, including 6 obese patients with severe obstructive sleep apnea (OSA), including one who also had frequent central events, and 5 healthy-weight controls. Classic respiratory mechanics showed excellent fits of airflow and volume to transpulmonary pressures during wake periods of stable unobstructed breathing (mean ± SD r² = 0.94 ± 0.03), with significantly higher respiratory system resistance in patients compared to healthy controls (11.2 ± 3.3 vs 7.1 ± 1.9 cmH2O·l-1·sec, P=0.032). Subsequent estimates of attempted airflow from transpulmonary pressure changes clearly highlighted periods of acute and prolonged upper airway obstruction, including within the first few breaths following sleep onset in patients. This novel technique provides unique quantitative insights into the complex and dynamically changing inter-relationships between breathing effort and achieved airflow during periods of obstructed breathing in sleep.

Comparison of Laryngeal Mask Airway Seal Between Anesthesiologists and Individuals Without Previous Airway Experience

BACKGROUND

Tracheal intubation is the gold standard for airway management in emergency medicine, but more difficult to apply for inexperienced individuals than laryngeal mask airway (LMA).

OBJECTIVE

The aim of our study was to investigate if inexperienced individuals are able to secure the airway with the help of LMA after a short introduction. A second aim was to evaluate Thiel-fixed specimens against unfixed ones.

METHODS

In a body donor model, LMA application was evaluated between medical students without previous airway experience and anesthesiologists by comparing the sealing of the larynx using a water column applied to the esophagus.

RESULTS

LMAs were successfully applied in 46 out of 55 (83.6%) attempts by medical students and in 30 out of 39 (76.9%) attempts by anesthesiologists. Among medical students, 14.1% of all LMA applications were primarily leaky, compared with 18.8% in anesthesiologists. Esophageal sealing was better in Thiel-fixed specimens (leakage 10.9%) compared with unfixed specimens (leakage 22.9%). Our data showed no significant difference between anesthesiologists and medical students in terms of sealing of LMA. Therefore, we conclude that medical students without previous airway experience can quickly learn to apply LMA sufficiently and thus, achieve aspiration protection similar to anesthesiologists.

CONCLUSION

Medical students without previous airway experience can successfully insert LMAs after a short introduction. Thiel-fixed specimens are suitable for studies as well as for training in LMA application.

Evaluation of Optimal Esophageal Catheter Balloon Inflation Volume in Mechanically Ventilated Children

BACKGROUND

Accuracy of esophageal pressure measured by an air-filled esophageal balloon catheter is dependent on balloon filling volume. However, this has been understudied in mechanically ventilated children. We sought to study the optimal filling volume in children receiving ventilation by using previously reported calibration methods. Secondary objectives included to examine the difference in pressure measurements at individualized optimal filling volume versus a standardized inflation volume and to study if a static hold during calibration is required to identify the optimal filling volume.

METHODS

An incremental inflation calibration procedure was performed in children receiving ventilation, <18 y, instrumented with commercially available catheters (6 or 8 French) who were not breathing spontaneously. The balloon was manually inflated by 0.2 to 1.6 mL (6 French) or 2.6 mL (8 French). Esophageal pressure (Pes) and airway pressure tracings were recorded during the procedure. Data were analyzed offline by using 2 methods: visual determination of filling range with the calculation of the highest difference between expiratory and inspiratory Pes and determination of a correctly filled balloon by calculating the esophageal elastance.

RESULTS

We enrolled 40 subjects with median (interquartile range [IQR]) age 6.8 (2-25) months. The optimal filling volume ranged from 0.2 to 1.2 mL (median [IQR] 0.6 [0.2-1.0] mL) in the subjects with a 6 French catheter and 0.2-2.0 mL (median [IQR] 0.7 [0.5-1.2] mL) for 8 French catheters. Inflating the balloon with 0.6 mL (median computed from the whole cohort) gave an absolute difference in transpulmonary pressure that ranged from -4 to 7 cm H2O compared with the personalized volume. Pes calculated over 5 consecutives breaths differed with a maximum of 1 cm H2O compared to Pes calculated during a single inspiratory hold. The esophageal elastance was correlated with weight, age, and sex.

CONCLUSIONS

The optimal balloon inflation volume was highly variable, which indicated the need for an individual calibration procedure. Pes was not overestimated when an inspiratory hold was not applied.

Esophageal balloon catheter system identification to improve respiratory effort time features and amplitude determination

Objective. Understanding a patient's respiratory effort and mechanics is essential for the provision of individualized care during mechanical ventilation. However, measurement of transpulmonary pressure (the difference between airway and pleural pressures) is not easily performed in practice. While airway pressures are available on most mechanical ventilators, pleural pressures are measured indirectly by an esophageal balloon catheter. In many cases, esophageal pressure readings take other phenomena into account and are not a reliable measure of pleural pressure.Approach.A system identification approach was applied to provide accurate pleural measures from esophageal pressure readings. First, we used a closed pressurized chamber to stimulate an esophageal balloon and model its dynamics. Second, we created a simplified version of an artificial lung and tried the model with different ventilation configurations. For validation, data from 11 patients (five male and six female) were used to estimate respiratory effort profile and patient mechanics.Main results.After correcting the dynamic response of the balloon catheter, the estimates of resistance and compliance and the corresponding respiratory effort waveform were improved when compared with the adjusted quantities in the test bench. The performance of the estimated model was evaluated using the respiratory pause/occlusion maneuver, demonstrating improved agreement between the airway and esophageal pressure waveforms when using the normalized mean squared error metric. Using the corrected muscle pressure waveform, we detected start and peak times 130 ± 50 ms earlier and a peak amplitude 2.04 ± 1.46 cmH2O higher than the corresponding estimates from esophageal catheter readings.Significance.Compensating the acquired measurements with system identification techniques makes the readings more accurate, possibly better portraying the patient's situation for individualization of ventilation therapy.

Pulmonary vascular pressure respiratory swings in COPD and ILD candidates for lung transplantation: Large but different

We analyzed the effect of respiratory swings on interpreting intravascular pulmonary vascular pressures (PVPs) in chronic obstructive pulmonary disease (COPD) and interstitial lung disease (ILD) candidates for lung transplantation (LTx) and the role of the alterations in pulmonary function tests on the dynamic respiratory variations. Twenty-eight consecutive patients were included. All patients underwent a complete hemodynamic study (right atrial, mean pulmonary arterial, and pulmonary arterial occlusion pressures [RAP, mPAP, and PAOP]-) and pulmonary function testing (force vital capacity [FVC], forced expiratory volume in the first second [FEV1], and residual volume [RV]). A subgroup of 10 patients underwent simultaneous esophageal pressure (PES). All hemodynamic parameters and PES were collected during apnea after an unforced expiration (ee) and during spontaneous breathing averaging five respiratory cycles (mrc). The respiratory swing (osc) was estimated as the difference between maximum-minimum values of pressures during the respiratory cycle. Intravascular RAPee, mPAPee, and PAOPee were higher than mrc values (p < 0.05), leading to 11% of pulmonary hypertension (PH) misdiagnosis and 37% of postcapillary PH misclassification. PAOPosc of COPD was higher than ILD patients and RAPosc (p < 0.05). Only PAOPosc correlated with FVC, FEV1, and RV (p < 0.05). ILD PESmrc was lower than COPD (p < 0.05), and it was associated with a significantly higher transmural than intravascular RAPmrc, mPAPmrc, and PAOPmrc. PESmrc was significantly correlated with FVC. Transmural mPAPmrc and PAOPmrc readings determined around 20% of reclassification of the patients compared to ee measurements. Candidates for LTx showed large respiratory swings in PVP, which were correlated with pulmonary function alterations. mrc PVP would be more closely approximated to the true transmural PVP leading to PH reclassification. Adjusting PVP for PES should be considered in COPD and ILD candidates of LTx with severe alterations in pulmonary functional tests and suspicion of a PESmrc far from 0. PES respiratory swings could be different in ILD to COPD patients.

Hiccup-like Contractions in Mechanically Ventilated Patients: Individualized Treatment Guided by Transpulmonary Pressure

Hiccups-like contractions, including hiccups, respiratory myoclonus, and diaphragmatic tremor, refer to involuntary, spasmodic, and inspiratory muscle contractions. They have been repeatedly described in mechanically ventilated patients, especially those with central nervous damage. Nevertheless, their effects on patient-ventilator interaction are largely unknown, and even more overlooked is their contribution to lung and diaphragm injury. We describe, for the first time, how the management of hiccup-like contractions was individualized based on esophageal and transpulmonary pressure measurements in three mechanically ventilated patients. The necessity or not of intervention was determined by the effects of these contractions on arterial blood gases, patient-ventilator synchrony, and lung stress. In addition, esophageal pressure permitted the titration of ventilator settings in a patient with hypoxemia and atelectasis secondary to hiccups and in whom sedatives failed to eliminate the contractions and muscle relaxants were contraindicated. This report highlights the importance of esophageal pressure monitoring in the clinical decision making of hiccup-like contractions in mechanically ventilated patients.

Assessment of Inspiratory Effort in Spontaneously Breathing COVID-19 ARDS Patients Undergoing Helmet CPAP: A Comparison between Esophageal, Transdiaphragmatic and Central Venous Pressure Swing

INTRODUCTION

The clinical features of COVID-19 are highly variable. It has been speculated that the progression across COVID-19 may be triggered by excessive inspiratory drive activation. The aim of the present study was to assess whether the tidal swing in central venous pressure (ΔCVP) is a reliable estimate of inspiratory effort.

METHODS

Thirty critically ill patients with COVID-19 ARDS underwent a PEEP trial (0-5-10 cmH₂O) during helmet CPAP. Esophageal (ΔPes) and transdiaphragmatic (ΔPdi) pressure swings were measured as indices of inspiratory effort. ΔCVP was assessed via a standard venous catheter. A low and a high inspiratory effort were defined as ΔPes ≤ 10 and  >15 cmH2O, respectively.

RESULTS

During the PEEP trial, no significant changes in ΔPes (11 [6-16] vs. 11 [7-15] vs. 12 [8-16] cmH2O, p = 0.652) and in ΔCVP (12 [7-17] vs. 11.5 [7-16] vs. 11.5 [8-15] cmH2O, p = 0.918) were detected. ΔCVP was significantly associated with ΔPes (marginal R² 0.87, p < 0.001). ΔCVP recognized both low (AUC-ROC curve 0.89 [0.84-0.96]) and high inspiratory efforts (AUC-ROC curve 0.98 [0.96-1]).

CONCLUSIONS

ΔCVP is an easily available a reliable surrogate of ΔPes and can detect a low or a high inspiratory effort. This study provides a useful bedside tool to monitor the inspiratory effort of spontaneously breathing COVID-19 patients.

Respiratory effort during noninvasive positive pressure ventilation and continuous positive airway pressure in severe acute viral bronchiolitis

OBJECTIVES

To assess if noninvasive positive pressure ventilation (NIPPV) is associated with a greater reduction in respiratory effort as compared to continuous positive airway pressure (CPAP) during severe acute bronchiolitis, with both supports set either clinically or physiologically.

METHODS

Twenty infants (median [IQR] age 1.2 [0.9; 3.2] months) treated <24 h with noninvasive respiratory support (CPAP Clin, set at 7 cmH₂ O, or NIPPV Clin) for bronchiolitis were included in a prospective single-center crossover study. Esogastric pressures were measured first with the baseline support, then with the other support. For each support, recordings were performed with the clinical setting and a physiological setting (CPAP Phys and NIPPV Phys), aiming at normalising respiratory effort. Patients were then treated with the optimal support. The primary outcome was the greatest reduction in esophageal pressure-time product (PTP_ES /min). Other outcomes included improvement of the other components of the respiratory effort.

RESULTS

NIPPV Clin and Phys were associated with a lower PTP_ES /min (164 [105; 202] and 106 [78; 161] cmH₂ O s/min, respectively) than CPAP Clin (178 [145; 236] cmH₂ O s/min; p = 0.01 and 2 × 10^-4 , respectively). NIPPV Clin and Phys were also associated with a significant reduction of all other markers of respiratory effort as compared to CPAP Clin. PTP_ES /min with NIPPV (Clin or Phys) was not different from PTP_ES /min with CPAP Phys. There was no significant difference between physiological and clinical settings.

CONCLUSION

NIPPV is associated with a significant reduction in respiratory effort as compared to CPAP set at +7 cmH₂ O in infants with severe acute bronchiolitis. CPAP Phys performs as well as NIPPV Clin.

Respiratory Variations of Central Venous Pressure as Indices of Pleural Pressure Swings: A Narrative Review

The measurement of pleural (or intrathoracic) pressure is a key element for a proper setting of mechanical ventilator assistance as both under- and over-assistance may cause detrimental effects on both the lungs and the diaphragm. Esophageal pressure (Pes) is the gold standard tool for such measurements; however, it is invasive and seldom used in daily practice, and easier, bedside-available tools that allow for rapid and continuous monitoring are greatly needed. The tidal swing of central venous pressure (CVP) has long been proposed as a surrogate for pleural pressure (Ppl); however, despite the wide availability of central venous catheters, this variable is very often overlooked in critically ill patients. In the present narrative review, the physiological basis for the use of CVP waveforms to estimate Ppl is presented; the findings of previous and recent papers that addressed this topic are systematically reviewed, and the studies are divided into those reporting positive findings (i.e., CVP was found to be a reliable estimate of Pes or Ppl) and those reporting negative findings. Both the strength and pitfalls of this approach are highlighted, and the current knowledge gaps and direction for future research are delineated.

Respiratory Monitoring During Mechanical Ventilation: The Present and the Future

The increased application of mechanical ventilation, the recognition of its harms and the interest in individualization raised the need for an effective monitoring. An increasing number of monitoring tools and modalities were introduced over the past 2 decades with growing insight into asynchrony, lung and chest wall mechanics, respiratory effort and drive. They should be used in a complementary rather than a standalone way. A sound strategy can guide a reduction in adverse effects like ventilator-induced lung injury, ventilator-induced diaphragm dysfunction, patient-ventilator asynchrony and helps early weaning from the ventilator. However, the diversity, complexity, lack of expertise, and associated cost make formulating the appropriate monitoring strategy a challenge for clinicians. Most often, a big amount of data is fed to the clinicians making interpretation difficult. Therefore, it is fundamental for intensivists to be aware of the principle, advantages, and limits of each tool. This analytic review includes a simplified narrative of the commonly used basic and advanced respiratory monitors along with their limits and future prospective.

Practical Aspects of Esophageal Pressure Monitoring in Patients with Acute Respiratory Distress Syndrome

Esophageal pressure (P_es) monitoring is a minimally invasive advanced respiratory monitoring method with the potential to guide ventilation support management. P_es monitoring enables the separation of lung and chest wall mechanics and estimation of transpulmonary pressure, which is recognized as an important risk factor for lung injury during both spontaneous breathing and mechanical ventilation. Appropriate balloon positioning, calibration, and measurement techniques are important to avoid inaccurate results. Both the approach of using absolute expiratory Pes values and the approach based on tidal Pes difference have shown promising results for ventilation adjustments, with the potential to decrease the risk of ventilator-induced lung injury.

The calibration of esophageal pressure by proper esophageal balloon filling volume: A clinical study

Background

Esophageal pressure (Pes) can be used as a reliable surrogate for pleural pressure, especially in critically ill patients requiring personalized mechanical ventilation strategies. How to choose the proper esophageal balloon filling volume and then find the optimal value of esophageal pressure remains a challenge. The study aimed to assess the feasibility of catheters for Pes monitoring in mechanically ventilated patients.

Materials and methods

Twelve patients under pressure-controlled mechanical ventilation were included in this study. Raw esophageal pressure was recorded at different balloon filling volumes. Then, the P-V curves were determined. V _WORK was the intermediate linear section on the end-expiratory P-V curve, and V _BEST was the filling volume providing the maximum difference between Pes at end-inspiration and end-expiration. The raw value of Pes was recorded, and the calibrated values of Pes were calculated by calculating the esophageal wall pressure (Pew) and esophageal elastance (Ees).

Results

Twenty-four series of Pes measurements were performed. The mean V _MIN and V _MAX were 2.17 ± 0.49 ml (range, 1.0-3.0 ml) and 6.79 ± 0.83 ml (range, 5.0-9.0 ml), respectively, whereas V _BEST was 4.69 ± 0.16 ml (range, 2.0-8.0 ml). Ees was 1.35 ± 0.51 cm H₂O/ml (range, 0.26-2.38 cm H₂O/ml). The estimated Pew at V _BEST was 3.16 ± 2.19 cm H₂O (range, 0-7.97 cm H₂O). Patients with a body mass index (BMI) ≥ 25 kg/m² had a significantly lower V _MAX (5.88 [5.25-6] vs. 7.25 [7-8] ml, p = 0.006) and a significantly lower V _BEST (3.69 [2.5-4.38] vs. 5.19 [4-6] ml, p = 0.036) than patients with a BMI < 25 kg/m². Patients with positive end-expiratory pressure (PEEP) ≥ 10 cm H₂O had a lower V _MIN and V _BEST than patients with PEEP < 10 cm H₂O, P > 0.05. Patients in the supine position had a higher esophageal pressure than those in the prone position with the same balloon filling volume.

Conclusions

Calibration of esophageal pressure to identify the best filling volume of esophageal balloon catheters is feasible. The esophageal pressure can be influenced by BMI, PEEP, and position. It is necessary to titrate the optimal inflation volume again when the PEEP values or the positions change.

Esophageal Pressure Measurement in Acute Hypercapnic Respiratory Failure Due to Severe COPD Exacerbation Requiring NIV-A Pilot Safety Study

Esophageal pressure (Pes) measurements could optimise ventilator parameters in acute respiratory failure (ARF) patients requiring noninvasive ventilation (NIV). Consequently, the objectives of our study were to evaluate the safety and accuracy of applying a Pes measuring protocol in ARF patients with AECOPD under NIV in our respiratory intermediate care unit (RICU). An observational cohort study was undertaken. The negative inspiratory swing of Pes (ΔPes) was measured: in an upright/supine position in the presence/absence of NIV at D1 (day of admission), D3 (3rd day of NIV), and DoD (day of discharge). A digital filter for artefact removal was developed. We included 15 patients. The maximum values for ∆Pes were recorded at admission (mean ∆Pes 23.2 cm H2O) in the supine position. ∆Pes decreased from D1 to D3 (p < 0.05), the change being BMI-dependent (p < 0.01). The addition of NIV decreased ∆Pes at D1 and D3 (p < 0.01). The reduction of ∆Pes was more significant in the supine position at D1 (8.8 cm H2O, p < 0.01). Under NIV, ∆Pes values remained higher in the supine versus upright position. Therefore, the measurement of Pes in AECOPD patients requiring NIV can be safely done in an RICU. Under NIV, ∆Pes reduction is most significant within the first 24 h of admission.

Impact of Esophageal Pressure Measurement on Pulmonary Hypertension Diagnosis in Patients With Obesity

BACKGROUND

Elevated intrathoracic pressure could affect pulmonary vascular pressure measurements and influence pulmonary hypertension (PH) diagnosis and classification. Esophageal pressure (Pes) measurement adjusts for the increase in intrathoracic pressure, better reflecting the pulmonary hemodynamics in patients with obesity.

RESEARCH QUESTION

In individuals with obesity, what is the impact of adjusting pulmonary hemodynamic determinations for Pes on PH diagnosis and classification? Can Pes be estimated by positional or respiratory hemodynamic changes?

STUDY DESIGN AND METHODS

In this prospective cohort study, we included patients with obesity who underwent right heart catheterization and demonstrated elevated pulmonary artery wedge pressure (PAWP; ≥ 12 mm Hg). After placement of an esophageal balloon, we performed pressure determination using an air-filled transducer connected to a regular hemodynamic monitor. We measured pulmonary pressures changes when sitting and the variations during the respiratory cycle.

RESULTS

We included 53 patients (mean ± SD age, 59 ± 12 years; mean ± SD BMI, 44.4 ± 10.2 kg/m2). Supine end-expiratory pressures revealed a mean pulmonary artery pressure of > 20 mm Hg in all patients and a PAWP of >15 mm Hg in most patients (n = 50). The Pes adjustment led to a significant decrease in percentage of patients with postcapillary PH (from 60% to 8%) and combined precapillary and postcapillary PH (from 34% to 11%), at the expense of an increase in percentage of patients with no PH (0% to 23%), isolated precapillary PH (2% to 25%), and undifferentiated PH (4% to 34%).

INTERPRETATION

Adjusting pulmonary hemodynamics for Pes in patients with obesity leads to a pronounced reduction in the number of patients who receive a diagnosis of postcapillary PH. Measuring Pes should be considered in patients with obesity, particularly those with elevated PAWP.

Evaluation of Esophageal Pressures in Mechanically Ventilated Obese Patients

BACKGROUND

Patients who are obese are at risk for developing high pleural pressure, which leads to alveolar collapse. Esophageal pressure (P_es) can be used as a surrogate for pleural pressure and can be used to guide PEEP titration. Although recent clinical data on P_es-guided PEEP has shown no benefit, its utility in the subgroup of patients who are obese has not been studied.

METHODS

The Medical Information Mart for Intensive Care-III critical care database was queried to gather data on P_es in subjects on mechanical ventilation. P_es in obese and non-obese groups were compared, and a subgroup analysis was performed in subjects with class III obesity. Thereafter, empirical and P_es-guided PEEP protocols of a recently published trial were theoretically applied to the obese group and ventilator outcomes were compared.

RESULTS

A total of 105 subjects were included in the study. The average end-expiratory P_es in the obese group was 18.8 ± 5 cm H₂O compared with 16.8 ± 4.8 cm H₂O in the non-obese group (P < .05). If P_es-guided PEEP protocol was to be applied to those in the obese group, then the PEEP setting would be significantly higher than empirical PEEP setting. These findings were accentuated in the subgroup of subjects with class III obesity.

CONCLUSIONS

Individualization of PEEP with P_es guidance may have a role in patients who are obese.

Mandibular Movements are a Reliable Noninvasive Alternative to Esophageal Pressure for Measuring Respiratory Effort in Patients with Sleep Apnea Syndrome

PURPOSE

Differentiation between obstructive and central apneas and hypopneas requires quantitative measurement of respiratory effort (RE) using esophageal pressure (PES), which is rarely implemented. This study investigated whether the sleep mandibular movements (MM) signal recorded with a tri-axial gyroscopic chin sensor (Sunrise, Namur, Belgium) is a reliable surrogate of PES in patients with suspected obstructive sleep apnea (OSA).

PATIENTS AND METHODS

In-laboratory polysomnography (PSG) with PES and concurrent MM monitoring was performed. PSGs were scored manually using AASM 2012 rules. Data blocks (n=8042) were randomly sampled during normal breathing (NB), obstructive or central apnea/hypopnea (OA/OH/CA/CH), respiratory effort-related arousal (RERA), and mixed apnea (MxA). Analyses were evaluation of the similarity and linear correlation between PES and MM using the longest common subsequence (LCSS) algorithm and Pearson's coefficient; description of signal amplitudes; estimation of the marginal effect for crossing from NB to a respiratory disturbance for a given change in MM signal using a mixed linear-regression.

RESULTS

Participants (n=38) had mild to severe OSA (median AH index 28.9/h; median arousal index 23.2/h). MM showed a high level of synchronization with concurrent PES signals. Distribution of MM amplitude differed significantly between event types: median (95% confidence interval) values of 0.60 (0.16-2.43) for CA, 0.83 (0.23-4.71) for CH, 1.93 (0.46-12.43) for MxA, 3.23 (0.72-18.09) for OH, and 6.42 (0.88-26.81) for OA. Mixed regression indicated that crossing from NB to central events would decrease MM signal amplitude by -1.23 (CH) and -2.04 (CA) units, while obstructive events would increase MM amplitude by +3.27 (OH) and +6.79 (OA) units (all p<10^-6).

CONCLUSION

In OSA patients, MM signals facilitated the measurement of specific levels of RE associated with obstructive, central or mixed apneas and/or hypopneas. A high degree of similarity was observed with the PES gold-standard signal.

Esophageal Pressure and Clinical Assessments in the Gastroesophageal Reflux Disease Patients with Laryngopharyngeal Reflux Disease

Laryngopharyngeal reflux disease (LPRD) might be associated with reflux symptoms, and its severity is correlated with the Reflux Symptoms Index. Diagnosis is often challenging because of a lack of accurate diagnostic tools. Although an association between LPRD and gastroesophageal reflux disease (GERD) exists, the extent to which esophageal pressure changes in patients with LPRD with GERD has been unknown. Therefore, this study surveys the clinical assessments and extent of esophageal pressure changes in LRPD patients with various GERD severities, and compares esophageal sphincter pressures between ages, genders, and body mass index (BMI). This observational study assessed patients with LPRD and GERD. High-resolution esophageal manometry was used to gather data pertaining to the area pressure on the upper esophageal sphincter (UES) and lower esophageal sphincter (LES), and the correlation between such pressure and symptom severity was determined. We compared the esophageal pressure of different UES and LES levels in the following categories: gender, age, BMI, and GERD severity. We analyzed correlations between esophageal pressure and clinical assessments among 90 patients with throat globus with laryngitis with LPRD. LPRD was measured using laryngoscopy, and GERD was measured using esophagoscopy and 24 h PH monitoring. There were no significant differences in the clinical assessments among the four grades of GERD. The LPRD patients with serious GERD had a lower UES and LES pressure. The lowest pressure and longer duration of LES and UES were also observed among patients with LPRD of grade D GERD. No significant differences in UES and LES pressures among ages, genders, or BMIs were noted.

Transpulmonary Pressure-Guided Lung-Protective Ventilation Improves Pulmonary Mechanics and Oxygenation Among Obese Subjects on Mechanical Ventilation

BACKGROUND

Transpulmonary pressure (P_L) is used to assess pulmonary mechanics and guide lung-protective mechanical ventilation (LPV). P_L is recommended to individualize LPV settings for patients with high pleural pressures and hypoxemia. We aimed to determine whether P_L-guided LPV settings, pulmonary mechanics, and oxygenation improve and differ from non-P_L-guided LPV among obese patients after 24 h on mechanical ventilation. Secondary outcomes included classification of hypoxemia severity, count of ventilator-free days, ICU length of stay, and overall ICU mortality.

METHODS

This is a retrospective analysis of data. Ventilator settings, pulmonary mechanics, and oxygenation were recorded on the initial day of P_L measurement and 24 h later. P_L-guided LPV targeted inspiratory P_L < 20 cm H₂O and expiratory P_L of 0-6 cm H₂O. Comparisons were made to repeat measurements.

RESULTS

Twenty subjects (13 male) with median age of 49 y, body mass index 47.5 kg/m², and SOFA score of 8 were included in our analysis. Fourteen subjects received care in a medical ICU. P_L measurement occurred 16 h after initiating non-P_L-guided LPV. P_L-guided LPV resulted in higher median PEEP (14 vs 18 cm H₂O, P = .009), expiratory P_L (-3 vs 1 cm H₂O, P = .02), respiratory system compliance (30.7 vs 44.6 mL/cm H₂O, P = .001), and [Formula: see text] (156 vs 240 mm Hg, P = .002) at 24 h. P_L-guided LPV resulted in lower [Formula: see text] (0.53 vs 0.33, P < .001) and lower P_L driving pressure (10 vs 6 cm H₂O, P = .001). Tidal volume (420 vs 435 mL, P = .64) and inspiratory P_L (7 vs 7 cm H₂O, P = .90) were similar. Subjects had a median of 7 ventilator-free days, and median ICU length of stay was 14 d. Three of 20 subjects died within 28 d after ICU admission.

CONCLUSIONS

P_L-guided LPV resulted in higher PEEP, lower [Formula: see text], improved pulmonary mechanics, and greater oxygenation when compared to non-P_L-guided LPV settings in adult obese subjects.

Exaggerated ventilatory drive estimates from epiglottic and esophageal pressure deflections in the presence of airway occlusion

Esophageal and epiglottic pressure deflections are widely used to quantify ventilatory effort during sleep in patients with obstructive sleep apnea (OSA). However, changes in upper airway patency will fundamentally alter pressure gradients across the respiratory system with different airflow and volume-dependent effects on esophageal versus epiglottic pressure. The magnitude of these obstruction effects on ventilatory effort assessed from pressure deflections has not been systematically investigated. This study sought to quantify the direct effect of airway occlusion on esophageal and epiglottic pressure deflections during sleep in patients with OSA compared with predictions based on classic respiratory mechanics. Pneumotachograph airflow and volume, and esophageal, epiglottic, mask, and gastric pressures were measured throughout a nonoccluded breath before and the first occluded breath after repeated external airway occlusions during sleep in 13 patients with OSA on constant positive airway pressure (CPAP). Inspiratory pressure deflections were approximately doubled with epiglottic pressure, and increased by around 40% with esophageal pressure on the occluded compared with the preoccluded breath. Differences in pressure between pre- and occluded breaths showed strong dependence on volume and flow, in line with theoretical models of respiratory mechanics. A relatively simple correction factor could account for these effects to provide more consistent measures of ventilatory effort from pressure, independent from measurement site and changing airflow conditions. These finding have important implications for interpreting ventilatory effort and arousal threshold measurements and for understanding the relationships between underlying ventilatory drive and pressure deflections in the presence of airway obstruction during sleep.NEW & NOTEWORTHY Esophageal and epiglottic pressure deflection measurements are widely used as gold-standard measures of ventilatory effort without consideration of differential obstruction effects between measurement sites. This study is the first to quantify the effect of airway occlusion on pressure recordings during sleep. The findings of substantial acute effects of occlusion itself on pressure deflections are important to consider in the planning, analysis, and interpretation of studies that make inferences regarding inspiratory effort.

Effect of the measurement of the work of breathing on the respiratory outcome of preterms

RATIONALE

There are no validated criteria for the choice of the optimal type of noninvasive respiratory support (NRS) and most appropriate settings in preterms.

METHODS

The work of breathing (WOB) during oxygen (O2) alone, nasal continuous positive pressure (nCPAP) and high flow nasal cannula (HFNC) was compared in preterm babies (23-30 weeks' gestation, "physiological group") needing any type of noninvasive respiratory support ("baseline" NRS) at 4 weeks of life. Babies were thereafter treated with the NRS associated with the greatest reduction in WOB ("optimal NRS"). The respiratory outcome at 36 weeks" gestation of these babies was compared to a "control" group treated with NRS based on standard noninvasive parameters. Preterm babies were prospectively enrolled in 3 centers and randomized into the "physiological" or "control" group.

RESULTS

Thirty babies were randomized. WOB with "baseline" NRS was higher than the "optimal" NRS and the consequent NRS chosen by physicians (p = 0.001). WOB was lower during HFNC than during O2 (p = 0.032) but WOB was comparable between nCPAP and HFNC, and between nCPAP and O2. Notably, WOB was near to normal during spontaneous breathing with O2. Respiratory outcome at 36 week' gestation was comparable between the 2 groups.

CONCLUSION

The optimization of NRS by means of the measurement of WOB in preterms requiring any type of NRS at 4 weeks of life was able to decrease the WOB but had no effect on the clinical outcome at 36 weeks' gestation.

Transcutaneous monitoring of diaphragm activity as a measure of work of breathing in preterm infants

OBJECTIVE

Monitoring work of breathing (WOB) is important to assess the pulmonary condition and adjust respiratory support in preterm infants. Conventional WOB measurement (esophageal pressure, tidal volume) is invasive and we hypothesized that monitoring diaphragm activity could be a noninvasive alternative to estimate WOB. The objective was to determine the correlation between conventional WOB measures and diaphragm activity, in preterm infants.

METHODS

WOB and diaphragm activity, measured with transcutaneous electromyography (dEMG), were simultaneously recorded at different nasal continuous positive airway pressure (nCPAP) levels. During a 30-s recording at each nCPAP level, dEMG parameters, inspiratory WOB (WOB_i ), and pressure time product (PTP_in ) were calculated per breath. The correlation coefficient between WOB- and dEMG-measures was calculated using single breaths and after aggregating all breaths into deciles of incremental WOB_i .

RESULTS

Fifteen preterm infants were included (median gestational age, 28 weeks). Single-breath analysis showed a poor median correlation of 0.27 (interquartile range [IQR], 0.03 to 0.33) and 0.08 (IQR, -0.03 to 0.28), respectively, for WOB_i and PTP_in with peak diaphragmatic activity (dEMG_peak ). A modest median correlation coefficient of 0.65 (IQR, 0.13 to 0.79) and 0.43 (IQR, -0.33 to 0.69) was found for, respectively, WOB_i and PTP_in with dEMG_peak in the aggregated analysis.

CONCLUSION

Diaphragm activity showed a modest correlation with WOB_i and PTP_in in an aggregated analysis. This finding warrants further studies in infants with more significant lung disease.

Role of Positive End-Expiratory Pressure and Regional Transpulmonary Pressure in Asymmetrical Lung Injury

Rationale: Asymmetrical lung injury is a frequent clinical presentation. Regional distribution of Vt and positive end-expiratory pressure (PEEP) could result in hyperinflation of the less-injured lung. The validity of esophageal pressure (Pes) is unknown.Objectives: To compare, in asymmetrical lung injury, Pes with directly measured pleural pressures (Ppl) of both sides and investigate how PEEP impacts ventilation distribution and the regional driving transpulmonary pressure (inspiratory - expiratory).Methods: Fourteen mechanically ventilated pigs with lung injury were studied. One lung was blocked while the contralateral one underwent surfactant lavage and injurious ventilation. Airway pressure and Pes were measured, as was Ppl in the dorsal and ventral pleural space adjacent to each lung. Distribution of ventilation was assessed by electrical impedance tomography. PEEP was studied through decremental steps.Measurements and Results: Ventral and dorsal Ppl were similar between the injured and the noninjured lung across all PEEP levels. Dorsal Ppl and Pes were similar. The driving transpulmonary pressure was similar in the two lungs. Vt distribution between lungs was different at zero end-expiratory pressure (≈70% of Vt going in noninjured lung) owing to different respiratory system compliance (8.3 ml/cm H₂O noninjured lung vs. 3.7 ml/cm H₂O injured lung). PEEP at 10 cm H₂O with transpulmonary pressure around zero homogenized Vt distribution opening the lungs. PEEP ≥16 cm H₂O equalized distribution of Vt but with overdistension for both lungs.Conclusions: Despite asymmetrical lung injury, Ppl between injured and noninjured lungs is equalized and esophageal pressure is a reliable estimate of dorsal Ppl. Driving transpulmonary pressure is similar for both lungs. Vt distribution results from regional respiratory system compliance. Moderate PEEP homogenizes Vt distribution between lungs without generating hyperinflation.

High-Flow Oxygen Therapy in Tracheostomized Subjects With Prolonged Mechanical Ventilation: A Randomized Crossover Physiologic Study

BACKGROUND

High-flow oxygen therapy via tracheostomy (HFT) can be used in tracheostomized patients during ventilator disconnection. The physiologic effects of this technique are unknown. We hypothesized that HFT would reduce inspiratory effort and improve breathing pattern compared to conventional oxygen therapy via T-tube. This study aimed to evaluate the physiologic effects of HFT compared to conventional O₂ in patients with prolonged mechanical ventilation.

METHODS

A randomized crossover physiologic study was conducted in adult tracheostomized patients who experienced temporary periods of ventilator disconnection. Subjects were ventilated with pressure support ventilation (PSV) for 15 min and were then randomly assigned to HFT or conventional O₂ via T-tube for 30 min. After a washout period, subjects were switched to the other system. Esophageal pressure (P_es), breathing frequency, blood pressure, heart rate, [Formula: see text], and transcutaneously measured pressure of carbon dioxide ([Formula: see text]) were recorded. The primary outcome was inspiratory effort as determined by the simplified esophageal pressure-time product (sPTP_es). Secondary outcomes were P_es swing, breathing frequency, heart rate, mean arterial pressure, [Formula: see text], and [Formula: see text] between groups.

RESULTS

Twenty-two subjects were enrolled: sPTP_es per minute was significantly higher with HFT and conventional O₂ compared to PSV (153.5 ± 97.9, 163.5 ± 111.3, and 86.8 ± 51.1 cm H₂O × s/min, respectively, P = .001), but it was not different between HFT and conventional O₂ (P = .72). Breathing frequency increased significantly after switching from PSV to HFT and conventional O₂ (23 ± 4 vs 26 ± 6 and 23 ± 4 vs 27 ± 5 breaths/min, respectively, P = .001). [Formula: see text] was higher with conventional O₂ compared to HFT (P = .02). No differences in [Formula: see text], mean arterial pressure, or heart rate were observed between HFT and conventional O₂.

CONCLUSIONS

Inspiratory effort and breathing frequency increased significantly during unassisted breathing compared to PSV in tracheostomized subjects, but HFT via tracheostomy provided no measurable additional physiologic benefit compared to O₂ therapy via T-tube.

A new noninvasive method for measurement of dynamic lung compliance from fluctuations on photoplethysmography in respiration

Lung compliance is important in interstitial lung disease (ILD). However, the measurement requires placement of an esophageal pressure probe and is therefore not done in routine clinic practice. This study was performed to develop and verify a new noninvasive method for estimation of dynamic lung compliance (Cdyn) with a photoplethysmograph (PPG) of pulse wave represented as the changes of absorbance of green LED for hemoglobin and to examine its usefulness. A system for measuring Cdyn in combination with changes in estimated pleural pressure (Ppl) from the fluctuations on PPG with respiration and lung volume measured simultaneously by spirometry was developed and verified to show correspondence with the estimated Ppl and the esophageal pressure (Pes), estimated Cdyn, and Cdyn measured with an esophageal balloon. Furthermore, the estimated percentage of predicted Cdyn (%Cdyn) was compared among healthy subjects (HS) (n = 33) and patients with chronic obstructive pulmonary disease (COPD) (n = 31) and ILD (n = 30). Both estimated Ppl and Cdyn were significantly correlated with Pes (r = 0.89) and measured Cdyn (r = 0.63), respectively. The estimated %Cdyn in ILD showed significantly lower values than those in HS and COPD. The estimated %Cdyn was significantly related to percentage of predicted vital capacity (VC) (r = 0.57, P < 0.01) and percentage of predicted diffusion capacity of carbon monoxide (Dl_CO) (r = 0.50, P < 0.01) in patients with ILD. These findings suggested that the newly developed noninvasive and convenient method for Cdyn estimation using a combination of PPG and spirometry may be useful for the assessment of lung fibrosis in ILD.NEW & NOTEWORTHY Our newly developed method for measuring dynamic lung compliance (Cdyn) in combination with changes in estimated intrathoracic pressure from fluctuations on photoplethysmography with respiration and lung volume measured simultaneously by spirometry showed good linear regression between the estimated Cdyn and the Cdyn measured with an esophageal balloon, and the estimated percentage of predicted Cdyn (%Cdyn) showed significantly lower values in patients with interstitial lung disease (ILD) than in healthy subjects and chronic obstructive pulmonary disease (COPD) patients and significant correlations with vital capacity and lung diffusion capacity.

Prospective Observational Study to Evaluate the Effect of Different Levels of Positive End-Expiratory Pressure on Lung Mechanics in Patients with and without Acute Respiratory Distress Syndrome

Background: The optimal level of positive end-expiratory pressure is still under debate. There are scare data examining the association of PEEP with transpulmonary pressure (TPP), end-expiratory lung volume (EELV) and intraabdominal pressure in ventilated patients with and without ARDS. Methods: We analyzed lung mechanics in 3 patient groups: group A, patients with ARDS; group B, obese patients (body mass index (BMI) > 30 kg/m²) and group C, a control group. Three levels of PEEP (5, 10, 15 cm H₂O) were used to investigate the consequences for lung mechanics. Results: Fifty patients were included, 22 in group A, 18 in group B (BMI 38 ± 2 kg/m²) and 10 in group C. At baseline, oxygenation showed no differences between the groups. Driving pressure (ΔP) and transpulmonary pressure (ΔP_L) was higher in group B than in groups A and C at a PEEP of 5 cm H₂O (ΔP A: 15 ± 1, B: 18 ± 1, C: 14 ± 1 cm H₂O; ΔP_L A: 10 ± 1, B: 13 ± 1, C: 9 ± 0 cm H₂O). Peak inspiratory pressure (P_insp) rose in all groups as PEEP increased, but the resulting driving pressure and transpulmonary pressure were reduced, whereas EELV increased. Conclusion: Measuring EELV or TPP allows a personalized approach to lung-protective ventilation.

Comparison of pleural and esophageal pressure in supine and prone positions in a porcine model of acute respiratory distress syndrome

Patients with moderate to severe acute respiratory distress syndrome (ARDS) benefit from prone positioning. Although the accuracy of esophageal pressure (Pes) to estimate regional pleural pressure (Ppl) has previously been assessed in the supine position, such data are not available in the prone position in ARDS. In six anesthetized, paralyzed, and mechanically ventilated female pigs, we measured Pes and Ppl into dorsal and ventral parts of the right pleural cavity. Airway pressure (Paw) and flow were measured at the airway opening. Severe ARDS [arterial partial pressure of oxygen ([Formula: see text])/fraction of inspired oxygen ([Formula: see text]) < 100 mmHg at positive end-expiratory pressure (PEEP) of 5 cmH₂O] was induced by surfactant depletion. In supine and prone positions assigned in a random order, PEEP was set to 20, 15, 10, and 5 cmH₂O and static end-expiratory chest wall pressures were measured from Pes (PEEPtot,es) and dorsal (PEEPtot,PplD) and ventral (PEEPtot,PplV) Ppl. The magnitude of the difference between PEEPtot,es and PEEPtot,PplD was similar in each position [-3.6 cmH₂O in supine vs. -3.8 cmH₂O in prone at PEEP 20 cmH₂O (PEEP 20)]. The difference between PEEPtot,es and PEEPtot,PplV became narrower in the prone position (-8.3 cmH₂O supine vs. -3.0 cmH₂O prone at PEEP 20). PEEPtot,PplV was overestimated by Pes in the prone position at higher pressures. The median (1st-3rd quartiles) dorsal-to-ventral Ppl gradient was 4.4 (2.4-6.8) cmH₂O in the supine position and -1.5 (-3.5 to +1.1) cmH₂O in the prone position (P < 0.0001) and marginally influenced by PEEP (P = 0.058). Prone position narrowed end-expiratory dorsal-to-ventral Ppl vertical gradient, likely because of a more even distribution of mechanical forces over the chest wall.NEW & NOTEWORTHY In a porcine model of acute respiratory distress syndrome, we found that static end-expiratory esophageal pressure did not change significantly in prone position compared with supine position at any positive end-expiratory pressure (PEEP) tested between 5 and 20 cmH₂O. Prone position was associated with an increased ventral pleural pressure and reduced end-expiratory dorsal-to-ventral pleural pressure (Ppl) vertical gradient, likely due to a more even distribution of mechanical forces over the chest wall.

Intrathoracic Airway Closure Impacts CO2 Signal and Delivered Ventilation during Cardiopulmonary Resuscitation

RATIONALE

End-tidal CO₂ (EtCO₂) is used to monitor cardiopulmonary resuscitation (CPR), but it can be affected by intrathoracic airway closure. Chest compressions induce oscillations in expired CO₂, and this could reflect variable degrees of airway patency.

OBJECTIVES

To understand the impact of airway closure during CPR, and the relationship between the capnogram shape, airway closure, and delivered ventilation.

METHODS

This study had three parts: 1) a clinical study analyzing capnograms after intubation in patients with out-of-hospital cardiac arrest receiving continuous chest compressions, 2) a bench model, and 3) experiments with human cadavers. For 2 and 3, a constant CO₂ flow was added in the lung to simulate CO₂ production. Capnograms similar to clinical recordings were obtained and different ventilator settings tested. EtCO₂ was compared with alveolar CO₂ (bench). An airway opening index was used to quantify chest compression-induced expired CO₂ oscillations in all three clinical and experimental settings.

MEASUREMENTS AND MAIN RESULTS

A total of 89 patients were analyzed (mean age, 69 ± 15 yr; 23% female; 12% of hospital admission survival): capnograms exhibited various degrees of oscillations, quantified by the opening index. CO₂ value varied considerably across oscillations related to consecutive chest compressions. In bench and cadavers, similar capnograms were reproduced with different degrees of airway closure. Differences in airway patency were associated with huge changes in delivered ventilation. The opening index and delivered ventilation increased with positive end-expiratory pressure, without affecting intrathoracic pressure. Maximal EtCO₂ recorded between ventilator breaths reflected alveolar CO₂ (bench).

CONCLUSIONS

During chest compressions, intrathoracic airway patency greatly affects the delivered ventilation. The expired CO₂ signal can reflect CPR effectiveness but is also dependent on airway patency. The maximal EtCO₂ recorded between consecutive ventilator breaths best reflects alveolar CO₂.

Determinants of the esophageal-pleural pressure relationship in humans

Esophageal pressure has been suggested as adequate surrogate of the pleural pressure. We investigate after lung surgery the determinants of the esophageal and intrathoracic pressures and their differences. The esophageal pressure (through esophageal balloon) and the intrathoracic/pleural pressure (through the chest tube on the surgery side) were measured after surgery in 28 patients immediately after lobectomy or wedge resection. Measurements were made in the nondependent lateral position (without or with ventilation of the operated lung) and in the supine position. In the lateral position with the nondependent lung, collapsed or ventilated, the differences between esophageal and pleural pressure amounted to 4.4 ± 1.6 and 5.1 ± 1.7 cmH₂O. In the supine position, the difference amounted to 7.3 ± 2.8 cmH₂O. In the supine position, the estimated compressive forces on the mediastinum were 10.5 ± 3.1 cmH₂O and on the iso-gravitational pleural plane 3.2 ± 1.8 cmH₂O. A simple model describing the roles of chest, lung, and pneumothorax volume matching on the pleural pressure genesis was developed; modeled pleural pressure = 1.0057 × measured pleural pressure + 0.6592 (r² = 0.8). Whatever the position and the ventilator settings, the esophageal pressure changed in a 1:1 ratio with the changes in pleural pressure. Consequently, chest wall elastance (E_cw) measured by intrathoracic (E_cw = ΔPpl/tidal volume) or esophageal pressure (E_cw = ΔPes/tidal volume) was identical in all the positions we tested. We conclude that esophageal and pleural pressures may be largely different depending on body position (gravitational forces) and lung-chest wall volume matching. Their changes, however, are identical.NEW & NOTEWORTHY Esophageal and pleural pressure changes occur at a 1:1 ratio, fully justifying the use of esophageal pressure to compute the chest wall elastance and the changes in pleural pressure and in lung stress. The absolute value of esophageal and pleural pressures may be largely different, depending on the body position (gravitational forces) and the lung-chest wall volume matching. Therefore, the absolute value of esophageal pressure should not be used as a surrogate of pleural pressure.

Assessment of Work of Breathing in Patients with Acute Exacerbations of Chronic Obstructive Pulmonary Disease

The assessment of the work of breathing (WOB) of patients with acute exacerbations of chronic obstructive pulmonary disease (COPD) is difficult, particularly when the patient first presents with acute hypercapnia and respiratory acidosis. Acute exacerbations of COPD patients are in significant respiratory distress and noninvasive measurements of WOB are easier for the patient to tolerate. Given the interest in using alternative therapies to noninvasive ventilation, such as high flow nasal oxygen therapy or extracorporeal carbon dioxide removal, understanding the physiological changes are key and this includes assessment of WOB. This narrative review considers the role of three different methods of assessing WOB in patients with acute exacerbations of COPD. Esophageal pressure is a very well validated measure of WOB, however the ability of patients with acute exacerbations of COPD to tolerate esophageal tubes is poor. Noninvasive alternative measurements include parasternal electromyography (EMG) and electrical impedance tomography (EIT). EMG is easily applied and is a well validated measure of neural drive but is more likely to be degraded by the electrical environment in intensive care or high dependency. EIT is less well validated as a tool for WOB in COPD but extremely well tolerated by patients. Each of the different methods assess WOB in a different way and have different advantages and disadvantages. For research into therapies treating acute exacerbations of COPD, combinations of EIT, EMG and esophageal pressure are likely to be better than only one of these.

Measurement of Diaphragmatic Electrical Activity by Surface Electromyography in Intubated Subjects and Its Relationship With Inspiratory Effort

BACKGROUND

Quantification of patient effort during spontaneous breathing is important to tailor ventilatory assistance. Because a correlation between inspiratory muscle pressure (P_mus) and electrical activity of the diaphragm (EA_di) has been described, we aimed to assess the reliability of surface electromyography (EMG) of the respiratory muscles for monitoring diaphragm electrical activity and subject effort during assisted ventilation.

METHODS

At a general ICU of a single university-affiliated hospital, we enrolled subjects who were intubated and on pressure support ventilation (PSV) and were on mechanical ventilation for > 48 h. The subjects were studied at 3 levels of pressure support. Airway flow and pressure; esophageal pressure; EA_di; and surface EMG of the diaphragm (surface EA_di), intercostal, and sternocleidomastoid muscles were recorded. Respiratory cycles were sampled for off-line analysis. The P_mus/EA_di index (PEI) was calculated by relying on EA_di and surface EA_di (surface PEI) from an airway pressure drop during end-expiratory occlusions performed every minute.

RESULTS

surface EA_di well correlated with EA_di and P_mus, in particular, after averaging breaths into deciles (R = 0.92 and R = 0.84). When surface PEI was used with surface EA_di, it provided a reliable estimation of P_mus (R = 0.94 in comparison with measured P_mus).

CONCLUSIONS

During assisted mechanical ventilation, EA_di can be reliably monitored by both EA_di and surface EMG. The measurement of P_mus based on the calibration of EA_di was also feasible by the use of surface EMG.

Targeting transpulmonary pressure to prevent ventilator-induced lung injury

Introduction: Transpulmonary pressure (PL) is the pressure distending the lung. This pressure equals the stress which develops into the parenchyma at each insufflation and it depends, for a given airway pressure, on the relationship between the lung and the chest wall elastance: a given stress is associated to a given strain, therefor PL is strictly related to ventilator-induced lung injury (VILI). Insufficient knowledge and increased workload account for its limited use in the clinical setting: indeed, the current recommendations for protective ventilation still rely only on the pressures applied to the respiratory system in total (Plateau pressure), without a direct measurement of the real lung stress. Areas covered: We reviewed the significance, the assessment, the application and the limits of transpulmonary pressure in the clinical setting. Expert opinion: Transpulmonary pressure represents a physiologically sound safety limit for mechanical ventilation that should be measured and targeted at least in the most severe ARDS patients. Targeting transpulmonary pressure means 'personalizing' the ventilatory settings.

Different contributions from lungs and chest wall to respiratory mechanics in mice, rats, and rabbits

Changes in lung mechanics are frequently inferred from intact-chest measures of total respiratory system mechanics without consideration of the chest wall contribution. The participation of lungs and chest wall in respiratory mechanics has not been evaluated systematically in small animals commonly used in respiratory research. Thus, we compared these contributions in intact-chest mice, rats, and rabbits and further characterized the influence of positive end-expiratory pressure (PEEP). Forced oscillation technique was applied to anesthetized mechanically ventilated healthy animals to obtain total respiratory system impedance (Z_rs) at 0, 3, and 6 cmH₂O PEEP levels. Esophageal pressure was measured by a catheter-tip micromanometer to separate Z_rs into pulmonary (Z_L) and chest wall (Z_cw) components. A model containing a frequency-independent Newtonian resistance (R_N), inertance, and a constant-phase tissue damping (G) and elastance (H) was fitted to Z_rs, Z_L, and Z_cw spectra. The contribution of Z_cw to R_N was negligible in all species and PEEP levels studied. However, the participation of Z_cw in G and H was significant in all species and increased significantly with increasing PEEP and animal size (rabbit > rat > mice). Even in mice, the chest wall contribution to G and H was still considerable, reaching 47.0 ± 4.0(SE)% and 32.9 ± 5.9% for G and H, respectively. These findings demonstrate that airway parameters can be assessed from respiratory system mechanical measurements. However, the contribution from the chest wall should be considered when intact-chest measurements are used to estimate lung parenchymal mechanics in small laboratory models (even in mice), particularly at elevated PEEP levels. NEW & NOTEWORTHY In species commonly used in respiratory research (rabbits, rats, mice), esophageal pressure-based estimates revealed negligible contribution from the chest wall to the Newtonian resistance. Conversely, chest wall participation in the viscoelastic tissue mechanical parameters increased with body size (rabbit > rat > mice) and positive end-expiratory pressure, with contribution varying between 30 and 50%, even in mice. These findings demonstrate the potential biasing effects of the chest wall when lung tissue mechanics are inferred from intact-chest measurements in small laboratory animals.

Physiological Effect of Prone Position in Children with Severe Bronchiolitis: A Randomized Cross-Over Study (BRONCHIO-DV)

OBJECTIVE

To assess the effect of the prone position on physiological measures, including inspiratory effort, metabolic cost of breathing, and neural drive to the diaphragm as compared with the supine position in infants with severe bronchiolitis requiring noninvasive ventilation.

STUDY DESIGN

Fourteen infants, median age 33 days (IQR [first and third quartiles], 25-58) were randomized to receive 7 cmH₂O continuous positive airway pressure for 1 hour in the prone position or in the supine position, which was followed by cross-over to the supine position and the prone position for 1 hour, respectively. Flow, esophageal, airway, gastric, and transdiaphragmatic pressures, as well as electrical activity of the diaphragm were simultaneously recorded. The modified Wood clinical asthma score was also assessed.

RESULTS

Median esophageal pressure-time product per minute was significantly lower in the prone position than in the supine position (227 cmH₂O*s/minute [IQR, 156-282] cmH₂O*s/minute vs 353 cmH₂O*s/minute [IQR, 249-386 cmH₂O*s/minute]; P = .048), as were the modified Wood clinical asthma score (P = .033) and electrical activity of the diaphragm (P = .006). The neuromechanical efficiency of the diaphragm, as assessed by transdiaphramagtic pressure to electrical activity of the diaphragm swing ratio, was significantly higher in the prone position than in the supine position (1.1 cmH₂O/µV [IQR, 0.9-1.3 cmH₂O/µV] vs 0.7 cmH₂O/µV [IQR, 0.6-1.2 cmH₂O/µV], respectively; P = .022).

CONCLUSIONS

This study suggests a benefit of the prone position for infants with severe bronchiolitis requiring noninvasive ventilation by significantly decreasing the inspiratory effort and the metabolic cost of breathing. Further studies are needed to evaluate the potential impact of these physiological findings in a larger population.

TRIAL REGISTRATION

Clinicaltrials.gov: NCT02602678.

Should we titrate peep based on end-expiratory transpulmonary pressure?-yes

Ventilator management of patients with acute respiratory distress syndrome (ARDS) has been characterized by implementation of basic physiology principles by minimizing harmful distending pressures and preventing lung derecruitment. Such strategies have led to significant improvements in outcomes. Positive end expiratory pressure (PEEP) is an important part of a lung protective strategy but there is no standardized method to set PEEP level. With widely varying types of lung injury, body habitus and pulmonary mechanics, the use of esophageal manometry has become important for personalization and optimization of mechanical ventilation in patients with ARDS. Esophageal manometry estimates pleural pressures, and can be used to differentiate the chest wall and lung (transpulmonary) contributions to the total respiratory system mechanics. Elevated pleural pressures may result in negative transpulmonary pressures at end expiration, leading to lung collapse. Measuring the esophageal pressures and adjusting PEEP to make transpulmonary pressures positive can decrease atelectasis, derecruitment of lung, and cyclical opening and closing of airways and alveoli, thus optimizing lung mechanics and oxygenation. Although there is some spatial and positional artifact, esophageal pressures in numerous animal and human studies in healthy, obese and critically ill patients appear to be a good estimate for the "effective" pleural pressure. Multiple studies have illustrated the benefit of using esophageal pressures to titrate PEEP in patients with obesity and with ARDS. Esophageal pressure monitoring provides a window into the unique physiology of a patient and helps improve clinical decision making at the bedside.

Can we estimate transpulmonary pressure without an esophageal balloon?-yes

A protective ventilation strategy is based on separation of lung and chest wall mechanics and determination of transpulmonary pressure. So far, this has required esophageal pressure measurement, which is cumbersome, rarely used clinically and associated with lack of consensus on the interpretation of measurements. We have developed an alternative method based on a positive end expiratory pressure (PEEP) step procedure where the PEEP-induced change in end-expiratory lung volume is determined by the ventilator pneumotachograph. In pigs, lung healthy patients and acute lung injury (ALI) patients, it has been verified that the determinants of the change in end-expiratory lung volume following a PEEP change are the size of the PEEP step and the elastic properties of the lung, ∆PEEP × Clung. As a consequence, lung compliance can be calculated as the change in end-expiratory lung volume divided by the change in PEEP and esophageal pressure measurements are not needed. When lung compliance is determined in this way, transpulmonary driving pressure can be calculated on a breath-by-breath basis. As the end-expiratory transpulmonary pressure increases as much as PEEP is increased, it is also possible to determine the end-inspiratory transpulmonary pressure at any PEEP level. Thus, the most crucial factors of ventilator induced lung injury can be determined by a simple PEEP step procedure. The measurement procedure can be repeated with short intervals, which makes it possible to follow the course of the lung disease closely. By the PEEP step procedure we may also obtain information (decision support) on the mechanical consequences of changes in PEEP and tidal volume performed to improve oxygenation and/or carbon dioxide removal.

Should we titrate positive end-expiratory pressure based on an end-expiratory transpulmonary pressure?

Arguments continue to swirl regarding the need for and best method of positive end-expiratory pressure (PEEP) titration. An appropriately conducted decremental method that uses modest peak pressures for the recruiting maneuver (RM), a lung protective tidal excursion, relatively small PEEP increments and appropriate timing intervals is currently the most logical and attractive option, particularly when the esophageal balloon pressure (Pes) is used to calculate transpulmonary driving pressures relevant to the lung. The setting of PEEP by the Pes-guided end-expiratory pressure at the 'polarity transition' point of the transmural end-expiratory pressure is quite relevant to the locale of the esophageal balloon catheter. Its desirability, however, is limited by its tendency to encourage PEEP levels that are higher than most other PEEP titration methods. These Pes-set PEEP values promote higher mean airway pressures and are likely to be unnecessary when small tidal driving pressures are in use. Because high airway pressures increase global lung stress and risk hemodynamic compromise, the Pes-determined PEEP would seem associated with a relatively high hazard to benefit ratio for many patients.

Value of measuring esophageal pressure to evaluate heart-lung interactions-applications for invasive hemodynamic monitoring

Evaluation of intrathoracic pressure is the cornerstone of the understanding of heart-lung interactions, but is not easily feasible at the bedside. Esophageal pressure (P_es) has been shown to be a good surrogate for intrathoracic pressure and can be more easily measured using a small esophageal catheter, but is not routinely employed. It can provide crucial information for the study of heart-lung interactions in both controlled and spontaneous ventilation. This review presents the physiological basis, the technical aspects and the value in clinical practice of the measurement of P_es.

Flow and airway pressure analysis for detecting ineffective effort during mechanical ventilation in neuromuscular patients

Ineffective efforts (IEs) are among the most common types of patient–ventilator asynchrony. The objective of this study is to validate IE detection during expiration using pressure and flow signals, with respiratory effort detection by esophageal pressure (Pes) measurement as the reference, in patients with neuromuscular diseases (NMDs). We included 10 patients diagnosed with chronic respiratory failure related to NMD. Twenty-eight 5-minute recordings of daytime ventilation were studied for IE detection. Standard formulas were used to calculate sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of IE detection using pressure and flow signals compared to Pes measurement. Mean sensitivity and specificity of flow and pressure signal-based IE detection versus Pes measurement were 97.5% ± 5.3% and 91.4% ± 13.7%, respectively. NPV was 98.1% ± 8.2% and PPV was 67.6% ± 33.8%. Spearman’s rank correlation coefficient indicated a moderately significant correlation between frequencies of IEs and controlled cycles (ρ = 0.50 and p = 0.01). Among respiratory cycles, 311 (11.2%) were false-positive IEs overall. Separating false-positive IEs according to their mechanisms, we observed premature cycling in 1.2% of cycles, delayed ventilator triggering in 0.1%, cardiac contraction in 9.2%, and upper airway instability during expiration in 0.3%. Using flow and pressure signals to detect IEs is a simple and rapid method that produces adequate data to support clinical decisions.

Characterization of Respiratory Events in Obstructive Sleep Apnea Using Suprasternal Pressure Monitoring

STUDY OBJECTIVES

In obstructive sleep apnea (OSA) esophageal pressure (Pes) is the gold standard for measurement of respiratory effort, and respiratory inductance plethysmography (RIP) is considered an accepted measurement technique. However, the use of RIP could lead to limited accuracy in certain cases and therefore suprasternal pressure (SSP) monitoring might improve the reliability of OSA diagnosis. We aimed to use SSP for the visual characterization of respiratory events in adults and compared results to those obtained by RIP from polysomnography (PSG).

METHODS

In patients with OSA, a 1-night SSP recording using the PneaVoX sensor (Cidelec, Sainte-Gemmes-sur-Loire, France) was done. In parallel, PSG was performed according to American Academy of Sleep Medicine criteria. A subgroup of patients agreed to have Pes measurement in addition. Characterizations of apneas as obstructive, central, and mixed as well as hypopneas as central and obstructive were done by visual evaluation of SSP, RIP, and Pes in random order by two independent scores (S1 and S2). The sensitivity and specificity of characterization by SSP compared to RIP and to Pes were calculated.

RESULTS

Synchronous recordings of SSP and PSG were analyzed from n = 34 patients with OSA (AHI 34.1 ± 24.2 events/h); 9 of them had synchronized Pes monitoring as well. Interscorer agreement for apnea characterization as obstructive, central, and mixed based on SSP, RIP, and Pes were found, with R² values from 0.91-0.99. The sensitivity of SSP in apnea characterization with reference to RIP (S1/S2) was 91.5%/92.3% for obstructive, 82.7%/76.2% for central, and 87.4%/79.9% for mixed. The sensitivity of SSP in apnea characterization with reference to Pes was (S1/S2) 93.1%/92.1% for obstructive, 80.8%/81.6% for central, and 91.7%/90.8% for mixed. Hypopnea was only classified for the nine patients with Pes.

CONCLUSIONS

This study demonstrated a good agreement in the detection of respiratory effort with the SSP signal using the PneaVoX sensor compared to the RIP belts signals as well as to the Pes signal. These findings were consistently found by two independent scorers. In summary, results suggest that SSP is a reliable signal for the classification of respiratory events and could be used as an additional tool for OSA characterization in clinical practice.

Use of Cardiac Cycle Locating to Minimize the Influence of Cardiac Artifacts on Esophageal Pressure Measurement During Dynamic Occlusion Test

BACKGROUND

The dynamic occlusion test is used to guide balloon catheter placement during esophageal pressure (P_es) monitoring. We introduced a cardiac cycle locating method to attenuate the influence of cardiac artifacts on P_es measurement. The aim was to provide a reliable analytic algorithm for the occlusion test.

METHODS

Esophageal balloon catheters were placed in subjects receiving pressure support ventilation. During balloon position adjustment, end-expiratory occlusion was performed to induce 3 consecutive inspiratory efforts. P_es and airway pressure (P_aw) data were collected for off-line analysis. For each occluded inspiratory effort, the change in P_es (ΔP_es) was plotted against the change in P_aw (ΔP_aw), and the slope of the regression line was calculated. The ΔP_es/ΔP_aw ratio was also measured with the cardiac cycle locating method and peak-to-peak method. Bland-Altman analysis was used to assess the agreement between the ΔP_es/ΔP_aw ratio and the slope. We defined the occlusion test with all fitted slopes for the 3 inspiratory efforts within 0.8 to 1.2 to indicate optimal balloon position; otherwise, the position was deemed non-optimal. Using the slope as the reference, the diagnostic accuracy of the ΔP_es/ΔP_aw ratio in distinguishing the optimal and the non-optimal balloon position was analyzed.

RESULTS

A total of 86 occlusion tests containing 258 inspiratory efforts were collected from 15 subjects. The median (interquartile range) slope of ΔP_es versus ΔP_aw plot was 0.85 (0.76, 0.91). Bias (lower and upper limit of agreement) of ΔP_es/ΔP_aw ratio measured by the cardiac cycle locating method and the peak-to-peak method was 0.02 (-0.13 to 0.16) and 0.06 (-0.18 to 0.31), respectively. Forty-five (52.3%) occlusion tests indicated optimal balloon positions. Compared to the peak-to-peak method, the cardiac cycle locating method was more specific in detecting the non-optimal position.

CONCLUSIONS

The cardiac cycle locating method provided reliable and precise measurement for the occlusion test. This method can accurately detect non-optimal balloon position during catheter adjustment.

Fifty Years of Research in ARDS. Respiratory Mechanics in Acute Respiratory Distress Syndrome

Acute respiratory distress syndrome is a multifactorial lung injury that continues to be associated with high levels of morbidity and mortality. Mechanical ventilation, although lifesaving, is associated with new iatrogenic injury. Current best practice involves the use of small Vt, low plateau and driving pressures, and high levels of positive end-expiratory pressure. Collectively, these interventions are termed "lung-protective ventilation." Recent investigations suggest that individualized measurements of pulmonary mechanical variables rather than population-based ventilation prescriptions may be used to set the ventilator with the potential to improve outcomes beyond those achieved with standard lung protective ventilation. This review outlines the measurement and application of clinically applicable pulmonary mechanical concepts, such as plateau pressures, driving pressure, transpulmonary pressures, stress index, and measurement of strain. In addition, the concept of the "baby lung" and the utility of dynamic in addition to static measures of pulmonary mechanical variables are discussed.

Transpulmonary Pressure: The Importance of Precise Definitions and Limiting Assumptions

Recent studies applying the principles of respiratory mechanics to respiratory disease have used inconsistent and mutually exclusive definitions of the term "transpulmonary pressure." By the traditional definition, transpulmonary pressure is the pressure across the whole lung, including the intrapulmonary airways, (i.e., the pressure difference between the opening to the pulmonary airway and the pleural surface). However, more recently transpulmonary pressure has also been defined as the pressure across only the lung tissue (i.e., the pressure difference between the alveolar space and the pleural surface), traditionally known as the "elastic recoil pressure of the lung." Multiple definitions of the same term, and failure to recognize their underlying assumptions, have led to different interpretations of lung physiology and conclusions about appropriate therapy for patients. It is our view that many current controversies in the physiological interpretation of disease are caused by the lack of consistency in the definitions of these common physiological terms. In this article, we discuss the historical uses of these terms and recent misconceptions that may have resulted when these terms were confused. These misconceptions include assertions that normal pleural pressure must be negative (subatmospheric) and that a pressure in the pleural space may not be substantially positive when a subject is relaxed with an open airway. We urge specificity and uniformity when using physiological terms to define the physical state of the lungs, the chest wall, and the integrated respiratory system.

The Effect of Compartmental Asymmetry on the Monitoring of Pulmonary Mechanics and Lung Volumes

BACKGROUND

Esophageal pressure measurement for computation of transpulmonary pressure (P_tp) has begun to be incorporated into clinical use for evaluating forces across the lungs. Gaps exist in our understanding of how esophageal pressure (and therefore P_tp), a value measured at a single site, responds when respiratory system compartments are asymmetrically affected by whole-lung atelectasis or unilateral injury as well as changes in chest wall compliance. We reasoned that P_tp would track with aerated volume changes as estimated by functional residual capacity (FRC) and tidal volume. We examined this hypothesis in the setting of asymmetric lungs and changes in intra-abdominal pressure.

METHODS

This study was conducted in the animal laboratory of a university-affiliated hospital. Models of unilateral atelectasis and unilateral and bilateral lung injury exposed to intra-abdominal hypertension (IAH) in 10 deeply sedated mechanically ventilated swine. Atelectasis was created by balloon occlusion of the left main bronchus. Unilateral lung injury was induced by saline lavage of isolated right lung. Diffuse lung injury was induced by saline lavage of both lungs. The peritoneum was insufflated with air to create a model of pressure-regulated IAH. We measured esophageal pressures, airway pressures, FRC by gas dilution, and oxygenation.

RESULTS

FRC was reduced by IAH in normal lungs (P < .001) and both asymmetric lung pathologies (P < .001). P_tp at end-expiration was decreased by IAH in bilateral (P = .001) and unilateral lung injury (P = .003) as well as unilateral atelectasis (P = .019). In the setting of both lung injury models, end-expiratory P_tp showed a moderate correlation in tracking with FRC.

CONCLUSIONS

P_tp tracks with aerated lung volume in the setting of thoracic asymmetry and changes in intra-abdominal pressure. However, used alone, it cannot distinguish the relative contributions of air-space distention and recruitment of lung units.

Correcting the dynamic response of a commercial esophageal balloon-catheter

It is generally recommended that an esophageal balloon-catheter possess an adequate frequency response up to 15 Hz, such that parameters of respiratory mechanics may be quantified with precision. In our experience, however, we have observed that some commercially available systems do not display an ideal frequency response (<8-10 Hz). We therefore investigated whether the poor frequency response of a commercially available esophageal catheter may be adequately compensated using two numerical techniques: 1) an exponential model correction, and 2) Wiener deconvolution. These two numerical techniques were performed on a commercial balloon-catheter interfaced with 0, 1, and 2 lengths of extension tubing (90 cm each), referred to as configurations L0, L90, and L180, respectively. The frequency response of the balloon-catheter in these configurations was assessed by empirical transfer function analysis, and its "working" range was defined as the frequency beyond which more than 5% amplitude and/or phase distortion was observed. The working frequency range of the uncorrected balloon-catheter extended up to only 10 Hz for L0, and progressively worsened with additional tubing length (L90 = 3 Hz, L180 = 2 Hz). Although both numerical methods of correction adequately enhanced the working frequency range of the balloon-catheter to beyond 25 Hz for all length configurations (L0, L90, and L180), Wiener deconvolution consistently provided more accurate corrections. Our data indicate that Wiener deconvolution provides a superior correction of the balloon-catheter's dynamic response, and is relatively more robust to extensions in catheter tube length compared with the exponential correction method.

Acute respiratory distress syndrome: Pulmonary and extrapulmonary not so similar

Acute respiratory distress syndrome (ARDS) is characterized by acute onset respiratory failure with bilateral pulmonary infiltrates and hypoxemia. Current evidence suggests different respiratory mechanics in pulmonary ARDS (ARDSp) and extrapulmonary ARDS (ARDSexp) with disproportionate decrease in lung compliance in the former and chest wall compliance in the latter. Herein, we report two patients of ARDS, one each with ARDSp and ARDSexp that were managed using real-time esophageal pressure monitoring using the AVEA ventilator to tailor the ventilatory strategy.

Transpulmonary pressure monitoring during mechanical ventilation: a bench-to-bedside review

Different ventilation strategies have been suggested in the past in patients with acute respiratory distress syndrome (ARDS). Airway pressure monitoring alone is inadequate to assure optimal ventilatory support in ARDS patients. The assessment of transpulmonary pressure (PTP) can help clinicians to tailor mechanical ventilation to the individual patient needs. Transpulmonary pressure monitoring, defined as airway pressure (Paw) minus intrathoracic pressure (ITP), provides essential information about chest wall mechanics and its effects on the respiratory system and lung mechanics. The positioning of an esophageal catheter is required to measure the esophageal pressure (Peso), which is clinically used as a surrogate for ITP or pleural pressure (Ppl), and calculates the transpulmonary pressure. The benefits of such a ventilation approach are avoiding excessive lung stress and individualizing the positive end-expiratory pressure (PEEP) setting. The aim is to prevent over-distention of alveoli and the cyclic recruitment/derecruitment or shear stress of lung parenchyma, mechanisms associated with ventilator-induced lung injury (VILI). Knowledge of the real lung distending pressure, i.e. the transpulmonary pressure, has shown to be useful in both controlled and assisted mechanical ventilation. In the latter ventilator modes, Peso measurement allows one to assess a patient's respiratory effort, patient-ventilator asynchrony, intrinsic PEEP and the calculation of work of breathing. Conditions that have an impact on Peso, such as abdominal hypertension, will also be discussed briefly.

The effect of high flow nasal cannula therapy on the work of breathing in infants with bronchiolitis

The main physiological impact of high flow nasal cannula (HFNC) therapy is presumed to be a decrease in work of breathing (WOB). To assess this, diaphragmatic electrical activity and esophageal pressure changes were measured off then on HFNC delivered at 2 L/kg/min, in 14 infants with bronchiolitis and 14 cardiac infants. Electrical activity of the diaphragm (Edi) was measured using an Edi catheter with calculations of signal peak (EdiMAX ) and amplitude (EdiAMPL ). Pressure-rate and pressure-time products (PRP, PTP) were calculated from analyses of esophageal pressure. Changes in end-expiratory lung volume were measured using respiratory inductance plethysmography (RIPEEL ). The EdiMAX and EdiAMPL were significantly higher in infants with bronchiolitis than in cardiac infants (P < 0.05). Within the bronchiolitis group, both were significantly reduced between HFNC states from 27.9 µV [20.4, 35.4] to 21.0 µV [14.8, 27.2] and from 25.1 µV [18.0, 32.2] to 19.2 µV [13.3, 25.1], respectively (mean, 95% CI, P < 0.05). A less prominent offload of the diaphragm was observed in cardiac infants (P < 0.05). WOB decreased in both groups with a significant reduction of PRP and PTP (P < 0.05). RIPEEL increased significantly in bronchiolitis only (P < 0.05). HFNC offloads the diaphragm and reduces the WOB in bronchiolitis. A similar effect was demonstrated in cardiac infants, a group without signs of airway-obstruction.