High Airway Occlusion Pressure Is Associated with Dyspnea and Increased Mortality in Critically Ill Mechanically Ventilated Patients

High Tidal Volume Variability Is Associated With Worse Outcomes in Patients With ARDS

Background: The impact of spontaneous breathing during mechanical ventilation on the outcome of ARDS has yet to be established. This study aimed to evaluate the effect of tidal volume variability on ventilator-free days in mechanically ventilated subjects with ARDS using high-resolution tidal volume data collected through patient monitors. Methods: This single-center, retrospective cohort study included adult subjects with ARDS who received mechanical ventilation in our medical ICU between April 2018 and July 2019. The study subjects' expiratory tidal volume data during the first 7 days of mechanical ventilation were collected every 2 s from the patient monitors. The subjects were divided equally into 3 groups according to the coefficient of variation (CV) of all collected normalized tidal volume values. Results: A total of 108 subjects with ARDS were categorized into the low, intermediate, and high CV groups (each number = 36). Baseline characteristics of the 3 groups were comparable except for a lower PaO2/FIO2 in the low CV group (130 ± 50 mm Hg vs 160 ± 57 mm Hg vs 158 ± 50 mm Hg, P = .03). On average, 222,776 tidal volume data points were collected per subject during the first 7 days of mechanical ventilation. The CVs of tidal volume were 17% ± 3%, 26% ± 2%, and 38% ± 8% in each group, respectively. The number of ventilator-free days was significantly lower in the high CV group than in the intermediate CV group (0 [interquartile range or IQR, 0-2.5] days vs 16 [IQR, 0-21.5] days, P = .004 after Bonferroni correction). After adjusting in the zero-inflated negative binomial model, high CV was significantly associated with fewer ventilator-free days compared with intermediate CV (odds ratio, 11.1, 95% CI [2.3-52.7], P = .002). Conclusions: Based on the high-resolution tidal volume data from the patient monitors, high tidal volume variability during the first 7 days of mechanical ventilation in subjects with ARDS was associated with fewer ventilator-free days.

Dyspnea Among Mechanically Ventilated Patients: A Systematic Review

OBJECTIVES

Dyspnea is a common and distressing symptom; yet, how frequently and intensely mechanically ventilated patients experience dyspnea remains unclear. We performed a systematic review to identify the prevalence and severity of dyspnea in communicative, mechanically ventilated critically ill adults. We also identified factors associated with dyspnea in the short-term and long-term and potential management strategies.

DATA SOURCES

We performed a systematic search of the following databases: MEDLINE, Embase, Cochrane Central Register of Controlled Trials, Web of Science Core Collection, PsycInfo, and CINAHL.

DATA EXTRACTION

Our search strategy used variations of these terms: dyspnea, mechanical ventilation, and critical care. We included prospective observational studies and randomized controlled trials. Two independent reviewers screened citations and extracted data using a predrafted report form to examine dyspnea prevalence and severity, association with short-term and long-term outcomes, and interventions to mitigate dyspnea.

DATA SYNTHESIS

Of 6290 records screened, we included 21 observational studies and 3 randomized controlled trials. We calculated percentages and 95% CIs for prevalence using Stata 17 se. Dyspnea was present in 475 of 1169 communicative, mechanically ventilated patients (40.6%, 95% CI, 37.8-43.5) and was found to be moderate to severe. In the lone study to examine long-term outcomes, dyspnea was associated with posttraumatic stress disorder (PTSD) at 90 days. Interventions to reduce dyspnea included: mechanical threshold inspiratory muscle training, ventilation adjustments, supplemental high-flow nasal cannula, opioids, hyperoxemia, and nonpharmacologic interventions, including music and fan therapy.

CONCLUSIONS

In this systematic review, we found that dyspnea among mechanically ventilated patients is common and moderate to severe in its intensity. Dyspnea is associated with adverse long-term outcomes, including probable PTSD. Strategies to manage, or palliate, dyspnea were identified. Future study is warranted to examine how this information can be incorporated into clinical practice to improve short-term and long-term outcomes.

Monitoring patients with acute respiratory failure during non-invasive respiratory support to minimize harm and identify treatment failure

Non-invasive respiratory support (NRS), including high flow nasal oxygen therapy, continuous positive airway pressure and non-invasive ventilation, is a cornerstone in the management of critically ill patients who develop acute respiratory failure (ARF). Overall, NRS reduces the work of breathing and relieves dyspnea in many patients with ARF, sometimes avoiding the need for intubation and invasive mechanical ventilation with variable efficacy across diverse clinical scenarios. Nonetheless, prolonged exposure to NRS in the presence of sustained high respiratory drive and effort can result in respiratory muscle fatigue, cardiovascular collapse, and impaired oxygen delivery to vital organs, leading to poor outcomes in patients who ultimately fail NRS and require intubation. Assessment of patients' baseline characteristics before starting NRS, close physiological monitoring to evaluate patients' response to respiratory support, adjustment of device settings and interface, and, most importantly, early identification of failure or of paramount importance to avoid the negative consequences of delayed intubation. This review highlights the role of respiratory monitoring across various modalities of NRS in patients with ARF including dyspnea, general respiratory parameters, measures of drive and effort, and lung imaging. It includes technical specificities related to the target population and emphasizes the importance of clinicians' physiological understanding and tailoring clinical decisions to individual patients' needs.

Monitoring effort and respiratory drive in patients with acute respiratory failure

PURPOSE OF REVIEW

Accurate monitoring of respiratory drive and inspiratory effort is crucial for optimizing ventilatory support during acute respiratory failure. This review evaluates current and emerging bedside methods for assessing respiratory drive and effort.

RECENT FINDINGS

While electrical activity of the diaphragm and esophageal pressure remain the reference standards for assessing respiratory drive and effort, their clinical utility is largely limited to research. At the bedside, airway occlusion maneuvers are the most useful tools: P0.1 is a reliable marker of drive and detects abnormal inspiratory efforts, while occlusion pressure (Pocc) may outperform P0.1 in identifying excessive effort. The Pressure-Muscle-Index (PMI) can help detecting insufficient inspiratory effort, though its accuracy depends on obtaining a stable plateau pressure. Other techniques, such as central venous pressure swings (ΔCVP), are promising but require further investigation. Emerging machine learning and artificial intelligence based algorithms could play a pivotal role in automated respiratory monitoring in the near future.

SUMMARY

Although Pes and EAdi remain reference methods, airway occlusion maneuvers are currently the most practical bedside tools for monitoring respiratory drive and effort. Noninvasive alternatives such as ΔCVP deserve further evaluation. Artificial intelligence and machine learning may soon provide automated solutions for bedside monitoring of respiratory drive and effort.

Automatic continuous P0.1 measurements during weaning from mechanical ventilation: a clinical study

BACKGROUND

In critically ill patients, weaning from mechanical ventilation (MV) includes spontaneous breathing trial (SBT) usually followed by a reventilation period in order to recover from the alveolar derecruitement induced by the SBT. The measurement of occlusion pressure during the first 100 ms of an airway occlusion (P0.1) one of the non-invasive tools available for estimating the respiratory drive, is a determinant of patient respiratory effort. This clinical study explores the use of non-invasive continuous monitoring of occlusion pressure automatically calculated by ventilators in the first 100 ms of airway occlusion (P0.1 vent) during SBT and reventilation periods. The study aimed to investigate patient or respirator factors influencing P0.1 vent as well as the association of P0.1 vent values with extubation success or failure.

PATIENTS AND METHODS

This prospective observational study, conducted from February 2022 to April 2023, included adult patients intubated for more than 24 h and screened for extubation weaning. SBTs were performed for one hour with zero pressure support and zero end-expiratory pressure (PS0 ZEEP). Reventilation followed for an hour with pressure support (8-12 cmH2O) and PEEP (5 cmH2O). Data included patient characteristics, ventilator parameters and extubation outcomes.

RESULTS

The study involved 224 measurements from 212 patients, with 157 successful extubations, 46 extubation failures at day 7 and 21 SBT failures. P0.1 vent mean values were significantly higher for extubation failures and SBT failures compared to successful extubations (p < 0.001). Delta P0.1 vent ((P0.1 vent reventilation - P0.1 vent SBT)/ P0.1 vent SBT) was significantly different according to whether extubation was a success or a failure: 0.21 (0.02-0.62) cm H2O vs. P0.1 vent vs. 1.12 (0.54-2.38) cm H2O; p < 0.0001 respectively. Values significantly differed in both the SBT and the reventilation periods whether or not patients had previous ARDS: 1.08 (0.70; 2.02) cmH2O vs. 0.80 (0.54; 1.28) cmH2O respectively (p = 0.003). Noteworthy, P0.1 vent values were influenced by airway humidification systems (0.92 (0.57; 1.54) cmH2O with humidification vs. 1.27 (0.91; 2.24) cmH2O without, p = 0.003).

CONCLUSION

The delta of P0.1vent values between SBT and reventilation are higher for patients who fail extubation, especially for those who had ARDS. While elevated P0.1 vent values were associated with extubation failure, the overlap in values limits its usefulness as a reliable predictor.

[Role of respiratory therapists in weaning patients from invasive mechanical ventilation: a description of their responsibilities from a certified weaning centre]

Respiratory therapists have been trained by the German Respiratory Society (DGP) since 2005. Respiratory therapeutic interventions related to weaning patients from invasive mechanical ventilation are a major focus. Respiratory therapists have been an integral part of the therapeutic team at the Thorax Clinic Heidelberg for more than 10 years. This article describes their tasks and responsibilities in the context of weaning from invasive mechanical ventilation. The acute treatment phase of invasively ventilated patients in the acute intensive care unit and the prolonged weaning phase in the pneumological intensive care unit are presented in chronological order. The therapeutic focus of each phase is presented and described.

Multimodal physiological correlates of dyspnea ratings during breath-holding in healthy humans

INTRODUCTION AND OBJECTIVES

Dyspnea is associated with fear and intense suffering and is often assessed using visual analog scales (VAS) or numerical rating scales (NRS). However, the physiological correlates of such ratings are not well known. Using the voluntary breath-holding model of induced dyspnea, we studied healthy volunteers to investigate the temporal relationship between dyspnea, the neural drive to breathe assessed in terms of involuntary thoracoabdominal movements (ITMs) and neurovegetative responses.

PARTICIPANTS AND METHODS

Twenty-three participants (10 men; median [interquartile range] age 21 [20-21]) performed three consecutive breath-holds with the continuous assessment of dyspnea (urge-to-breathe) using a 10 cm VAS, thoracic and abdominal circumferences measured with piezoelectric belt-mounted transducers, heart rate and heart rate variability (HRV), and galvanic skin response (GSR). Urge-to-breathe VAS at the onset of ITMs (gasping point) was identified visually or algorithmically.

RESULTS

Urge-to-breathe VAS at the end of the breath-hold was 9.7 [8.6-10] cm. Total breath-hold duration was 93 [69-130] s. Urge-to-breathe VAS, ITM, heart rate, HRV, and GSR significantly increased during breath-hold. Urge-to-breathe VAS correlated with the magnitude of the thoracic and abdominal movements (rho = 0.51 and rho = 0.59, respectively, p < 0.001). The urge-to-breathe ratings corresponding with ITM onset were 3.0 [2.0-4.7] cm and 3.0 [1.0-4.0] cm for visual and algorithmic detection, respectively (p = 0.782).

CONCLUSION

An urge-to-breathe VAS of 3 cm (30% of full scale on a 10 cm VAS) corresponds to a physiological turning point during the physiological response to voluntary breath-holding in healthy humans.

Monitoring and modulating respiratory drive in mechanically ventilated patients

PURPOSE OF REVIEW

Respiratory drive is frequently deranged in the ICU, being associated with adverse clinical outcomes. Monitoring and modulating respiratory drive to prevent potentially injurious consequences merits attention. This review gives a general overview of the available monitoring tools and interventions to modulate drive.

RECENT FINDINGS

Airway occlusion pressure (P0.1) is an excellent measure of drive and is displayed on ventilators. Respiratory drive can also be estimated based on the electrical activity of respiratory muscles and measures of respiratory effort; however, high respiratory drive might be present in the context of low effort with neuromuscular weakness. Modulating a deranged drive requires a multifaceted intervention, prioritizing treatment of the underlying cause and adjusting ventilator settings for comfort. Additional tools include changes in PEEP, peak inspiratory flow, fraction of inspired oxygen, and sweep gas flow (in patients receiving extracorporeal life-support). Sedatives and opioids have differential effects on drive according to drug category. Monitoring response to any intervention is warranted and modulating drive should not preclude readiness to wean assessment or delay ventilation liberation.

SUMMARY

Monitoring and modulating respiratory drive are feasible based on physiological principles presented in this review. However, evidence arising from clinical trials will help determine precise thresholds and optimal interventions.

Bedside Assessment of the Respiratory System During Invasive Mechanical Ventilation

Assessing the respiratory system of a patient receiving mechanical ventilation is complex. We provide an overview of an approach at the bedside underpinned by physiology. We discuss the importance of distinguishing between extensive and intensive ventilatory variables. We outline methods to evaluate both passive patients and those making spontaneous respiratory efforts during assisted ventilation. We believe a comprehensive assessment can influence setting mechanical ventilatory support to achieve lung and diaphragm protective ventilation.

Challenges in Transitioning from Controlled to Assisted Ventilation in Acute Respiratory Distress Syndrome (ARDS) Management

Acute respiratory distress syndrome (ARDS) presents significant challenges in critical care, primarily due to its inflammatory nature, which leads to impaired gas exchange and respiratory mechanics. While mechanical ventilation (MV) is essential for patient support, the transition from controlled to assisted ventilation is complex and may be associated with intensive care unit-acquired weakness, ventilator-induced diaphragmatic dysfunction and patient self-inflicted lung injury. This paper explores the multifaceted challenges encountered during this transition, with a focus on respiratory effort, sedation management, and monitoring techniques, and investigates innovative approaches to enhance patient outcomes. The key strategies include optimizing sedation protocols, employing advanced monitoring methods like esophageal pressure measurements, and implementing partial neuromuscular blockade to prevent excessive respiratory effort. We also emphasize the importance of personalized treatment plans and the integration of artificial intelligence to facilitate timely transitions. By highlighting early rehabilitation techniques, continuously assessing the respiratory drive, and fostering collaboration among multidisciplinary teams, clinicians can improve the transition from controlled to assisted MV, ultimately enhancing recovery and long-term respiratory health in patients with ARDS.

Phenotypes based on respiratory drive and effort to identify the risk factors when P0.1 fails to estimate ∆PES in ventilated children

BACKGROUND

Monitoring respiratory effort and drive during mechanical ventilation is needed to deliver lung and diaphragm protection. Esophageal pressure (∆PES) is the gold standard measure of respiratory effort but is not routinely available. Airway occlusion pressure in the first 100 ms of the breath (P0.1) is a readily available surrogate for both respiratory effort and drive but is only modestly correlated with ∆PES in children. We sought to identify risk factors for P0.1 over or underestimating ∆PES in ventilated children.

METHODS

Secondary analysis of physiological data from children and young adults enrolled in a randomized controlled trial testing lung and diaphragm protective ventilation in pediatric acute respiratory distress syndrome (PARDS) (NCT03266016). ∆PES (∆PES-REAL), P0.1 and predicted ∆PES (∆PES-PRED = 5.91*P0.1) were measured daily to identify phenotypes based upon the level of respiratory effort and drive: one passive (no spontaneous breathing), three where ∆PES-REAL and ∆PES-PRED were aligned (low, normal, and high effort and drive), two where ∆PES-REAL and ∆PES-PRED were mismatched (high underestimated effort, and overestimated effort). Logistic regression models were used to identify factors associated with each mismatch phenotype (High underestimated effort, or overestimated effort) as compared to all other spontaneous breathing phenotypes.

RESULTS

We analyzed 953 patient days (222 patients). ∆PES-REAL and ∆PES-PRED were aligned in 536 (77%) of the active patient days. High underestimated effort (n = 119 (12%)) was associated with higher airway resistance (adjusted OR 5.62 (95%CI 2.58, 12.26) per log unit increase, p < 0.001), higher tidal volume (adjusted OR 1.53 (95%CI 1.04, 2.24) per cubic unit increase, p = 0.03), higher opioid use (adjusted OR 2.4 (95%CI 1.12, 5.13, p = 0.024), and lower set ventilator rate (adjusted OR 0.96 (95%CI 0.93, 0.99), p = 0.005). Overestimated effort was rare (n = 37 (4%)) and associated with higher alveolar dead space (adjusted OR 1.05 (95%CI 1.01, 1.09), p = 0.007) and lower respiratory resistance (adjusted OR 0.32 (95%CI 0.13, 0.81), p = 0.017).

CONCLUSIONS

In patients with PARDS, P0.1 commonly underestimated high respiratory effort particularly with high airway resistance, high tidal volume, and high doses of opioids. Future studies are needed to investigate the impact of measures of respiratory effort, drive, and the presence of a mismatch phenotype on clinical outcome.

TRIAL REGISTRATION

NCT03266016; August 23, 2017.

Clinical and Experimental Evidence for Patient Self-Inflicted Lung Injury (P-SILI) and Bedside Monitoring

Patient self-inflicted lung injury (P-SILI) is a major challenge for the ICU physician: although spontaneous breathing is associated with physiological benefits, in patients with acute respiratory distress syndrome (ARDS), the risk of uncontrolled inspiratory effort leading to additional injury needs to be assessed to avoid delayed intubation and increased mortality. In the present review, we analyze the available clinical and experimental evidence supporting the existence of lung injury caused by uncontrolled high inspiratory effort, we discuss the pathophysiological mechanisms by which increased effort causes P-SILI, and, finally, we consider the measurements and interpretation of bedside physiological measures of increased drive that should alert the clinician. The data presented in this review could help to recognize injurious respiratory patterns that may trigger P-SILI and to prevent it.

Respiratory drive: a journey from health to disease

Respiratory drive is defined as the intensity of respiratory centers output during the breath and is primarily affected by cortical and chemical feedback mechanisms. During the involuntary act of breathing, chemical feedback, primarily mediated through CO2, is the main determinant of respiratory drive. Respiratory drive travels through neural pathways to respiratory muscles, which execute the breathing process and generate inspiratory flow (inspiratory flow-generation pathway). In a healthy state, inspiratory flow-generation pathway is intact, and thus respiratory drive is satisfied by the rate of volume increase, expressed by mean inspiratory flow, which in turn determines tidal volume. In this review, we will explain the pathophysiology of altered respiratory drive by analyzing the respiratory centers response to arterial partial pressure of CO2 (PaCO2) changes. Both high and low respiratory drive have been associated with several adverse effects in critically ill patients. Hence, it is crucial to understand what alters the respiratory drive. Changes in respiratory drive can be explained by simultaneously considering the (1) ventilatory demands, as dictated by respiratory centers activity to CO2 (brain curve); (2) actual ventilatory response to CO2 (ventilation curve); and (3) metabolic hyperbola. During critical illness, multiple mechanisms affect the brain and ventilation curves, as well as metabolic hyperbola, leading to considerable alterations in respiratory drive. In critically ill patients the inspiratory flow-generation pathway is invariably compromised at various levels. Consequently, mean inspiratory flow and tidal volume do not correspond to respiratory drive, and at a given PaCO2, the actual ventilation is less than ventilatory demands, creating a dissociation between brain and ventilation curves. Since the metabolic hyperbola is one of the two variables that determine PaCO2 (the other being the ventilation curve), its upward or downward movements increase or decrease respiratory drive, respectively. Mechanical ventilation indirectly influences respiratory drive by modifying PaCO2 levels through alterations in various parameters of the ventilation curve and metabolic hyperbola. Understanding the diverse factors that modulate respiratory drive at the bedside could enhance clinical assessment and the management of both the patient and the ventilator.