Pathophysiologic basis of acute respiratory distress in patients who fail a trial of weaning from mechanical ventilation

Respiratory effort in mechanical ventilation weaning Prediction: An observational, case-control study

BACKGROUND

The diaphragm is crucial for ventilator weaning, but its specific impact on weaning indicators needs further clarification. This study investigated the variability in weaning outcomes across different diaphragm function populations and the value of respiratory drive and inspiratory effort in weaning.

METHODS

This observational case-control study enrolled patients on mechanical ventilation for more than 48 h and completed a 30-minute spontaneous breathing trial (SBT) with pressure-support ventilation for the first time. After the SBT, airway pressure at 100 ms during occlusion (P0.1), inspiratory effort, and diaphragmatic ultrasound were evaluated to predict weaning outcomes. Weaning failure was defined as re-intubation within 48 h of weaning, the need for therapeutic non-invasive ventilation, or death.

RESULTS

68 patients with a mean age of 63.21 ± 15.15 years were included. In patients with diaphragm thickness (DT) ≥ 2 mm, P0.1 (P=0.002), pressure-muscle index (PMI) (P=0.012), and occluded expiratory airway pressure swing (ΔPocc) (P=0.030) were significantly higher in those who failed weaning. Conversely, for patients with DT<2 mm, PMI (P=0.003) and ΔPocc (P=0.002) were lower in the weaning failure group. Additionally, within the DT≥2 mm group, P0.1 demonstrated a higher area under the curve (AUC) for weaning prediction (0.889 vs. 0.739) compared to those with DT<2 mm.

CONCLUSIONS

PMI and ΔPocc are predictive of weaning outcomes in patients with diaphragm thickness ≥ 2 mm, where the assessment value of P0.1 is notably higher. Diaphragm function significantly influences the accuracy of weaning predictions based on respiratory drive and inspiratory effort.

IMPLICATIONS FOR CLINICAL PRACTICE

Our findings indicate that the effectiveness of respiratory drive and inspiratory effort in predicting successful weaning from mechanical ventilation may vary across different patient populations. Diaphragm function plays a crucial role in weaning assessments, particularly when using P0.1, the pressure-muscle index (PMI), and occluded expiratory airway pressure swing (ΔPocc).

Mechanical power density, spontaneous breathing indexes, and prolonged weaning failure: a prospective cohort study

A prospective observational study comparing mechanical power density (MP normalized to dynamic compliance) with traditional spontaneous breathing indexes (e.g., predicted body weight normalized tidal volume [VT/PBW], rapid shallow breathing index [RSBI], or the integrative weaning index [IWI]) for predicting prolonged weaning failure in 140 tracheotomized patients. We assessed the diagnostic accuracy of these indexes at the start and end of the weaning procedure using ROC curve analysis, expressed as the area under the receiver operating characteristic curve (AUROC). Weaning failure occurred in 41 out of 140 patients (29%), demonstrating significantly higher MP density (6156 cmH2O2/min [4402-7910] vs. 3004 cmH2O2/min [2153-3917], P < 0.01), lower spontaneous VT/PBW (5.8 mL*kg-1 [4.8-6.8] vs. 6.6 mL*kg-1 [5.7-7.9], P < 0.01) higher RSBI (68 min-1*L-1 [44-91] vs. 55 min-1*L-1 [41-76], P < 0.01) and lower IWI (41 L2/cmH2O*%*min*10-3 [25-72] vs. 71 L2/cmH2O*%*min*10-3 [50-106], P < 0.01) and at the end of weaning. MP density was more accurate at predicting weaning failures (AUROC 0.91 [95%CI 0.84-0.95]) than VT/PBW (0.67 [0.58-0.74]), RSBI (0.62 [0.53-0.70]), or IWI (0.73 [0.65-0.80]), and may help clinicians in identifying patients at high risk for long-term ventilator dependency.

Central venous pressure waveform analysis during sleep/rest: a novel approach to enhance intensive care unit post-extubation monitoring of extubation failure

This pilot study aimed to investigate the relation between cardio-respiratory parameters derived from Central Venous Pressure (CVP) waveform and Extubation Failure (EF) in mechanically ventilated ICU patients during post-extubation period. This study also proposes a new methodology for analysing these parameters during rest/sleep periods to try to improve the identification of EF. We conducted a prospective observational study, computing CVP-derived parameters including breathing effort, spectral analyses, and entropy in twenty critically ill patients post-extubation. The Dynamic Warping Index (DWi) was calculated from the respiratory component extracted from the CVP signal to identify rest/sleep states. The obtained parameters from EF patients and patients without EF were compared both during arbitrary periods and during reduced DWi (rest/sleep). We have analysed data from twenty patients of which nine experienced EF. Our findings may suggest significantly increased respiratory effort in EF patients compared to those successfully extubated. Our study also suggests the occurrence of significant change in the frequency dispersion of the cardiac signal component. We also identified a possible improvement in the differentiation between the two groups of patients when assessed during rest/sleep states. Although with caveats regarding the sample size, the results of this pilot study may suggest that CVP-derived cardio-respiratory parameters are valuable for monitoring respiratory failure during post-extubation, which could aid in managing non-invasive interventions and possibly reduce the incidence of EF. Our findings also indicate the possible importance of considering sleep/rest state when assessing cardio-respiratory parameters, which could enhance respiratory failure detection/monitoring.

Expiratory Muscle Activity Counteracts Positive End-Expiratory Pressure and Is Associated with Fentanyl Dose in Patients with Acute Respiratory Distress Syndrome

Rationale: Hypoxemia during mechanical ventilation might be worsened by expiratory muscle activity, which reduces end-expiratory lung volume through lung collapse. A proposed mechanism of benefit of neuromuscular blockade in acute respiratory distress syndrome (ARDS) is the abolition of expiratory efforts. This may contribute to the restoration of lung volumes. The prevalence of this phenomenon, however, is unknown. Objectives: To investigate the incidence and amount of end-expiratory lung impedance (EELI) increase after the administration of neuromuscular blocking agents (NMBAs), clinical factors associated with this phenomenon, its impact on regional lung ventilation, and any association with changes in pleural pressure. Methods: We included mechanically ventilated patients with ARDS monitored with electrical impedance tomography (EIT) who received NMBAs in one of two centers. We measured changes in EELI, a surrogate for end-expiratory lung volume, before and after NMBA administration. In an additional 10 patients, we investigated the characteristic signatures of expiratory muscle activity depicted by EIT and esophageal catheters simultaneously. Clinical factors associated with EELI changes were assessed. Measurements and Main Results: We included 46 patients, half of whom showed an increase in EELI of >10% of the corresponding Vt (46.2%; IQR, 23.9-60.9%). The degree of EELI increase correlated positively with fentanyl dosage and negatively with changes in end-expiratory pleural pressures. This suggests that expiratory muscle activity might exert strong counter-effects against positive end-expiratory pressure that are possibly aggravated by fentanyl. Conclusions: Administration of NMBAs during EIT monitoring revealed activity of expiratory muscles in half of patients with ARDS. The resultant increase in EELI had a dose-response relationship with fentanyl dosage. This suggests a potential side effect of fentanyl during protective ventilation.

Setting positive end-expiratory pressure in the severely obstructive patient

PURPOSE OF REVIEW

The response to positive end-expiratory pressure (PEEP) in patients with chronic obstructive pulmonary disease (COPD) requiring mechanical ventilation depends on the underlying pathophysiology. This review focuses on the pathophysiology of COPD, especially intrinsic PEEP (PEEPi) and its consequences, and the benefits of applying external PEEP during assisted ventilation when PEEPi is present.

RECENT FINDINGS

The presence of expiratory airflow limitation and increased airway resistance promotes the development of dynamic hyperinflation in patients with COPD during acute respiratory failure. Dynamic hyperinflation and the associated development of PEEPi increases work of breathing and contributes to ineffective triggering of the ventilator. In the presence of airflow limitation, application of external PEEP during patient-triggered ventilation has been shown to reduce inspiratory effort, facilitate ventilatory triggering and enhance patient-ventilator interaction. To minimize the risk of hyperinflation, it is advisable to limit the level of external PEEP during assisted ventilation after optimization of ventilator settings to about 70% of the level of PEEPi (measured during passive ventilation).

SUMMARY

In patients with COPD and dynamic hyperinflation receiving assisted mechanical ventilation, the application of low levels of external PEEP can minimize work of breathing, facilitate ventilator triggering and improve patient-ventilator interaction.

The Neuromechanics of Inspiratory Muscles in Mechanical Ventilation Liberation Success and Failure

BACKGROUND

Assessing the neuromechanical coupling of inspiratory muscles during mechanical ventilation (MV) could reveal the physiological mechanism of MV failure. This study examined the respiratory neuromechanical characteristics between MV liberation success and failure.

METHODS

This is an observational prospective study that included patients during their ventilator liberation process. Assessment of surface electromyography (sEMG) of inspiratory muscles, including the diaphragm and extra-diaphragmatic (scalene, sternocleidomastoid, and parasternal) muscles, was performed 15 minutes after the initiation of spontaneous breathing trials. Neuromechanical efficiency of the diaphragm (NMEDia) and extra-diaphragmatic muscles (NMEExtra) were compared in patients who were successfully liberated from MV with those who failed MV liberation within 72 hours after extubation.

RESULTS

A total of 45 patients were enrolled and 28 were female (67%). The sample median age was 63 (IQR 47, 69) years old. One-third of patients failed MV liberation within 72 hours of their spontaneous breathing trials (SBTs). NMEDia was significantly lower in patients who failed MV liberation with a root mean square of (M 0.27), (IQR 0.21, 0.37) compared with (M 0.371), (IQR 0.3, 0.631) for the success group (p=0.0222). The area under the curve for NMEDia was lower in the failure group (M 0.270), (IQR 0.160, 0.370) and (M 0.485), (IQR 0.280, 0.683) for the success group (p=0.024). However, NMEExtra was not statistically different between the two groups.

CONCLUSION

Reduced NMEDia is a predictor of MV liberation failure. NMEExtra was not a major contributor to MV liberation outcomes. Further studies should assess the performance of inspiratory muscles NME indices to predict MV liberation outcomes.

Automatic tube compensation for liberation from prolonged mechanical ventilation in tracheostomized patients: A retrospective analysis

BACKGROUND

To analyze the predictability of an automatic tube compensation (ATC) screening test compared with the conventional direct liberation test performed before continuous oxygen support for MV liberation.

METHODS

This retrospective study analyzed tracheostomized patients with prolonged MV in a weaning unit of a medical center in Taiwan. In March 2020, a four-day ATC test to screen patient eligibility for ventilator liberation was implemented, intended to replace the direct liberation test. We compared the predictive accuracy of these two screening methods on the relevant outcomes in the two years before and one year after the implementation of this policy.

RESULTS

Of the 403 cases, 246 (61%) and 157 (39%) received direct liberation and ATC screening tests, respectively. These two groups had similar outcomes: successful weaning upon leaving the Respiratory Care Center (RCC), success on day 100 of MV, success at hospital discharge, and in-hospital survival. Receiver operating characteristic curve analysis showed that the ATC screening test had better predictive ability than the direct liberation test for RCC weaning, discharge weaning, 100-day weaning, and in-hospital survival.

CONCLUSION

This closed-circuit ATC screening test before ventilator liberation is a feasible and valuable method for screening PMV patients undergoing ventilator liberation in the pandemic era. Its predictability for a comparison with the open-circuit oxygen test requires further investigation.

Development of a Machine Learning Model for Predicting Weaning Outcomes Based Solely on Continuous Ventilator Parameters during Spontaneous Breathing Trials

Discontinuing mechanical ventilation remains challenging. We developed a machine learning model to predict weaning outcomes using only continuous monitoring parameters obtained from ventilators during spontaneous breathing trials (SBTs). Patients who received mechanical ventilation in the medical intensive care unit at a tertiary university hospital from 2019-2021 were included in this study. During the SBTs, three waveforms and 25 numerical data were collected as input variables. The proposed convolutional neural network (CNN)-based weaning prediction model extracts features from input data with diverse lengths. Among 138 enrolled patients, 35 (25.4%) experienced weaning failure. The dataset was randomly divided into training and test sets (8:2 ratio). The area under the receiver operating characteristic curve for weaning success by the prediction model was 0.912 (95% confidence interval [CI], 0.795-1.000), with an area under the precision-recall curve of 0.767 (95% CI, 0.434-0.983). Furthermore, we used gradient-weighted class activation mapping technology to provide visual explanations of the model's prediction, highlighting influential features. This tool can assist medical staff by providing intuitive information regarding readiness for extubation without requiring any additional data collection other than SBT data. The proposed predictive model can assist clinicians in making ventilator weaning decisions in real time, thereby improving patient outcomes.

Interventions Relieving Dyspnea in Intubated Patients Show Responsiveness of the Mechanical Ventilation-Respiratory Distress Observation Scale

Rationale: Breathing difficulties are highly stressful. In critically ill patients, they are associated with an increased risk of posttraumatic manifestations. Dyspnea, the corresponding symptom, cannot be directly assessed in noncommunicative patients. This difficulty can be circumvented using observation scales such as the mechanical ventilation-respiratory distress observation scale (MV-RDOS). Objective: To investigate the performance and responsiveness of the MV-RDOS to infer dyspnea in noncommunicative intubated patients. Methods: Communicative and noncommunicative patients exhibiting breathing difficulties under mechanical ventilation were prospectively included and assessed using a dyspnea visual analog scale, MV-RDOS, EMG activity of alae nasi and parasternal intercostals, and EEG signatures of respiratory-related cortical activation (preinspiratory potentials). Inspiratory-muscle EMG and preinspiratory cortical activities are surrogates of dyspnea. Assessments were conducted at baseline, after adjustment of ventilator settings, and, in some cases, after morphine administration. Measurements and Main Results: Fifty patients (age, 67 [(interquartile interval [IQR]), 61-76] yr; Simplified Acute Physiology Score II, 52 [IQR, 35-62]) were included, 25 of whom were noncommunicative. Relief occurred in 25 (50%) patients after ventilator adjustments and in 21 additional patients after morphine administration. In noncommunicative patients, MV-RDOS score decreased from 5.5 (IQR, 4.2-6.6) at baseline to 4.2 (IQR, 2.1-4.7; P < 0.001) after ventilator adjustments and 2.5 (IQR, 2.1-4.2; P = 0.024) after morphine administration. MV-RDOS and alae nasi/parasternal EMG activities were positively correlated (ρ = 0.41 and 0.37, respectively). MV-RDOS scores were higher in patients with EEG preinspiratory potentials (4.9 [IQR, 4.2-6.3] vs. 4.0 [IQR, 2.1-4.9]; P = 0.002). Conclusions: The MV-RDOS seems able to detect and monitor respiratory symptoms reasonably well in noncommunicative intubated patients. Clinical trial registered with www.clinicaltrials.gov (NCT02801838).

The oesophageal balloon for respiratory monitoring in ventilated patients: updated clinical review and practical aspects

There is a well-recognised importance for personalising mechanical ventilation settings to protect the lungs and the diaphragm for each individual patient. Measurement of oesophageal pressure (P oes) as an estimate of pleural pressure allows assessment of partitioned respiratory mechanics and quantification of lung stress, which helps our understanding of the patient's respiratory physiology and could guide individualisation of ventilator settings. Oesophageal manometry also allows breathing effort quantification, which could contribute to improving settings during assisted ventilation and mechanical ventilation weaning. In parallel with technological improvements, P oes monitoring is now available for daily clinical practice. This review provides a fundamental understanding of the relevant physiological concepts that can be assessed using P oes measurements, both during spontaneous breathing and mechanical ventilation. We also present a practical approach for implementing oesophageal manometry at the bedside. While more clinical data are awaited to confirm the benefits of P oes-guided mechanical ventilation and to determine optimal targets under different conditions, we discuss potential practical approaches, including positive end-expiratory pressure setting in controlled ventilation and assessment of inspiratory effort during assisted modes.

Managing respiratory muscle weakness during weaning from invasive ventilation

Weaning is a critical stage of an intensive care unit (ICU) stay, in which the respiratory muscles play a major role. Weakness of the respiratory muscles, which is associated with significant morbidity in the ICU, is not limited to atrophy and subsequent dysfunction of the diaphragm; the extradiaphragmatic inspiratory and expiratory muscles also play important parts. In addition to the well-established deleterious effect of mechanical ventilation on the respiratory muscles, other risk factors such as sepsis may be involved. Weakness of the respiratory muscles can be suspected visually in a patient with paradoxical movement of the abdominal compartment. Measurement of maximal inspiratory pressure is the simplest way to assess respiratory muscle function, but it does not specifically take the diaphragm into account. A cut-off value of -30 cmH2O could identify patients at risk for prolonged ventilatory weaning; however, ultrasound may be better for assessing respiratory muscle function in the ICU. Although diaphragm dysfunction has been associated with weaning failure, this diagnosis should not discourage clinicians from performing spontaneous breathing trials and considering extubation. Recent therapeutic developments aimed at preserving or restoring respiratory muscle function are promising.

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.

High-Flow Versus VenturiMask Oxygen Therapy to Prevent Reintubation in Hypoxemic Patients after Extubation: A Multicenter Randomized Clinical Trial

Rationale: When compared with VenturiMask after extubation, high-flow nasal oxygen provides physiological advantages. Objectives: To establish whether high-flow oxygen prevents endotracheal reintubation in hypoxemic patients after extubation, compared with VenturiMask. Methods: In this multicenter randomized trial, 494 patients exhibiting Pa_O2:Fi_O2 ratio ⩽ 300 mm Hg after extubation were randomly assigned to receive high-flow or VenturiMask oxygen, with the possibility to apply rescue noninvasive ventilation before reintubation. High-flow use in the VenturiMask group was not permitted. Measurements and Main Results: The primary outcome was the rate of reintubation within 72 hours according to predefined criteria, which were validated a posteriori by an independent adjudication committee. Main secondary outcomes included reintubation rate at 28 days and the need for rescue noninvasive ventilation according to predefined criteria. After intubation criteria validation (n = 492 patients), 32 patients (13%) in the high-flow group and 27 patients (11%) in the VenturiMask group required reintubation at 72 hours (unadjusted odds ratio, 1.26 [95% confidence interval (CI), 0.70-2.26]; P = 0.49). At 28 days, the rate of reintubation was 21% in the high-flow group and 23% in the VenturiMask group (adjusted hazard ratio, 0.89 [95% CI, 0.60-1.31]; P = 0.55). The need for rescue noninvasive ventilation was significantly lower in the high-flow group than in the VenturiMask group: at 72 hours, 8% versus 17% (adjusted hazard ratio, 0.39 [95% CI, 0.22-0.71]; P = 0.002) and at 28 days, 12% versus 21% (adjusted hazard ratio, 0.52 [95% CI, 0.32-0.83]; P = 0.007). Conclusions: Reintubation rate did not significantly differ between patients treated with VenturiMask or high-flow oxygen after extubation. High-flow oxygen yielded less frequent use of rescue noninvasive ventilation. Clinical trial registered with www.clinicaltrials.gov (NCT02107183).

How to recognize patients at risk of self-inflicted lung injury

INTRODUCTION

Patient self-inflicted lung injury (P-SILI) has been proposed as a form of lung injury caused by strong inspiratory efforts consequent to a high respiratory drive in patients with hypoxemic acute respiratory failure (hARF). Increased respiratory drive and effort may lead to variable combinations of deleterious phenomena, such as excessive transpulmonary pressure, pendelluft, intra-tidal recruitment, local lung volutrauma, and pulmonary edema. Gas exchange and respiratory mechanics derangements further increase respiratory drive and effort, thus inducing a vicious circle. Forms of partial ventilatory support may further add to the detrimental effects of P-SILI. Since P-SILI may worsen patient outcome, strategies aimed at identifying and preventing P-SILI would be of great importance.

AREAS COVERED

We systematically searched Pubmed since inception until 15 April 2022 to review the patho-physiological mechanisms of P-SILI and the strategies to identify those patients at risk of P-SILI.

EXPERT OPINION

Although the concept of P-SILI has been increasingly supported by experimental and clinical data, no study has insofar demonstrated the efficacy of any strategy to identify it in the clinical setting. Further research is thus needed to ascertain the detrimental effects of spontaneous breathing and identify patients with hARF at high risk of developing P-SILI.

The role of diaphragmatic thickness measurement in weaning prediction and its comparison with rapid shallow breathing index: a single-center experience

Background: Acute respiratory failure (ARF) is commonly managed with invasive mechanical ventilation (IMV). The majority of the time that a patient spends on IMV is in the process of weaning. Prediction of the weaning outcome is of paramount importance, as untimely/delayed extubation is associated with a high risk of mortality. Diaphragmatic ultrasonography is a promising tool in the intensive care unit, and its utility in predicting the success of weaning remains understudied.Methods: In this prospective-observational study, we recruited 54 ARF patients on IMV, along with 50 healthy controls. During a spontaneous breathing trial, all subjects underwent diaphragmatic ultrasonography along with a rapid shallow breathing index (RSBI) assessment.Results: The mean age was 41.8±17.0 and 37.6±10.5 years among the cases and control group, respectively. Demographic variables were broadly similar in the two groups. The most common cause of ARF was obstructive airway disease. The average duration of IMV was 5.41±2.81 days. Out of 54 subjects, 45 were successfully weaned, while nine patients failed weaning. Age, body mass index, and severity of disease were similar in the successful and failed weaning patients. The sensitivity in predicting successful weaning of percent change in diaphragmatic thickness (Δtdi%) >29.71% was high (93.33%), while specificity was 66.67%. The sensitivity and specificity of mean diaphragmatic thickness (tdi) end-expiratory >0.178 cm was 60.00% and 77.78%, respectively. RSBI at 1 minute of <93.75 had an equally high sensitivity (93.33%) but a lower specificity (22.22%). Similar results were also found for RSBI measured at 5 minutes.Conclusions: During the weaning assessment, the purpose is to minimize both premature as well as delayed extubation. We found that diaphragmatic ultrasonography, in particular Δtdi%, is better than RSBI in predicting weaning outcomes.

A Novel Non-invasive Index of Cardiopulmonary Reserve for the Prediction of Failure of Weaning From Mechanical Ventilation

Purpose: To develop an easy-to-implement prediction index of weaning failure for ICU patients.

Materials and methods: We developed a prediction index modifying respiratory exchange ratio (RER), Mod-RER, a parameter measured during the cardiopulmonary exercise test (CPET) based on respiratory quotient. The Mod-RER index is the ratio of partial pressure of CO₂ in central venous blood over the difference of partial pressure of O₂ in arterial and central venous blood (Mod-RER=PcvCO₂/PaO₂-PcvO_2, where PcvCO₂ = partial pressure of CO₂ in central venous blood, PaO₂ = partial pressure of O₂ in arterial blood, and PcvO₂ = partial pressure of O₂ in central venous blood). We prospectively tested its predictive value, compared to other indices of weaning outcome, in an observational study of difficult-to-wean ICU patients.

Results:Mod-RER index increased significantly only in failed trials and receiver operating characteristic (ROC) analysis for prediction of outcome based on Mod-RER index change had an area under the curve (AUC) 0.80 (p<0.001). Mod-RER change exhibited the highest sensitivity (84.6%) and specificity (78.1%) among the tested indices, with the optimal cut-off of 19.3%. Comparison of AUCs did not reach statistical significance (p=0.106).

Conclusions: We conclude that Mod-RER index is an accurate, easy-to-use prediction tool of weaning failure, useful in decision making of timely extubation of ICU patients, especially in the demanding era of the coronavirus disease 2019 (COVID-19) pandemic.

To Wean or Not to Wean: A Practical Patient Focused Guide to Ventilator Weaning

Since the inception of critical care medicine and artificial ventilation, literature and research on weaning has transformed daily patient care in intensive care units (ICU). As our knowledge of mechanical ventilation (MV) improved, so did the need to study patient-ventilator interactions and weaning predictors. Randomized trials have evaluated the use of protocol-based weaning (vs. usual care) to study the duration of MV in ICUs, different techniques to conduct spontaneous breathing trials (SBT), and strategies to eventually extubate a patient whose initial SBT failed. Despite considerable milestones in the management of multiple diseases contributing to reversible respiratory failure, in the application of early rehabilitative interventions to preserve muscle integrity, and in ventilator technology that mitigates against ventilator injury and dyssynchrony, major barriers to successful liberation from MV persist. This review provides a broad encompassing view of weaning classification, causes of weaning failure, and evidence behind weaning predictors and weaning modes.

Mean platelet volume is useful for predicting weaning failure: a retrospective, observational study

Background

To evaluate the usefulness of mean platelet volume (MPV), a marker of inflammation and stress, for predicting weaning failure in patients undergoing invasive mechanical ventilation (IMV) compared to traditional inflammation markers.

Methods

The retrospective observational study including patients who received IMV and underwent spontaneous breathing trial (SBT) was conducted in ICU at Beijing Chao-Yang hospital in China from January, 2013 to December, 2019. According to the weaning outcome, MPV, leukocyte count and C-reaction protein(CRP) were compared between weaning failure and weaning success group. Receiver-operating characteristics (ROC) curves and multivariate logistical regression analysis were constructed to analyze the value of these inflammatory markers for predicting weaning failure.

Results

A total of 261 patients were enrolled in the study and 54 patients (20.7%) experienced weaning failure (45 SBT failure and 9 extubation failure after successful SBT). MPV was a better predictor for weaning failure (AUC 0.777;95%CI, 0.722–0.826) than leukocyte count (AUC 0.6;95%CI,0.538–0.66) and CRP (0.627;95%CI,0.565–0.685). The cutoff value of MPV for predicting weaning failure was 11.3 fl with sensitivity 55.56%, specificity 87.92%, and diagnostic accuracy 81.22%. According to multivariate logistic regression analyses, MPV > 11.3 fl was an independent risk factor for predicting weaning failure.

Conclusions

MPV could be a more valuable marker for predicting weaning failure. and the patients with MPV > 11.3 fl should be attentively evaluated before weaning since they are at high risk of weaning failure, and it would be auspicable for those patients to undergo a noninvasive ventilation or high-flow nasal cannula oxygen therapy after extubation or even an early tracheostomy.

An overview of noninvasive ventilation in cystic fibrosis

Noninvasive ventilation (NIV) use was initially reported in cystic fibrosis (CF) in 1991 as a bridge to lung transplantation, and over the decades, the use of NIV has increased in the CF population. Individuals with CF are prone to various physiologic changes as lung function worsens, and they benefit from NIV for advanced lung disease. As life expectancy in CF has been increasing due to advances such as highly effective modulator therapy, people with CF may also benefit from NIV for other diagnosis beyond advanced lung disease. NIV can improve gas exchange, quality of sleep, exercise tolerance, and augment airway clearance in CF. CF providers can readily become comfortable with this therapeutic modality. In this review, we will summarize the physiologic basis for NIV use in CF, describe indications for initiation, and discuss how to order and monitor patients on NIV. We will discuss aspects unique to people with CF and the use of NIV, as well as suggestions on how to reduce risks such as infection. We hope that this serves as a resource for CF providers, in particular those who do not have dedicated training in sleep medicine as we all continue to care for the CF patient population.

A Simple Weaning Model Based on Interpretable Machine Learning Algorithm for Patients With Sepsis: A Research of MIMIC-IV and eICU Databases

Background

Invasive mechanical ventilation plays an important role in the prognosis of patients with sepsis. However, there are, currently, no tools specifically designed to assess weaning from invasive mechanical ventilation in patients with sepsis. The aim of our study was to develop a practical model to predict weaning in patients with sepsis.

Methods

We extracted patient information from the Medical Information Mart for Intensive Care Database-IV (MIMIC-IV) and the eICU Collaborative Research Database (eICU-CRD). Kaplan–Meier curves were plotted to compare the 28-day mortality between patients who successfully weaned and those who failed to wean. Subsequently, MIMIC-IV was divided into a training set and an internal verification set, and the eICU-CRD was designated as the external verification set. We selected the best model to simplify the internal and external validation sets based on the performance of the model.

Results

A total of 5020 and 7081 sepsis patients with invasive mechanical ventilation in MIMIC-IV and eICU-CRD were included, respectively. After matching, weaning was independently associated with 28-day mortality and length of ICU stay (p &lt; 0.001 and p = 0.002, respectively). After comparison, 35 clinical variables were extracted to build weaning models. XGBoost performed the best discrimination among the models in the internal and external validation sets (AUROC: 0.80 and 0.86, respectively). Finally, a simplified model was developed based on XGBoost, which included only four variables. The simplified model also had good predictive performance (AUROC:0.75 and 0.78 in internal and external validation sets, respectively) and was developed into a web-based tool for further review.

Conclusions

Weaning success is independently related to short-term mortality in patients with sepsis. The simplified model based on the XGBoost algorithm provides good predictive performance and great clinical applicablity for weaning, and a web-based tool was developed for better clinical application.

Mechanical power normalized to lung-thorax compliance indicates weaning readiness in prolonged ventilated patients

Since critical respiratory muscle workload is a significant determinant of weaning failure, applied mechanical power (MP) during artificial ventilation may serve for readiness testing before proceeding on a spontaneous breathing trial (SBT). Secondary analysis of a prospective, observational study in 130 prolonged ventilated, tracheotomized patients. Calculated MP’s predictive SBT outcome performance was determined using the area under receiver operating characteristic curve (AUROC), measures derived from k-fold cross-validation (likelihood ratios, Matthew's correlation coefficient [MCC]), and a multivariable binary logistic regression model. Thirty (23.1%) patients failed the SBT, with absolute MP presenting poor discriminatory ability (MCC 0.26; AUROC 0.68, 95%CI [0.59‒0.75], p = 0.002), considerably improved when normalized to lung-thorax compliance (LTC_dyn-MP, MCC 0.37; AUROC 0.76, 95%CI [0.68‒0.83], p < 0.001) and mechanical ventilation P_aCO₂ (so-called power index of the respiratory system [PI_rs]: MCC 0.42; AUROC 0.81 [0.73‒0.87], p < 0.001). In the logistic regression analysis, PI_rs (OR 1.48 per 1000 cmH₂O²/min, 95%CI [1.24‒1.76], p < 0.001) and its components LTC_dyn-MP (1.25 per 1000 cmH₂O²/min, [1.06‒1.46], p < 0.001) and mechanical ventilation P_aCO₂ (1.17 [1.06‒1.28], p < 0.001) were independently related to SBT failure. MP normalized to respiratory system compliance may help identify prolonged mechanically ventilated patients ready for spontaneous breathing.

Weaning Failure in Critically Ill Patients Is Related to the Persistence of Sepsis Inflammation

Introduction: Septic patients undergoing mechanical ventilation (MV) often experience difficulty in weaning. Th aim of this study was to determine whether inflammatory biomarkers of sepsis could be indicative of the failure or success of spontaneous breathing trial (SBT) in these patients. Methods: Sixty-five patients on MV (42 septic and 23 intubated for other reasons) fulfilling the criteria for SBT were included in the study. Blood samples were collected right before, at the end of (30 min) and 24 h after the SBT. Serum inflammatory mediators associated with sepsis (IL-18, IL-18BP, TNF) were determined and correlated with the outcome of SBT. Results: A successful SBT was achieved in 45 patients (69.2%). Septic patients had a higher percentage of SBT failure as compared to non-septic patients (85% vs. 15%, p = 0.026), with an odds ratio for failing 4.5 times (OR = 4.5 95%CI: 1.16–17.68, p 0.022). IL-18 levels and the relative mRNA expression in serum were significantly higher in septic as compared to non-septic patients (p < 0.05). Sepsis was independently associated with higher serum IL-18 and TNF levels in two time-point GEE models (53–723, p = 0.023 and 0.3–64, p = 0.048, respectively). IL-18BP displayed independent negative association with rapid shallow breathing index (RSBI) (95% CI: −17.6 to −4, p = 0.002). Conclusion: Sustained increased levels of IL-18 and IL-18BP, acknowledged markers of sepsis, were found to be indicative of SBT failure in patients recovering from sepsis. Our results show that, although subclinical, remaining septic inflammation that sustaines for a long time complicates the weaning procedure. Biomarkers for the estimation of the septic burden and the right time for weaning are needed.

Impact of Reverse Triggering Dyssynchrony During Lung-Protective Ventilation on Diaphragm Function: An Experimental Model

RATIONALE

Reverse triggering is a patient-ventilator interaction where a respiratory muscle contraction is triggered by a passive mechanical insufflation. Its impact on diaphragm structure and function is unknown.

OBJECTIVE

To establish an animal model of reverse triggering with lung injury receiving lung-protective ventilation and to assess its impact on structure and function of the diaphragm.

METHODS

Lung injury was induced by surfactant depletion and high stress ventilation in 32 ventilated pigs. Animals were allocated to receive passive mechanical ventilation or a lung-protective strategy with adjustments facilitating the occurrence of reverse triggering for 3 hours. Diaphragm function (transdiaphragmatic pressure (Pdi) during phrenic nerve stimulation [Force/frequency curve]) and structure (biopsies) were assessed. The impact of reverse triggering on diaphragm function was analyzed according to the breathing effort.

RESULTS

Compared to passive ventilation, the protective ventilation group with reverse triggering received significantly lower tidal volume (7 vs 10 ml/kg) and higher respiratory rate (45 vs 31 bpm). An entrainment pattern of 1:1 was frequent. Breathing effort induced by reverse triggering was highly variable across animals. Reverse triggering with the lowest tercile of breathing effort was associated with 23% higher twitch Pdi compared to passive ventilation, whereas reverse triggering with high breathing effort was associated with a 10% lower twitch Pdi and a higher proportion of abnormal muscle fibers.

CONCLUSION

In a reproducible animal model of reverse triggering with variable levels of breathing effort and entrainment patterns, reverse triggering with high effort is associated with impaired diaphragm function whereas reverse triggering with low effort is associated with preserved diaphragm force.

Ultrasonographic assessment of diaphragmatic contraction and relaxation properties: correlations of diaphragmatic displacement with oesophageal and transdiaphragmatic pressure

Transdiaphragmatic (Pdi) and oesophageal pressures (Pes) are useful in understanding the pathophysiology of the respiratory system. They provide insight into respiratory drive, intrinsic positive end-expiratory pressure, diaphragmatic fatigue and weaning failure.

Biosignal-Based Digital Biomarkers for Prediction of Ventilator Weaning Success

We evaluated new features from biosignals comprising diverse physiological response information to predict the outcome of weaning from mechanical ventilation (MV). We enrolled 89 patients who were candidates for weaning from MV in the intensive care unit and collected continuous biosignal data: electrocardiogram (ECG), respiratory impedance, photoplethysmogram (PPG), arterial blood pressure, and ventilator parameters during a spontaneous breathing trial (SBT). We compared the collected biosignal data's variability between patients who successfully discontinued MV (n = 67) and patients who did not (n = 22). To evaluate the usefulness of the identified factors for predicting weaning success, we developed a machine learning model and evaluated its performance by bootstrapping. The following markers were different between the weaning success and failure groups: the ratio of standard deviations between the short-term and long-term heart rate variability in a Poincaré plot, sample entropy of ECG and PPG, α values of ECG, and respiratory impedance in the detrended fluctuation analysis. The area under the receiver operating characteristic curve of the model was 0.81 (95% confidence interval: 0.70-0.92). This combination of the biosignal data-based markers obtained during SBTs provides a promising tool to assist clinicians in determining the optimal extubation time.

The Risk Factors for Weaning Failure of Mechanically Ventilated Patients With COVID-19: A Retrospective Study in National Medical Team Work

Purpose: This study aimed to describe the clinical and laboratory characteristics and the parameters of the respiratory mechanics of mechanically ventilated patients with confirmed COVID-19 pneumonia and to clarify the risk or protective factors for weaning failure. Methods: Patients diagnosed with COVID-19 pneumonia were selected from the special intensive care unit (ICU) of the Sino-French New City Branch of Tong Ji Hospital, Wuhan, and treated by the National Medical Team Work. They were divided into successful weaning (SW) group (N = 15) and unsuccessful weaning (USW) group (N = 18) according to the prognosis. Information of these patients was analyzed. Results: There were 33 patients included in this study. Patients in the USW group were associated with a poor outcome; the 28-day mortality rate was higher than in the SW group (86.7 vs. 16.7% p < 0.001). By comparison, we found that the initial plateau pressure (Pplat) and driving pressure (DP) of the USW group were higher and that compliance was lower than that of the SW group, but there was no difference between positive end-expiratory pressure (PEEP), partial pressure of carbon dioxide (PCO2), and the ratio of partial pressure arterial oxygen and fraction of inspired oxygen (P/F ratio). Comparing the worst respiratory mechanics parameters of the two groups, the results of the Pplat, DP, compliance, and PEEP were the same as the initial data. The PCO2 of the USW group was higher, while the P/F ratio was lower. A logistic regression analysis suggested that higher Pplat might be an independent risk factor and that higher compliance and lower DP might be protective factors for weaning failure of invasive mechanically ventilated patients with COVID-19 pneumonia. Conclusions: Patients with USW were associated with a poor outcome, higher Pplat might be a risk factor, and a higher compliance and a lower DP might be protective factors for the weaning failure of ventilated COVID-19 patients. Mechanical ventilation settings will affect the patient's prognosis.

Does diaphragm ultrasound improve the rapid shallow breathing index accuracy for predicting the success of weaning from mechanical ventilation?

BACKGROUND

This prospective study investigated whether taking into account diaphragmatic excursion (DE) measured by ultrasonography would improve the performance of the rapid shallow breathing index (RSBI) to predict extubation success or failure.

OBJECTIVES

The aim of the study was to compare the new composite index named the rapid shallow diaphragmatic index (RSDI), and the RSBI measured during a spontaneous breathing trial regarding their ability to predict the need for re-intubation at 72 h.

METHODS

One hundred mechanically ventilated patients underwent daily 30-min spontaneous breathing trials (SBTs) under pressure support ventilation of 6 cm H₂O and end-expiratory pressure of 0 cm H₂O until the SBT was considered successful and followed by extubation. The performances of RSBI (respiratory rate/tidal volume) and of the ratio RSBI/DE measured at 5 and 25 min of the successful SBT were compared in terms of area under the receiver operating characteristics curve (AUC), for predicting extubation success at 72 h. As secondary analysis, extubation and weaning success at 7 d were also considered. As exploratory analyses, predictive indices incorporating both clinical characteristics, the DE, and ultrasound diaphragm thickening fraction (DTF) were investigated.

RESULTS

RSBI and RSBI/DE showed AUCs with 95% confidence intervals consistently extending below 0.50, either at the 5th (0.55 [0.36-0.74] and 0.55 [0.34-0.75], respectively) or at the 25th minute of SBT (0.49 [0.27-0.71] and 0.50 [0.29-0.68], respectively) for predicting weaning success at 72 h or at 7 d (5th min: 0.53 [0.37-0.70] and 0.54 [0.37-0.70], respectively; 25th min: 0.54 [0.37-0.71] and 0.55 [0.39-0.71], respectively). An exploratory index incorporating the accessory respiratory muscle activity, DE, DTF, and respiratory rate at 5th min of SBT showed AUCs for predicting extubation success at 7 d in the 78 patients with DTF measurement (0.77 [0.64-0.90]) that were significantly higher than that of the RSBI (P = 0.017) and RSBI/DE (P < 0.001) in the same respective populations.

CONCLUSIONS

The RSBI and the ratio RSBI/DE failed to predict weaning success when measured during an SBT performed under minimal pressure support. Predictive indices incorporating ultrasound DE and DTF may merit further investigation.

Abdominal Muscle Use During Spontaneous Breathing and Cough in Patients Who Are Mechanically Ventilated: A Bi-center Ultrasound Study

BACKGROUND

Ultrasound may be useful to assess the structure, activity, and function of the abdominal muscles in patients who are mechanically ventilated.

RESEARCH QUESTION

Does measurement of abdominal muscle thickening on ultrasound in patients who are mechanically ventilated provide clinically relevant information about abdominal muscle function and weaning outcomes?

STUDY DESIGN AND METHODS

This study consisted of two parts, a physiological study conducted in healthy subjects and a prospective observational study in patients who were mechanically ventilated. Abdominal muscle thickness and thickening fraction were measured during cough and expiratory efforts in 20 healthy subjects and prior to and during a spontaneous breathing trial in 57 patients being ventilated.

RESULTS

In healthy subjects, internal oblique and rectus abdominis thickening fraction correlated with pressure generated during expiratory efforts (P < .001). In patients being ventilated, abdominal muscle thickness and thickening fraction were feasible to measure in all patients, and reproducibility was moderately acceptable. During a failed spontaneous breathing trial, thickening fraction of transversus abdominis and internal oblique increased substantially from baseline (13.2% [95% CI, 0.9-24.8] and 7.2% [95% CI, 2.2-13.2], respectively). The combined thickening fraction of transversus abdominis, internal oblique, and rectus abdominis measured during cough was associated with an increased risk of reintubation or reconnection to the ventilator following attempted liberation (OR, 2.1; 95% CI, 1.1-4.4 per 10% decrease in thickening fraction).

INTERPRETATION

Abdominal muscle thickening on ultrasound was correlated to the airway pressure generated by expiratory efforts. In patients who were mechanically ventilated, abdominal muscle ultrasound measurements are feasible and moderately reproducible. Among patients who passed a spontaneous breathing trial, reduced abdominal muscle thickening during cough was associated with a high risk of liberation failure.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov; No.: NCT03567564; URL: www.clinicaltrials.gov.

Premature, Opportune, and Delayed Weaning in Mechanically Ventilated Patients: A Call for Implementation of Weaning Protocols in Low- and Middle-Income Countries

OBJECTIVES

Weaning protocols establish readiness-to-wean criteria to determine the opportune moment to conduct a spontaneous breathing trial. Weaning protocols have not been widely adopted or evaluated in ICUs in low- and middle-income countries. We sought to compare clinical outcomes between participants whose weaning trials were retrospectively determined to have been premature, opportune, or delayed based on when they met readiness-to-wean criteria.

DESIGN

Prospective, multicenter observational study.

SETTING

Five medical ICUs in four public hospitals in Lima, Perú.

SUBJECTS

Adults with acute respiratory failure and at least 24 hours of invasive mechanical ventilation (n = 1,657).

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

We established six readiness-to-wean criteria and retrospectively categorized our sample into three weaning groups: 1) premature: if the weaning trial took place before fulfilling all criteria, 2) opportune: if the weaning trial took place within 24 hours after fulfilling the criteria, and 3) delayed: if the weaning trial took place over 24 hours after fulfilling criteria. We compared 90-day mortality, ventilator-free days, ICU-free days, and hospital-free days between premature, opportune, and delayed weaning groups. In our sample, 761 participants (60.8%) were classified as having a premature weaning trial, 196 underwent opportune weaning (15.7%), and 295 experienced delayed weaning (23.6%). There was no significant difference in 90-day mortality between the groups. Both the premature and delayed weaning groups had poorer clinical outcomes with fewer ventilator-free days (-2.18, p = 0.008) and (-3.49, p < 0.001), ICU-free days (-2.25, p = 0.001) and (-3.72, p < 0.001), and hospital-free days (-2.76, p = 0.044) and (-4.53, p = 0.004), respectively, compared with the opportune weaning group.

CONCLUSIONS

Better clinical outcomes occur with opportune weaning compared with premature and delayed weaning. If readiness-to-wean criteria can be applied in resource-limited settings, it may improve ICU outcomes associated with opportune weaning.

Role of a successful spontaneous breathing trial in ventilator liberation in brain-injured patients

BACKGROUND

Spontaneous breathing trials (SBTs) have been shown to improve outcomes in critically ill patients. However, in patients with brain injury, indications for intubation and mechanical ventilation are different from those of non-neurological patients, and the role of an SBT in patients with brain injury is less established. The aim of the present study was to compare key respiratory variables acquired during a successful SBT between patients with successful ventilator liberation versus failed ventilator liberation.

METHODS

In this prospective study, patients with brain injury (≥18 years of age), who completed a 30-min SBT, were enrolled. Airway pressure, flow, esophageal pressure, and diaphragm electrical activity (ΔEAdi) were recorded before (baseline) and during the SBT. Respiratory rate (RR), tidal volume, inspiratory muscle pressure (ΔPmus), ΔEAdi, and neuromechanical efficiency (ΔPmus/ΔEAdi) of the diaphragm were calculated breath by breath and compared between the liberation success and failure groups. Failed liberation was defined as the need for invasive ventilator assistance within 48 h after the SBT.

RESULTS

In total, 46 patients (51.9±13.2 years, 67.4% male) completed the SBT. Seventeen (37%) patients failed ventilator liberation within 48 h. Another 11 patients required invasive ventilation within 7 days after completing the SBT. There were no differences in baseline characteristics between the success and failed groups. In-depth analysis showed similar changes in patterns and values of respiratory physiological parameters between the groups.

CONCLUSIONS

In patients with brain injury, ventilator liberation failure was common after successful SBT. In-depth physiological analysis during the SBT did not provide data to predict successful liberation in these patients.

TRIAL REGISTRATION

The trial was registered at ClinicalTrials.gov (No. NCT02863237).

Esophageal Manometry

The estimation of pleural pressure with esophageal manometry has been used for decades, and it has been a fertile area of physiology research in healthy subject as well as during mechanical ventilation in patients with lung injury. However, its scarce adoption in clinical practice takes its roots from the (false) ideas that it requires expertise with years of training, that the values obtained are not reliable due to technical challenges or discrepant methods of calculation, and that measurement of esophageal pressure has not proved to benefit patient outcomes. Despites these criticisms, esophageal manometry could contribute to better monitoring, optimization, and personalization of mechanical ventilation from the acute initial phase to the weaning period. This review aims to provide a comprehensive but comprehensible guide addressing the technical aspects of esophageal catheter use, its application in different clinical situations and conditions, and an update on the state of the art with recent studies on this topic and on remaining questions and ways for improvement.

Prolonged Weaning: S2k Guideline Published by the German Respiratory Society

Mechanical ventilation (MV) is an essential part of modern intensive care medicine. MV is performed in patients with severe respiratory failure caused by respiratory muscle insufficiency and/or lung parenchymal disease; that is, when other treatments such as medication, oxygen administration, secretion management, continuous positive airway pressure (CPAP), or nasal high-flow therapy have failed. MV is required for maintaining gas exchange and allows more time to curatively treat the underlying cause of respiratory failure. In the majority of ventilated patients, liberation or "weaning" from MV is routine, without the occurrence of any major problems. However, approximately 20% of patients require ongoing MV, despite amelioration of the conditions that precipitated the need for it in the first place. Approximately 40-50% of the time spent on MV is required to liberate the patient from the ventilator, a process called "weaning". In addition to acute respiratory failure, numerous factors can influence the duration and success rate of the weaning process; these include age, comorbidities, and conditions and complications acquired during the ICU stay. According to international consensus, "prolonged weaning" is defined as the weaning process in patients who have failed at least 3 weaning attempts, or require more than 7 days of weaning after the first spontaneous breathing trial (SBT). Given that prolonged weaning is a complex process, an interdisciplinary approach is essential for it to be successful. In specialised weaning centres, approximately 50% of patients with initial weaning failure can be liberated from MV after prolonged weaning. However, the heterogeneity of patients undergoing prolonged weaning precludes the direct comparison of individual centres. Patients with persistent weaning failure either die during the weaning process, or are discharged back to their home or to a long-term care facility with ongoing MV. Urged by the growing importance of prolonged weaning, this Sk2 Guideline was first published in 2014 as an initiative of the German Respiratory Society (DGP), in conjunction with other scientific societies involved in prolonged weaning. The emergence of new research, clinical study findings and registry data, as well as the accumulation of experience in daily practice, have made the revision of this guideline necessary. The following topics are dealt with in the present guideline: Definitions, epidemiology, weaning categories, underlying pathophysiology, prevention of prolonged weaning, treatment strategies in prolonged weaning, the weaning unit, discharge from hospital on MV, and recommendations for end-of-life decisions. Special emphasis was placed on the following themes: (1) A new classification of patient sub-groups in prolonged weaning. (2) Important aspects of pulmonary rehabilitation and neurorehabilitation in prolonged weaning. (3) Infrastructure and process organisation in the care of patients in prolonged weaning based on a continuous treatment concept. (4) Changes in therapeutic goals and communication with relatives. Aspects of paediatric weaning are addressed separately within individual chapters. The main aim of the revised guideline was to summarize both current evidence and expert-based knowledge on the topic of "prolonged weaning", and to use this information as a foundation for formulating recommendations related to "prolonged weaning", not only in acute medicine but also in the field of chronic intensive care medicine. The following professionals served as important addressees for this guideline: intensivists, pulmonary medicine specialists, anaesthesiologists, internists, cardiologists, surgeons, neurologists, paediatricians, geriatricians, palliative care clinicians, rehabilitation physicians, intensive/chronic care nurses, physiotherapists, respiratory therapists, speech therapists, medical service of health insurance, and associated ventilator manufacturers.

Techniques to monitor respiratory drive and inspiratory effort

PURPOSE OF REVIEW

There is increased awareness that derangements of respiratory drive and inspiratory effort are frequent and can result in lung and diaphragm injury together with dyspnea and sleep disturbances. This review aims to describe available techniques to monitor drive and effort.

RECENT FINDINGS

Measuring drive and effort is necessary to quantify risk and implement strategies to minimize lung and the diaphragm injury by modifying sedation and ventilation. Evidence on the efficacy of such strategies is yet to be elucidated, but physiological and epidemiological data support the need to avoid injurious patterns of breathing effort.Some techniques have been used in research for decades (e.g., esophageal pressure or airway occlusion pressure), evidence on their practical utility is growing, and technical advances have eased implementation. More novel techniques (e.g., electrical activity of the diaphragm and ultrasound) are being investigated providing new insights on their use and interpretation.

SUMMARY

Available techniques provide reliable measures of the intensity and timing of drive and effort. Simple, noninvasive techniques might be implemented in most patients and the more invasive or time-consuming in more complex patients at higher risk. We encourage clinicians to become familiar with technical details and physiological rationale of each for optimal implementation.

Ultrasound shear wave elastography for assessing diaphragm function in mechanically ventilated patients: a breath-by-breath analysis

Background

Diaphragm dysfunction is highly prevalent in mechanically ventilated patients. Recent work showed that changes in diaphragm shear modulus (ΔSMdi) assessed using ultrasound shear wave elastography (SWE) are strongly related to changes in Pdi (ΔPdi) in healthy subjects. The aims of this study were to investigate the relationship between ΔSMdi and ΔPdi in mechanically ventilated patients, and whether ΔSMdi is responsive to change in respiratory load when varying the ventilator settings.

Methods

A prospective, monocentric study was conducted in a 15-bed ICU. Patients were included if they met the readiness-to-wean criteria. Pdi was continuously monitored using a double-balloon feeding catheter orally introduced. The zone of apposition of the right hemidiaphragm was imaged using a linear transducer (SL10-2, Aixplorer, Supersonic Imagine, France). Ultrasound recordings were performed under various pressure support settings and during a spontaneous breathing trial (SBT). A breath-by-breath analysis was performed, allowing the direct comparison between ΔPdi and ΔSMdi. Pearson’s correlation coefficients (r) were used to investigate within-individual relationships between variables, and repeated measure correlations (R) were used for determining overall relationships between variables. Linear mixed models were used to compare breathing indices across the conditions of ventilation.

Results

Thirty patients were included and 930 respiratory cycles were analyzed. Twenty-five were considered for the analysis. A significant correlation was found between ΔPdi and ΔSMdi (R = 0.45, 95% CIs [0.35 0.54], p < 0.001). Individual correlation displays a significant correlation in 8 patients out of 25 (r = 0.55–0.86, all p < 0.05, versus r = − 0.43–0.52, all p > 0.06). Changing the condition of ventilation similarly affected ΔPdi and ΔSMdi. Patients in which ΔPdi–ΔSMdi correlation was non-significant had a faster respiratory rate as compared to that of patient with a significant ΔPdi–ΔSMdi relationship (median (Q1–Q3), 25 (18–33) vs. 21 (15–26) breaths.min⁻¹, respectively).

Conclusions

We demonstrate that ultrasound SWE may be a promising surrogate to Pdi in mechanically ventilated patients. Respiratory rate appears to negatively impact SMdi measurement. Technological developments are needed to generalize this method in tachypneic patients.

Trial registration

NCT03832231.

Lung- and Diaphragm-Protective Ventilation

Mechanical ventilation can cause acute diaphragm atrophy and injury, and this is associated with poor clinical outcomes. Although the importance and impact of lung-protective ventilation is widely appreciated and well established, the concept of diaphragm-protective ventilation has recently emerged as a potential complementary therapeutic strategy. This Perspective, developed from discussions at a meeting of international experts convened by PLUG (the Pleural Pressure Working Group) of the European Society of Intensive Care Medicine, outlines a conceptual framework for an integrated lung- and diaphragm-protective approach to mechanical ventilation on the basis of growing evidence about mechanisms of injury. We propose targets for diaphragm protection based on respiratory effort and patient-ventilator synchrony. The potential for conflict between diaphragm protection and lung protection under certain conditions is discussed; we emphasize that when conflicts arise, lung protection must be prioritized over diaphragm protection. Monitoring respiratory effort is essential to concomitantly protect both the diaphragm and the lung during mechanical ventilation. To implement lung- and diaphragm-protective ventilation, new approaches to monitoring, to setting the ventilator, and to titrating sedation will be required. Adjunctive interventions, including extracorporeal life support techniques, phrenic nerve stimulation, and clinical decision-support systems, may also play an important role in selected patients in the future. Evaluating the clinical impact of this new paradigm will be challenging, owing to the complexity of the intervention. The concept of lung- and diaphragm-protective ventilation presents a new opportunity to potentially improve clinical outcomes for critically ill patients.

Esophageal and transdiaphragmatic pressure swings as indices of inspiratory effort

AIM

To describe the correlation between the inspiratory esophageal and transdiaphragmatic pressure swings (ΔPes and ΔPdi), easily measured indices of inspiratory effort, with the gold-standard, the transdiaphragmatic pressure time product (PTP_Pdi/min), and assess the accuracy of swing pressures in predicting very high or low effort.

METHOD

Retrospective analysis of data from patients enrolled in four previous studies. ROC curves of ΔPes and ΔPdi values for specific PTP_Pdi/min thresholds (50, 150, 200 cmH₂O × sec/min) were constructed, and the diagnostic accuracy of different thresholds of swing values were computed.

RESULTS

A threshold of inspiratory ΔP<7cmH₂O can be used to identify most patients with low effort, as lower ΔP thresholds have low sensitivity. Thresholds of inspiratory ΔP>14-18cmH₂O can be used to identify patients with very high inspiratory effort (PTP_Pdi/min> 200 cmH₂O × sec/min).

CONCLUSIONS

The results of this study can help clinicians better select and interpret thresholds of ΔP to evaluate inspiratory effort.

Kinetics of oxygen uptake during unassisted breathing trials in prolonged mechanical ventilation: a prospective pilot study

Few studies have investigated the measurement of oxygen uptake (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\dot{\text{V}}}$$\end{document}V˙O₂) in tracheostomized patients undergoing unassisted breathing trials (UBTs) for liberation from mechanical ventilation (MV). Using an open-circuit, breath-to-breath method, we continuously measured \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\dot{\text{V}}}$$\end{document}V˙O₂ and relevant parameters during 120-min UBTs via a T-tube in 49 tracheostomized patients with prolonged MV, and calculated mean values in the first and last 5-min periods. Forty-one (84%) patients successfully completed the UBTs. The median \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\dot{\text{V}}}$$\end{document}V˙O₂ increased significantly (from 235.8 to 298.2 ml/min; P = 0.025) in the failure group, but there was no significant change in the success group (from 223.1 to 221.6 ml/min; P = 0.505). In multivariate logistic regression analysis, an increase in \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\dot{\text{V}}}$$\end{document}V˙O₂ > 17% from the beginning period (odds ratio [OR] 0.084; 95% confidence interval [CI] 0.012–0.600; P = 0.014) and a peak inspiratory pressure greater than − 30 cmH₂O (OR 11.083; 95% CI 1.117–109.944; P = 0.04) were significantly associated with the success of 120-min UBT. A refined prediction model combining heart rate, energy expenditure, end-tidal CO₂ and oxygen equivalent showed a modest increase in the area under the receiver operating characteristic curve of 0.788 (P = 0.578) and lower Akaike information criterion score of 41.83 compared to the traditional prediction model including heart rate and respiratory rate for achieving 48 h of unassisted breathing. Our findings show the potential of monitoring \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\dot{\text{V}}}$$\end{document}V˙O₂ in the final phase of weaning in tracheostomized patients with prolonged MV.

The Impact of Mechanical Ventilation Duration on the Readmission to Intensive Care Unit: A Population-Based Observational Study

Background

If the duration of mechanical ventilation (MV) is related with the intensive care unit (ICU) readmission must be clarified. The purpose of this study was to elucidate if prolonged MV duration increases ICU readmission rate.

Methods

The present observational cohort study analyzed national healthcare claims data from 2006 to 2015. Critically ill patients who received MV in the ICU were classified into five groups according to the MV duration: MV for <7 days, 7–13 days, 14–20 days, 21–27 days, and ≥28 days. The rate and risk of the ICU readmission were estimated according to the MV duration using the unadjusted and adjusted analyses.

Results

We found that 12,929 patients had at least one episode of MV in the ICU. There was a significant linear relationship between the MV duration and the ICU readmission (R²=0.85, p=0.025). The total readmission rate was significantly higher as the MV duration is prolonged (MV for <7 days, 13.9%; for 7–13 days, 16.7%; for 14–20 days, 19.4%; for 21–27 days, 20.4%; for ≥28 days, 35.7%; p<0.001). The analyses adjusted by covariables and weighted with the multinomial propensity scores showed similar results. In the adjusted regression analysis with a Cox proportional hazards model, the MV duration was significantly related to the ICU readmission (hazard ratio, 1.058 [95% confidence interval, 1.047–1.069], p<0.001).

Conclusion

The rate of readmission to the ICU was significantly higher in patients who received longer durations of the MV in the ICU. In the clinical setting, closer observation of patients discharged from the ICU after prolonged periods of MV is required.

Airway Occlusion Pressure As an Estimate of Respiratory Drive and Inspiratory Effort during Assisted Ventilation

Rationale: Monitoring and controlling respiratory drive and effort may help to minimize lung and diaphragm injury. Airway occlusion pressure (P0.1) is a noninvasive measure of respiratory drive.Objectives: To determine 1) the validity of "ventilator" P0.1 (P0.1vent) displayed on the screen as a measure of drive, 2) the ability of P0.1 to detect potentially injurious levels of effort, and 3) how P0.1vent displayed by different ventilators compares to a "reference" P0.1 (P0.1ref) measured from airway pressure recording during an occlusion.Methods: Analysis of three studies in patients, one in healthy subjects, under assisted ventilation, and a bench study with six ventilators. P0.1vent was validated against measures of drive (electrical activity of the diaphragm and muscular pressure over time) and P0.1ref. Performance of P0.1ref and P0.1vent to detect predefined potentially injurious effort was tested using derivation and validation datasets using esophageal pressure-time product as the reference standard.Measurements and Main Results: P0.1vent correlated well with measures of drive and with the esophageal pressure-time product (within-subjects R² = 0.8). P0.1ref >3.5 cm H₂O was 80% sensitive and 77% specific for detecting high effort (≥200 cm H₂O ⋅ s ⋅ min^-1); P0.1ref ≤1.0 cm H₂O was 100% sensitive and 92% specific for low effort (≤50 cm H₂O ⋅ s ⋅ min^-1). The area under the receiver operating characteristics curve for P0.1vent to detect potentially high and low effort were 0.81 and 0.92, respectively. Bench experiments showed a low mean bias for P0.1vent compared with P0.1ref for most ventilators but precision varied; in patients, precision was lower. Ventilators estimating P0.1vent without occlusions could underestimate P0.1ref.Conclusions: P0.1 is a reliable bedside tool to assess respiratory drive and detect potentially injurious inspiratory effort.

Inhibition of central activation of the diaphragm: a mechanism of weaning failure

During a T-tube trial following disconnection of mechanical ventilation, patients failing the trial do not develop contractile diaphragmatic fatigue despite increases in inspiratory pressure output. Studies in volunteers, patients, and animals raise the possibility of spinal and supraspinal reflex mechanisms that inhibit central-neural output under loaded conditions. We hypothesized that diaphragmatic recruitment is submaximal at the end of a failed weaning trial despite concurrent respiratory distress. Tidal transdiaphragmatic pressure (ΔP_di) and electrical activity (ΔEA_di) were recorded with esophago-gastric catheters during a T-tube trial in 20 critically ill patients. During the T-tube trial, ∆EA_di was greater in weaning failure patients than in weaning success patients (P = 0.049). Despite increases in ΔP_di, from 18.1 ± 2.5 to 25.9 ± 3.7 cm H₂O (P < 0.001), rate of transdiaphragmatic pressure development (from 22.6 ± 3.1 to 37.8 ± 6.7 cm H₂O/s; P < 0.0004), and concurrent respiratory distress, ∆EA_di at the end of a failed T-tube trial was half of maximum, signifying inhibition of central neural output to the diaphragm. The increase in ΔP_di in the weaning failure group, while ∆EA_di remained constant, indicates unexpected improvement in diaphragmatic neuromuscular coupling (from 46.7 ± 6.5 to 57.8 ± 8.4 cm H₂O/%; P = 0.006). Redistribution of neural output to the respiratory muscles characterized by a progressive increase in rib cage and accessory muscle contribution to tidal breathing and expiratory muscle recruitment contributed to enhanced coupling. In conclusion, diaphragmatic recruitment is submaximal at the end of a failed weaning trial despite concurrent respiratory distress. This finding signifies that reflex inhibition of central neural output to the diaphragm contributes to weaning failure.

NEW & NOTEWORTHY Research into pathophysiology of failure to wean from mechanical ventilation has excluded several factors, including contractile fatigue, but the precise mechanism remains unknown. We recorded transdiaphragmatic pressure and diaphragmatic electrical activity in patients undergoing a T-tube trial. Diaphragmatic recruitment was submaximal at the end of a failed trial despite concurrent respiratory distress, signifying that inhibition of central neural output to the diaphragm is an important mechanism of weaning failure.

Oesophageal pressure and respiratory muscle ultrasonographic measurements indicate inspiratory effort during pressure support ventilation

BACKGROUND

Bedside measures of patient effort are essential to properly titrate the level of pressure support ventilation. We investigated whether the tidal swing in oesophageal (ΔPes) and transdiaphragmatic pressure (ΔPdi), and ultrasonographic changes in diaphragm (TFdi) and parasternal intercostal (TFic) thickening are reliable estimates of respiratory effort. The effect of diaphragm dysfunction was also considered.

METHODS

Twenty-one critically ill patients were enrolled: age 73 (14) yr, BMI 27 (7) kg m^-2, and Pao₂/Fio₂ 33.3 (9.2) kPa. A three-level pressure support trial was performed: baseline, 25% (PS-medium), and 50% reduction (PS-low). We recorded the oesophageal and transdiaphragmatic pressure-time products (PTPs), work of breathing (WOB), and diaphragm and intercostal ultrasonography. Diaphragm dysfunction was defined by the Gilbert index.

RESULTS

Pressure support was 9.0 (1.6) cm H₂O at baseline, 6.7 (1.3) (PS-medium), and 4.4 (1.0) (PS-low). ΔPes was significantly associated with the oesophageal PTP (R²=0.868; P<0.001) and the WOB (R²=0.683; P<0.001). ΔPdi was significantly associated with the transdiaphragmatic PTP (R²=0.820; P<0.001). TFdi was only weakly correlated with the oesophageal PTP (R²=0.326; P<0.001), and the correlation improved after excluding patients with diaphragm dysfunction (R²=0.887; P<0.001). TFdi was higher and TFic lower in patients without diaphragm dysfunction: 33.6 (18.2)% vs 13.2 (9.2)% and 2.1 (1.7)% vs 12.7 (9.1)%; P<0.0001.

CONCLUSIONS

ΔPes and ΔPdi are adequate estimates of inspiratory effort. Diaphragm ultrasonography is a reliable indicator of inspiratory effort in the absence of diaphragm dysfunction. Additional measurement of parasternal intercostal thickening may discriminate a low inspiratory effort or a high effort in the presence of a dysfunctional diaphragm.

Long-Term Outcome after Prolonged Mechanical Ventilation. A Long-Term Acute-Care Hospital Study

Rationale: Patients managed at a long-term acute-care hospital (LTACH) for weaning from prolonged mechanical ventilation are at risk for profound muscle weakness and disability. Objectives: To investigate effects of prolonged ventilation on survival, muscle function, and its impact on quality of life at 6 and 12 months after LTACH discharge. Methods: This was a prospective, longitudinal study conducted in 315 patients being weaned from prolonged ventilation at an LTACH. Measurements and Main Results: At discharge, 53.7% of patients were detached from the ventilator and 1-year survival was 66.9%. On enrollment, maximum inspiratory pressure (Pi_max) was 41.3 (95% confidence interval, 39.4-43.2) cm H₂O (53.1% predicted), whereas handgrip strength was 16.4 (95% confidence interval, 14.4-18.7) kPa (21.5% predicted). At discharge, Pi_max did not change, whereas handgrip strength increased by 34.8% (P < 0.001). Between discharge and 6 months, handgrip strength increased 6.2 times more than did Pi_max. Between discharge and 6 months, Katz activities-of-daily-living summary score improved by 64.4%; improvement in Katz summary score was related to improvement in handgrip strength (r = -0.51; P < 0.001). By 12 months, physical summary score and mental summary score of 36-item Short-Form Survey returned to preillness values. When asked, 84.7% of survivors indicated willingness to undergo mechanical ventilation again. Conclusions: Among patients receiving prolonged mechanical ventilation at an LTACH, 53.7% were detached from the ventilator at discharge and 1-year survival was 66.9%. Respiratory strength was well maintained, whereas peripheral strength was severely impaired throughout hospitalization. Six months after discharge, improvement in muscle function enabled patients to perform daily activities, and 84.7% indicated willingness to undergo mechanical ventilation again.

A novel non-invasive method to detect excessively high respiratory effort and dynamic transpulmonary driving pressure during mechanical ventilation

Background

Excessive respiratory muscle effort during mechanical ventilation may cause patient self-inflicted lung injury and load-induced diaphragm myotrauma, but there are no non-invasive methods to reliably detect elevated transpulmonary driving pressure and elevated respiratory muscle effort during assisted ventilation. We hypothesized that the swing in airway pressure generated by respiratory muscle effort under assisted ventilation when the airway is briefly occluded (ΔP_occ) could be used as a highly feasible non-invasive technique to screen for these conditions.

Methods

Respiratory muscle pressure (P_mus), dynamic transpulmonary driving pressure (ΔP_L,dyn, the difference between peak and end-expiratory transpulmonary pressure), and ΔP_occ were measured daily in mechanically ventilated patients in two ICUs in Toronto, Canada. A conversion factor to predict ΔP_L,dyn and P_mus from ΔP_occ was derived and validated using cross-validation. External validity was assessed in an independent cohort (Nanjing, China).

Results

Fifty-two daily recordings were collected in 16 patients. In this sample, P_mus and ΔP_L were frequently excessively high: P_mus exceeded 10 cm H₂O on 84% of study days and ΔP_L,dyn exceeded 15 cm H₂O on 53% of study days. ΔP_occ measurements accurately detected P_mus > 10 cm H₂O (AUROC 0.92, 95% CI 0.83–0.97) and ΔP_L,dyn > 15 cm H₂O (AUROC 0.93, 95% CI 0.86–0.99). In the external validation cohort (n = 12), estimating P_mus and ΔP_L,dyn from ΔP_occ measurements detected excessively high P_mus and ΔP_L,dyn with similar accuracy (AUROC ≥ 0.94).

Conclusions

Measuring ΔP_occ enables accurate non-invasive detection of elevated respiratory muscle pressure and transpulmonary driving pressure. Excessive respiratory effort and transpulmonary driving pressure may be frequent in spontaneously breathing ventilated patients.

Ventilatory equivalent for oxygen as an extubation outcome predictor: A pilot study

Introduction

Weaning predictors can help liberate patients in a timely manner from mechanical ventilation. Ventilatory equivalent for oxygen (VEqO₂), a surrogate for work of breathing and a measure of the efficiency of breathing, may be an important noninvasive alternative to other weaning predictors. Our study’s purpose was to observe any differences in VEqO₂ between extubation outcome groups.

Methods

Employing a metabolic cart, oxygen consumption (V^˙O₂), minute volume (VE), tidal volume (VT), and breathing frequency were recorded during a spontaneous breathing trial (SBT) to calculate VEqO₂ and the rapid shallow breathing index (RSBI) in 34 adult participants in the intensive care unit. Five-breath means of VEqO₂ and the RSBI collected throughout the SBT were examined between SBT pass and fail groups and extubation pass and fail groups using the Mann–Whitney U test with p < 0.05.

Results

Data from 31 participants were analyzed between SBT outcome groups. Data from 20 participants were examined for extubation outcome after a successful SBT. Median (interquartile range) VEqO₂ was not different between extubation groups. Participants who passed the SBT had a higher median VEqO₂ than those who did not at the midpoint (25.3 L/L V^˙O₂ [22–33 L/L V^˙O₂] vs. 23.7 L/L V^˙O₂ [18–24 L/L V^˙O₂], p = 0.035) and at the end (25.5 L/L V^˙O₂ [23–34 L/L V^˙O₂] vs. 21.3 L/L V^˙O₂ [20–24 L/L V^˙O₂], p = 0.017) of the SBT.

Discussion

VEqO₂ may show differences in SBT outcomes, but not differences between extubation outcomes. VEqO₂ may be able to detect differences in work during an SBT, but may not be able to predict change in workload in the respiratory system after extubation. The small sample size may also have prevented any differences in extubation outcomes to be shown.

Conclusion

VEqO₂ was higher in patients that passed their SBT. VEqO₂ was not useful in identifying extubation success or failure in adult mechanically ventilated patients.

ERS statement on respiratory muscle testing at rest and during exercise

Assessing respiratory mechanics and muscle function is critical for both clinical practice and research purposes. Several methodological developments over the past two decades have enhanced our understanding of respiratory muscle function and responses to interventions across the spectrum of health and disease. They are especially useful in diagnosing, phenotyping and assessing treatment efficacy in patients with respiratory symptoms and neuromuscular diseases. Considerable research has been undertaken over the past 17 years, since the publication of the previous American Thoracic Society (ATS)/European Respiratory Society (ERS) statement on respiratory muscle testing in 2002. Key advances have been made in the field of mechanics of breathing, respiratory muscle neurophysiology (electromyography, electroencephalography and transcranial magnetic stimulation) and on respiratory muscle imaging (ultrasound, optoelectronic plethysmography and structured light plethysmography). Accordingly, this ERS task force reviewed the field of respiratory muscle testing in health and disease, with particular reference to data obtained since the previous ATS/ERS statement. It summarises the most recent scientific and methodological developments regarding respiratory mechanics and respiratory muscle assessment by addressing the validity, precision, reproducibility, prognostic value and responsiveness to interventions of various methods. A particular emphasis is placed on assessment during exercise, which is a useful condition to stress the respiratory system.