Coexistence and Impact of Limb Muscle and Diaphragm Weakness at Time of Liberation from Mechanical Ventilation in Medical Intensive Care Unit Patients

Intensive care unit-acquired weakness: unanswered questions and targets for future research

Intensive care unit-acquired weakness (ICU-AW) is the most common neuromuscular impairment in critically ill patients. We discuss critical aspects of ICU-AW that have not been completely defined or that are still under discussion. Critical illness polyneuropathy, myopathy, and muscle atrophy contribute in various proportions to ICU-AW. Diagnosis of ICU-AW is clinical and is based on Medical Research Council sum score and handgrip dynamometry for limb weakness and recognition of a patient's ventilator dependency or difficult weaning from artificial ventilation for diaphragmatic weakness (DW). ICU-AW can be caused by a critical illness polyneuropathy, a critical illness myopathy, or muscle disuse atrophy, alone or in combination. Its diagnosis requires both clinical assessment of muscle strength and complete electrophysiological evaluation of peripheral nerves and muscles. The peroneal nerve test (PENT) is a quick simplified electrophysiological test with high sensitivity and good specificity that can be used instead of complete electrophysiological evaluation as a screening test in non-cooperative patients. DW, assessed by bilateral phrenic nerve magnetic stimulation or diaphragm ultrasound, can be an isolated event without concurrent limb muscle involvement. Therefore, it remains uncertain whether DW and limb weakness are different manifestations of the same syndrome or are two distinct entities. Delirium is often associated with ICU-AW but a clear correlation between these two entities requires further studies. Artificial nutrition may have an impact on ICU-AW, but no study has assessed the impact of nutrition on ICU-AW as the primary outcome. Early mobilization improves activity limitation at hospital discharge if it is started early in the ICU, but beneficial long-term effects are not established. Determinants of ICU-AW can be many and can interact with each other. Therefore, future studies assessing early mobilization should consider a holistic patient approach with consideration of all components that may lead to muscle weakness.

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.

Inability of Diaphragm Ultrasound to Predict Extubation Failure: A Multicenter Study

BACKGROUND

Diaphragmatic dysfunction may promote weaning difficulties in patients who are mechanically ventilated.

OBJECTIVE

The goal of this study was to assess whether diaphragm dysfunction detected by ultrasound prior to extubation could predict extubation failure in the ICU.

METHODS

This multicenter prospective study included patients at high risk of reintubation: those aged > 65 years, with underlying cardiac or respiratory disease, or intubated > 7 days. All patients had successfully undergone a spontaneous breathing trial. Diaphragmatic function was assessed by ultrasound prior to extubation while breathing spontaneously on a T-piece. Bilateral diaphragmatic excursion and apposition thickening fraction were measured, and diaphragmatic dysfunction was defined as excursion < 10 mm or thickening < 30%. Cough strength was clinically assessed by physiotherapists. Extubation failure was defined as reintubation or death within the 7 days following extubation.

RESULTS

Over a 20-month period, 191 at-risk patients were studied. Among them, 33 (17%) were considered extubation failures. The proportion of patients with diaphragmatic dysfunction was similar between those whose extubation succeeded and those whose extubation failed: 46% vs 51% using excursion (P = .55), and 71% vs 68% using thickening (P = .73), respectively. Values of excursion and thickening did not differ between the success and the failure groups: at right, excursion was 14 ± 7 mm vs 11 ± 8 (P = .13), and thickening was 29 ± 29% vs 38 ± 48% (P = .83), respectively. Extubation failure rates were 7%, 22%, and 46% in patients with effective, moderate, and ineffective cough (P < .01). Ineffective cough was the only variable independently associated with extubation failure.

CONCLUSIONS

Diaphragmatic dysfunction assessed by ultrasound was not associated with an increased risk of extubation failure.

Disorders of the Diaphragm

Pathologic processes that involve the central nervous system, phrenic nerve, neuromuscular junction, and skeletal muscle can impair diaphragm function. When these processes are of sufficient severity to cause diaphragm dysfunction, respiratory failure may be a consequence. This article reviews basic diaphragm anatomy and physiology and then discusses diagnostic and therapeutic approaches to disorders that result in unilateral or bilateral diaphragm dysfunction. This discussion provides a context in which disorders of the diaphragm and their implications on respiratory function can be better appreciated.

Assessing Diaphragm Function in Chest Wall and Neuromuscular Diseases

Diaphragm dysfunction is defined as the partial or complete loss of diaphragm muscle contractility. However, because the diaphragm is one of only a few skeletal muscles that is not amenable to direct examination, the tools available for the clinician to assess diaphragm function have been limited. Traditionally, measures of lung volume, inspiratory muscle strength, and radiographic techniques such as fluoroscopy have provided the major method to assess diaphragm function. Measurement of transdiaphragmatic pressure provides the most direct means of evaluating the diaphragm, but this technique is not readily available to clinicians. Diaprhragm ultrasonography is new method that allows for direct examination of the diaphragm.

European Respiratory Society International Congress 2018: highlights from Assembly 2 on respiratory intensive care

The respiratory intensive care Assembly of the European Respiratory Society is proud to present a summary of several important sessions held at the International Congress in Paris in 2018. For the highly esteemed reader who may have missed the Congress, a concise review was written on three topics: the state-of-the-art session on respiratory critical care, hot topics in weaning and the best abstracts in noninvasive ventilation.

The respiratory intensive care Assembly of the European Respiratory Society is proud to present a summary of several important sessions from the 2018 #ERSCongress in Parishttp://ow.ly/6Du830nFESK

A narrative review of diaphragm ultrasound to predict weaning from mechanical ventilation: where are we and where are we heading?

Background

The use of ultrasound to visualize the diaphragm is well established. Over the last 15 years, certain indices of diaphragm function, namely diaphragm thickness, thickening fraction and excursion have been established for mechanically ventilated patients to track changes in diaphragm size and function over time, to assess and diagnose diaphragmatic dysfunction, and to evaluate if these indices can predict successful liberation from mechanical ventilation. In the last 2 years, three meta-analyses and a systematic review have assessed the usability of diaphragmatic ultrasound to predict successful weaning. Since then, further data have been published on the topic.

Conclusions

The aim of this narrative review is to briefly describe the common methods of diaphragmatic function assessment using ultrasound techniques, before summarizing the major points raised by the recent reviews. A narrative summary of the most recent data will be presented, before concluding with a brief discussion of future research directions in this field.

Which ICU patients benefit most from inspiratory muscle training? Retrospective analysis of a randomized trial

Background: Inspiratory muscle training (IMT) increases inspiratory muscle strength and improves quality of life in intensive care unit (ICU) patients who have been invasively mechanically ventilated for ≥7 days. The purpose of this study was to identify which patients benefit most from IMT following weaning from mechanical ventilation. Methods: Secondary analysis of a randomized trial of supervised daily IMT in 70 patients (mean age 59 years) in a 31-bed ICU was carried out. Changes in inspiratory muscle strength (maximum inspiratory pressure, MIP) between enrolment and 2 weeks (ΔMIP) were analyzed to compare the IMT group (71% male) and the control group (58% male). Linear regression models explored which factors at baseline were associated with ΔMIP. Results: Thirty-four participants were allocated to the IMT group where baseline MIP was associated with an increase in ΔMIP, significantly different from the control group (p = 0.025). The highest ΔMIP was associated with baseline MIP ≥ 28 cmH₂O. In the IMT group, higher baseline quality of life (EQ5D) scores were associated with positive ΔMIP, significantly different from the control group (p = 0.029), with largest ΔMIP for those with EQ5D ≥ 40. Conclusions: Physiotherapists should target ICU patients with moderate inspiratory muscle weakness (MIP ≥28 cmH₂O) and moderate to high quality of life (EQ5D>40) within 48 h of ventilatory weaning as ideal candidates for IMT following prolonged mechanical ventilation.

Temporary transvenous diaphragm pacing vs. standard of care for weaning from mechanical ventilation: study protocol for a randomized trial

BACKGROUND

Mechanical ventilation (MV) is a life-saving technology that restores or assists breathing. Like any treatment, MV has side effects. In some patients it can cause diaphragmatic atrophy, injury, and dysfunction (ventilator-induced diaphragmatic dysfunction, VIDD). Accumulating evidence suggests that VIDD makes weaning from MV difficult, which involves increased morbidity and mortality.

METHODS AND ANALYSIS

This paper describes the protocol of a randomized, controlled, open-label, multicenter trial that is designed to investigate the safety and effectiveness of a novel therapy, temporary transvenous diaphragm pacing (TTVDP), to improve weaning from MV in up to 88 mechanically ventilated adult patients who have failed at least two spontaneous breathing trials over at least 7 days. Patients will be randomized (1:1) to TTVDP (treatment) or standard of care (control) groups. The primary efficacy endpoint is time to successful extubation with no reintubation within 48 h. Secondary endpoints include maximal inspiratory pressure and ultrasound-measured changes in diaphragm thickness and diaphragm thickening fraction over time. In addition, observational data will be collected and analyzed, including 30-day mortality and time to discharge from the intensive care unit and from the hospital. The hypothesis to be tested postulates that more TTVDP patients than control patients will be successfully weaned from MV within the 30 days following randomization.

DISCUSSION

This study is the first large-scale clinical trial of a novel technology (TTVDP) aimed at accelerating difficult weaning from MV. The technology tested provides the first therapy directed specifically at VIDD, an important cause of delayed weaning from MV. Its results will help delineate the place of this therapeutic approach in clinical practice and help design future studies aimed at defining the indications and benefits of TTVDP.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT03096639 . Registered on 30 March 2017.

Neurally adjusted ventilatory assist (NAVA) versus pressure support ventilation: patient-ventilator interaction during invasive ventilation delivered by tracheostomy

BACKGROUND

Prolonged weaning is a major issue in intensive care patients and tracheostomy is one of the last resort options. Optimized patient-ventilator interaction is essential to weaning. The purpose of this study was to compare patient-ventilator synchrony between pressure support ventilation (PSV) and neurally adjusted ventilatory assist (NAVA) in a selected population of tracheostomised patients.

METHODS

We performed a prospective, sequential, non-randomized and single-centre study. Two recording periods of 60 min of airway pressure, flow, and electrical activity of the diaphragm during PSV and NAVA were recorded in a random assignment and eight periods of 1 min were analysed for each mode. We searched for macro-asynchronies (ineffective, double, and auto-triggering) and micro-asynchronies (inspiratory trigger delay, premature, and late cycling). The number and type of asynchrony events per minute and asynchrony index (AI) were determined. The two respiratory phases were compared using the non-parametric Wilcoxon test after testing the equality of the two variances (F-Test).

RESULTS

Among the 61 patients analysed, the total AI was lower in NAVA than in PSV mode: 2.1% vs 14% (p < 0.0001). This was mainly due to a decrease in the micro-asynchronies index: 0.35% vs 9.8% (p < 0.0001). The occurrence of macro-asynchronies was similar in both ventilator modes except for double triggering, which increased in NAVA. The tidal volume (ml/kg) was lower in NAVA than in PSV (5.8 vs 6.2, p < 0.001), and the respiratory rate was higher in NAVA than in PSV (28 vs 26, p < 0.05).

CONCLUSION

NAVA appears to be a promising ventilator mode in tracheotomised patients, especially for those requiring prolonged weaning due to the decrease in asynchronies.

[Advances in respiratory assessment and treatment in children undergoing invasive mechanical ventilation]

The widespread use of mechanical ventilation technology has contributed to the successful treatment of many children with respiratory failure. At the same time, forced ventilation and changes in normal respiratory physiology and mechanics may lead to respiratory dysfunction and decreased airway clearance ability. Therefore, how to perform a comprehensive and accurate respiratory function assessment, conduct appropriate respiratory function rehabilitation, perform extubation as soon as possible, and shorten the duration of mechanical ventilation based on the children's own physiological characteristics, is a focus of the research on effective weaning from mechanical ventilation in children with severe conditions. This article reviews the advances in the respiratory function assessment and treatment methods in children undergoing invasive mechanical ventilation.

Proportional modes versus pressure support ventilation: a systematic review and meta-analysis

Background

Proportional modes (proportional assist ventilation, PAV, and neurally adjusted ventilatory assist, NAVA) could improve patient–ventilator interaction and consequently may be efficient as a weaning mode. The purpose of this systematic review is to examine whether proportional modes improved patient–ventilator interaction and whether they had an impact on the weaning success and length of mechanical ventilation, in comparison with PSV.

Methods

We searched PubMed, EMBASE, and the Cochrane Central Register of Controlled Trials from inception through May 13, 2018. We included both parallel-group and crossover randomized studies that examined the efficacy of proportional modes in comparison with PSV in mechanically ventilated adults. The primary outcomes were (1) asynchrony index (AI), (2) weaning failure, and (3) duration of mechanical ventilation.

Results

We included 15 studies (four evaluated PAV, ten evaluated NAVA, and one evaluated both modes). Although the use of proportional modes was not associated with a reduction in AI (WMD − 1.43; 95% CI − 3.11 to 0.25; p = 0.096; PAV—one study, and NAVA—seven studies), the use of proportional modes was associated with a reduction in patients with AI > 10% (RR 0.15; 95% CI 0.04–0.58; p = 0.006; PAV—two studies, and NAVA—five studies), compared with PSV. There was a significant heterogeneity among studies for AI, especially with NAVA. Compared with PSV, use of proportional modes was associated with a reduction in weaning failure (RR 0.44; 95% CI 0.26–0.75; p = 0.003; PAV—three studies) and duration of mechanical ventilation (WMD − 1.78 days; 95% CI − 3.24 to − 0.32; p = 0.017; PAV—three studies, and NAVA—two studies). Reduced duration of mechanical ventilation was found with PAV but not with NAVA.

Conclusion

The use of proportional modes was associated with a reduction in the incidence with AI > 10%, weaning failure and duration of mechanical ventilation, compared with PSV. However, reduced weaning failure and duration of mechanical ventilation were found with only PAV. Due to a significant heterogeneity among studies and an insufficient number of studies, further investigation seems warranted to better understand the impact of proportional modes.

Clinical trial registration PROSPERO registration number, CRD42017059791. Registered 20 March 2017

Electronic supplementary material

The online version of this article (10.1186/s13613-018-0470-y) contains supplementary material, which is available to authorized users.

Respiratory and Peripheral Muscle Assessment in the Intensive Care Unit

Atrophy and weakness of the respiratory and peripheral muscles is a common problem in the intensive care unit (ICU). It is difficult to diagnose, particularly in the early stages of critical disease. Consequently, many cases are detected only in advanced stages, for example, when difficulties in mechanical ventilation weaning are encountered. The aim of this review is to describe the main tools that are currently available for evaluation of peripheral and respiratory muscles in the ICU. Techniques of varying complexity and specificity are discussed, and particular emphasis is placed on those with greater relevance in daily clinical practice, such as ultrasound.

Pulmonary Ultrasound and Diaphragmatic Shortening Fraction Combined Analysis for Extubation-Failure-Prediction in Critical Care Patients

INTRODUCTION

Invasive respiratory support is a cornerstone of Critical Care Medicine, however, protocols for withdrawal of mechanical ventilation are still far from perfect. Failure to extubation occurs in up to 20% of patients, despite a successful spontaneous breathing trial (SBT).

METHODS

We prospectively included ventilated patients admitted to medical and surgical intensive care unit in a university hospital in northern Mexico. At the end of a successful SBT, we measured diaphragmatic shortening fraction (DSF) by the formula: diaphragmatic thickness at the end of inspiration - diaphragmatic thickness at the end of expiration/diaphragmatic thickness at the end of expiration×100, and the presence of B-lines in five regions of the right and left lung. The primary objective was to determine whether analysis of DSF combined with pulmonary ultrasound improves prediction of extubation failure.

RESULTS

Eighty-two patients were included, 24 (29.2%) failed to extubation. At univariate analysis, DSF (Youden's J: >30% [sensibility and specificity 62 and 50%, respectively]) and number of B-lines regions (Youden's J: >1 zone [sensibility and specificity 66 and 92%, respectively]) were significant related to extubation failure (area under the curve 0.66 [0.52-0.80] and 0.81 [0.70-0.93], respectively). At the binomial logistic regression, only the number of B-lines regions remains significantly related to extubation failure (OR 5.91 [2.33-14.98], P<.001).

CONCLUSION

In patients with a successfully SBT, the absence of B-lines significantly decreases the probability of extubation failure. Diaphragmatic shortening fraction analysis does not add predictive power over the use of pulmonary ultrasound.

Avoiding Respiratory and Peripheral Muscle Injury During Mechanical Ventilation: Diaphragm-Protective Ventilation and Early Mobilization

Both limb muscle weakness and respiratory muscle weakness are exceedingly common in critically ill patients. Respiratory muscle weakness prolongs ventilator dependence, predisposing to nosocomial complications and death. Limb muscle weakness persists for months after discharge from intensive care and results in poor long-term functional status and quality of life. Major mechanisms of muscle injury include critical illness polymyoneuropathy, sepsis, pharmacologic exposures, metabolic derangements, and excessive muscle loading and unloading. The diaphragm may become weak because of excessive unloading (leading to atrophy) or because of excessive loading (either concentric or eccentric) owing to insufficient ventilator assistance.

Ultrasound assessment of diaphragmatic dysfunction as a predictor of weaning outcome from mechanical ventilation: a systematic review and meta-analysis

OBJECTIVE

The aim of this systematic review was to assess the diaphragmatic dysfunction (DD) as a predictor of weaning outcome.

BACKGROUND

Successful weaning depends on several factors: muscle strength, cardiac, respiratory and metabolic. Acquired weakness in mechanical ventilation is a growing important cause of weaning failure. With the development of ultrasonography, DD can be evaluated with ultrasound in weakness patients to predict weaning outcomes.

METHODS

The Cochrane Library, PubMed, Embase, Ovid Medline, WanFang Data and CNKI were systematically searched from the inception to September 2017. Ultrasound assessment of DD in adult mechanical ventilation patients was included. Two independent investigators assessed study quality in accordance with the Quality Assessment of Diagnostic Accuracy Studies-2 tool. The primary outcome was diaphragmatic thickness and excursion in the weaning success and failure group. The secondary outcome was the influence of DD on weaning outcome.

RESULTS

Eleven studies involving a total of 436 patients were included. There were eight studies comparing diaphragmatic excursion (DE), five comparing the diaphragmatic thickening fraction (DTF) and two comparing DD between groups with and without successful weaning. Overall, the DE or DTF had a pooled sensitivity of 0.85 (95% CI 0.77 to 0.91) and a pooled specificity of 0.74 (95% CI 0.66 to 0.80) for predicting weaning success. There was high heterogeneity among the included studies (I²=80%; p=0.0006). The rate of weaning failure was significantly increased in patients with DD (OR 8.82; 95% CI 3.51 to 22.13; p<0.00001).

CONCLUSIONS

Both DE and DTF showed good diagnostic performance to predict weaning outcomes in spite of limitations included high heterogeneity among the studies. DD was found to be a predictor of weaning failure in critically ill patients.

Estimation of the diaphragm neuromuscular efficiency index in mechanically ventilated critically ill patients

Background

Diaphragm dysfunction develops frequently in ventilated intensive care unit (ICU) patients. Both disuse atrophy (ventilator over-assist) and high respiratory muscle effort (ventilator under-assist) seem to be involved. A strong rationale exists to monitor diaphragm effort and titrate support to maintain respiratory muscle activity within physiological limits. Diaphragm electromyography is used to quantify breathing effort and has been correlated with transdiaphragmatic pressure and esophageal pressure. The neuromuscular efficiency index (NME) can be used to estimate inspiratory effort, however its repeatability has not been investigated yet. Our goal is to evaluate NME repeatability during an end-expiratory occlusion (NMEoccl) and its use to estimate the pressure generated by the inspiratory muscles (Pmus).

Methods

This is a prospective cohort study, performed in a medical-surgical ICU. A total of 31 adult patients were included, all ventilated in neurally adjusted ventilator assist (NAVA) mode with an electrical activity of the diaphragm (EAdi) catheter in situ. At four time points within 72 h five repeated end-expiratory occlusion maneuvers were performed. NMEoccl was calculated by delta airway pressure (ΔPaw)/ΔEAdi and was used to estimate Pmus. The repeatability coefficient (RC) was calculated to investigate the NMEoccl variability.

Results

A total number of 459 maneuvers were obtained. At time T = 0 mean NMEoccl was 1.22 ± 0.86 cmH₂O/μV with a RC of 82.6%. This implies that when NMEoccl is 1.22 cmH₂O/μV, it is expected with a probability of 95% that the subsequent measured NMEoccl will be between 2.22 and 0.22 cmH2O/μV. Additional EAdi waveform analysis to correct for non-physiological appearing waveforms, did not improve NMEoccl variability. Selecting three out of five occlusions with the lowest variability reduced the RC to 29.8%.

Conclusions

Repeated measurements of NMEoccl exhibit high variability, limiting the ability of a single NMEoccl maneuver to estimate neuromuscular efficiency and therefore the pressure generated by the inspiratory muscles based on EAdi.

Electronic supplementary material

The online version of this article (10.1186/s13054-018-2172-0) contains supplementary material, which is available to authorized users.

Risk factors and outcomes for airway failure versus non-airway failure in the intensive care unit: a multicenter observational study of 1514 extubation procedures

BACKGROUND

Patients liberated from invasive mechanical ventilation are at risk of extubation failure, including inability to breathe without a tracheal tube (airway failure) or without mechanical ventilation (non-airway failure). We sought to identify respective risk factors for airway failure and non-airway failure following extubation.

METHODS

The primary endpoint of this prospective, observational, multicenter study in 26 intensive care units was extubation failure, defined as need for reintubation within 48 h following extubation. A multinomial logistic regression model was used to identify risk factors for airway failure and non-airway failure.

RESULTS

Between 1 December 2013 and 1 May 2015, 1514 patients undergoing extubation were enrolled. The extubation-failure rate was 10.4% (157/1514), including 70/157 (45%) airway failures, 78/157 (50%) non-airway failures, and 9/157 (5%) mixed airway and non-airway failures. By multivariable analysis, risk factors for extubation failure were either common to airway failure and non-airway failure: intubation for coma (OR 4.979 (2.797-8.864), P < 0.0001 and OR 2.067 (1.217-3.510), P = 0.003, respectively, intubation for acute respiratory failure (OR 3.395 (1.877-6.138), P < 0.0001 and OR 2.067 (1.217-3.510), P = 0.007, respectively, absence of strong cough (OR 1.876 (1.047-3.362), P = 0.03 and OR 3.240 (1.786-5.879), P = 0.0001, respectively, or specific to each specific mechanism: female gender (OR 2.024 (1.187-3.450), P = 0.01), length of ventilation > 8 days (OR 1.956 (1.087-3.518), P = 0.025), copious secretions (OR 4.066 (2.268-7.292), P < 0.0001) were specific to airway failure, whereas non-obese status (OR 2.153 (1.052-4.408), P = 0.036) and sequential organ failure assessment (SOFA) score ≥ 8 (OR 1.848 (1.100-3.105), P = 0.02) were specific to non-airway failure. Both airway failure and non-airway failure were associated with ICU mortality (20% and 22%, respectively, as compared to 6% in patients with extubation success, P < 0.0001).

CONCLUSIONS

Specific risk factors have been identified, allowing us to distinguish between risk of airway failure and non-airway failure. The two conditions will be managed differently, both for prevention and curative strategies.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT 02450669 . Registered on 21 May 2015.

Diaphragm Weakness in the Critically Ill: Basic Mechanisms Reveal Therapeutic Opportunities

The diaphragm is the primary muscle of inspiration. Its capacity to respond to the load imposed by pulmonary disease is a major determining factor both in the onset of ventilatory failure and in the ability to successfully separate patients from ventilator support. It has recently been established that a very large proportion of critically ill patients exhibit major weakness of the diaphragm, which is associated with poor clinical outcomes. The two greatest risk factors for the development of diaphragm weakness in critical illness are the use of mechanical ventilation and the presence of sepsis. Loss of force production by the diaphragm under these conditions is caused by a combination of defective contractility and reduced diaphragm muscle mass. Importantly, many of the same molecular mechanisms are implicated in the diaphragm dysfunction associated with both mechanical ventilation and sepsis. This review outlines the primary cellular mechanisms identified thus far at the nexus of diaphragm dysfunction associated with mechanical ventilation and/or sepsis, and explores the potential for treatment or prevention of diaphragm weakness in critically ill patients through therapeutic manipulation of these final common pathway targets.

Positive End-Expiratory Pressure Ventilation Induces Longitudinal Atrophy in Diaphragm Fibers

RATIONALE

Diaphragm weakness in critically ill patients prolongs ventilator dependency and duration of hospital stay and increases mortality and healthcare costs. The mechanisms underlying diaphragm weakness include cross-sectional fiber atrophy and contractile protein dysfunction, but whether additional mechanisms are at play is unknown.

OBJECTIVES

To test the hypothesis that mechanical ventilation with positive end-expiratory pressure (PEEP) induces longitudinal atrophy by displacing the diaphragm in the caudal direction and reducing the length of fibers.

METHODS

We studied structure and function of diaphragm fibers of mechanically ventilated critically ill patients and mechanically ventilated rats with normal and increased titin compliance.

MEASUREMENTS AND MAIN RESULTS

PEEP causes a caudal movement of the diaphragm, both in critically ill patients and in rats, and this caudal movement reduces fiber length. Diaphragm fibers of 18-hour mechanically ventilated rats (PEEP of 2.5 cm H2O) adapt to the reduced length by absorbing serially linked sarcomeres, the smallest contractile units in muscle (i.e., longitudinal atrophy). Increasing the compliance of titin molecules reduces longitudinal atrophy.

CONCLUSIONS

Mechanical ventilation with PEEP results in longitudinal atrophy of diaphragm fibers, a response that is modulated by the elasticity of the giant sarcomeric protein titin. We postulate that longitudinal atrophy, in concert with the aforementioned cross-sectional atrophy, hampers spontaneous breathing trials in critically ill patients: during these efforts, end-expiratory lung volume is reduced, and the shortened diaphragm fibers are stretched to excessive sarcomere lengths. At these lengths, muscle fibers generate less force, and diaphragm weakness ensues.

Prolonged mechanical ventilation worsens sepsis-induced diaphragmatic dysfunction in the rat

Background

Short-term mechanical ventilation (MV) protects against sepsis-induced diaphragmatic dysfunction. Prolonged MV induces diaphragmatic dysfunction in non-septic animals, but few reports describe the effects of prolonged MV in sepsis. We hypothesized that prolonged MV is not protective but worsens the diaphragmatic dysfunction induced by a mild sepsis, because MV and sepsis share key signaling mechanisms, such as cytokine upregulation.

Method

We studied the impact of prolonged MV (12 h) in four groups (n = 8) of male Wistar rats: 1) endotoxemia induced by intraperitoneal injection of Escherichia coli lipopolysaccharide, 2) MV without endotoxemia, 3) combination of endotoxemia and MV and 4) sham control. Diaphragm mechanical performance, pro-inflammatory cytokine concentrations (Tumor Necrosis Factor-α, Interleukin-1β, Interleukin-6) in plasma were measured.

Results

Prolonged MV and sepsis independtly reduced maximum diaphragm force (-27%, P = 0.003; -37%, P<0.001; respectively). MV and sepsis acted additively to further decrease diaphragm force (-62%, P<0.001). Similar results were observed for diaphragm kinetics (maximum lengthening velocity -47%, P<0.001). Sepsis and MV reduced diaphragm cross sectional area of type I and IIx fibers, which was further increased by the combination of sepsis and MV (all P<0.05). Sepsis and MV were individually associated with the presence of a robust perimysial inflammatory infiltrate, which was more marked when sepsis and MV were both present (all P<0.05). Sepsis and, to a lesser extent, MV increased proinflammatory cytokine production in plasma and diaphragm (all P<0.05); proinflammatory cytokine expression in plasma was increased further by the combination of sepsis and MV (all P<0.05). Maximum diaphragm force correlated negatively with plasma and diaphragmatic cytokine production (all p<0.05).

Conclusions

Prolonged (12 h) MV exacerbated sepsis-induced decrease in diaphragm performance. Systemic and diaphragmatic overproduction of pro-inflammatory cytokines may contribute to diaphragm weakness.

Inspiratory muscle training for intensive care patients: A multidisciplinary practical guide for clinicians

OBJECTIVES

To describe a multidisciplinary approach to inspiratory muscle training (IMT) for patients in the intensive care unit (ICU).

BACKGROUND

Inspiratory muscle weakness is a known consequence of prolonged mechanical ventilation, and there is emerging evidence that specific IMT can ameliorate this weakness. However, IMT is not yet standard practice in many ICUs, possibly because of the wide variety of methods reported and a lack of published practical guidelines. While the optimal parameters for IMT are yet to be established, we share our detailed methodology which has been shown to be safe in selected ventilator-dependent patients and is the only approach which has been shown to increase quality of life in ICU patients.

METHODS

Patients who have experienced invasive mechanical ventilation for at least 7 days can commence IMT in either the ventilator-dependent phase or when weaned from mechanical ventilation. Intensity should be prescribed based on maximum inspiratory pressure, which is measurable through the tracheostomy or endotracheal tube via the ventilator or a respiratory pressure meter. Using a removable threshold device, we recommend high-intensity training (5 sets of 6 breaths at a minimum of 50% of maximum inspiratory pressure) performed once per day, supervised by the physiotherapist, with intensity increased daily such that patients can only just complete the 6th breath in each set.

RESULTS

Using this high-intensity approach, IMT is likely to improve not only inspiratory muscle strength but also quality of life in patients recently weaned from mechanical ventilation of 7 days' duration or longer. Effective IMT requires a multidisciplinary approach to maximise feasibility, with doctors, nurses, and therapists working closely to optimise conditions for successful IMT.

CONCLUSIONS

This multidisciplinary approach to implement IMT in ICU patients should assist clinicians in translating best-available evidence into practice, with the potential to enhance patient recovery.

Using twitch tracheal airway pressure, negative inhale forced pressure, and Medical Research Council score to guide weaning from mechanical ventilation

Background

Weaning from mechanical ventilation (MV) is an important and universal issue in critically ill patients, with no consensus that predicts weaning success. Twitch tracheal airway pressure (TwPtr) may be a more objective indicator of diaphragm function. The present study evaluated TwPtr relative to negative inspiratory force (NIF) or Medical Research Council (MRC) score, for predicting success of weaning from MV.

Methods

From December 2015 to March 2017, 62 patients were included who received invasive MV >48 hours and then underwent a test for spontaneous breathing. The NIF and MRC score were sequentially determined. The TwPtr measurement was performed via magnetic stimulation of the neck phrenic nerve.

Results

Weaning success was achieved by 54 patients (87.1%), including 30, 12, and 12 patients who experienced simple, difficult, and prolonged weaning, respectively. The areas under receiver operating characteristic curves (AUCs) for NIF, MRC score, and TwPtr were 0.778, 0.560, and 0.792. When TwPtr was combined with NIF, the sensitivity and specificity of weaning success were 96.3% and 75.0%, and AUC was 0.807. In the weaning success group, after correction for age, the AUC of TwPtr was 0.878, which differentiated the simple weaning from non-simple group.

Conclusions

TwPtr was superior to either NIF or MRC score for differentiating patients in the simple weaning group from those patients who experienced difficult, prolonged, or failed weaning. TwPtr combined with NIF may be used to predict weaning success better than the MRC score alone.

Muscle metabolism

PURPOSE OF REVIEW

To review the recent findings on metabolic derangements leading to loss of muscle mass and function.

RECENT FINDINGS

Several recent studies investigated methods to assess muscle mass and function and its clinical relevance. These are also included. A few studies confirm that a low muscle mass is related to a worse outcome but also a compromised muscle function at discharge is related to long-term survival. A low quality of muscle assessed by the density of muscle from a computed tomography scan is related to mortality. For the metabolic derangements, a compromised handling of calcium is present in muscle of animal models and might be causing a decreased muscle function in patients. Transcriptomics analyses of muscle post-ICU indicated an upregulation of regenerative pathways, but still muscle mass is not recovering in most patients. This could be due to an impairment regenerative capacity due to satellite cells dysfunction.

SUMMARY

Muscle mass and function are related to outcome. New finding show that not only muscle mass but also muscle quality is important, that a compromised handling of calcium might be involved in muscle weakness and that regaining muscle could be compromised due to a defective regenerative capacity of satellite cells.

Coordination of Pharyngeal and Laryngeal Swallowing Events During Single Liquid Swallows After Oral Endotracheal Intubation for Patients with Acute Respiratory Distress Syndrome

To evaluate timing and duration differences in airway protection and esophageal opening after oral intubation and mechanical ventilation for acute respiratory distress syndrome (ARDS) survivors versus age-matched healthy volunteers. Orally intubated adult (≥ 18 years old) patients receiving mechanical ventilation for ARDS were evaluated for swallowing impairments via a videofluoroscopic swallow study (VFSS) during usual care. Exclusion criteria were tracheostomy, neurological impairment, and head and neck cancer. Previously recruited healthy volunteers (n = 56) served as age-matched controls. All subjects were evaluated using 5-ml thin liquid barium boluses. VFSS recordings were reviewed frame-by-frame for the onsets of 9 pharyngeal and laryngeal events during swallowing. Eleven patients met inclusion criteria, with a median (interquartile range [IQR]) intubation duration of 14 (9, 16) days, and VFSSs completed a median of 5 (4, 13) days post-extubation. After arrival of the bolus in the pharynx, ARDS patients achieved maximum laryngeal closure a median (IQR) of 184 (158, 351) ms later than age-matched, healthy volunteers (p < 0.001) and it took longer to achieve laryngeal closure with a median (IQR) difference of 151 (103, 217) ms (p < 0.001), although there was no significant difference in duration of laryngeal closure. Pharyngoesophageal segment opening was a median (IQR) of - 116 (- 183, 1) ms (p = 0.004) shorter than in age-matched, healthy controls. Evaluation of swallowing physiology after oral endotracheal intubation in ARDS patients demonstrates slowed pharyngeal and laryngeal swallowing timing, suggesting swallow-related muscle weakness. These findings may highlight specific areas for further evaluation and potential therapeutic intervention to reduce post-extubation aspiration.

Diaphragm function and weaning from mechanical ventilation: an ultrasound and phrenic nerve stimulation clinical study

Background

Diaphragm dysfunction is defined by a value of twitch tracheal pressure in response to magnetic phrenic stimulation (twitch pressure) amounting to less than 11 cmH₂O. This study assessed whether this threshold or a lower one would predict accurately weaning failure from mechanical ventilation. Twitch pressure was compared to ultrasound measurement of diaphragm function.

Methods

In patients undergoing a first spontaneous breathing trial, diaphragm function was evaluated by twitch pressure and by diaphragm ultrasound (thickening fraction). Receiver operating characteristics curves were computed to determine the best thresholds predicting failure of spontaneous breathing trial.

Results

Seventy-six patients were evaluated, 48 (63%) succeeded and 28 (37%) failed the spontaneous breathing trial. The optimal thresholds of twitch pressure and thickening fraction to predict failure of the spontaneous breathing trial were, respectively, 7.2 cmH₂O and 25.8%, respectively. The receiver operating characteristics curves were 0.80 (95% CI 0.70–0.89) for twitch pressure and 0.82 (95% CI 0.73–0.93) for thickening fraction. Both receiver operating characteristics curves were similar (p = 0.83). A twitch pressure value lower than 11 cmH₂O (the traditional cutoff for diaphragm dysfunction) predicted failure of the spontaneous breathing trial with a sensitivity of 89% (95% CI 72–98%) and a specificity of 45% (95% CI 30–60%).

Conclusions

Failure of spontaneous breathing trial can be predicted with a lower value of twitch pressure than the value defining diaphragm dysfunction. Twitch pressure and thickening fraction had similar strong performance in the prediction of failure of the spontaneous breathing trial.

Electronic supplementary material

The online version of this article (10.1186/s13613-018-0401-y) contains supplementary material, which is available to authorized users.

Impact of limb weakness on extubation failure after planned extubation in medical patients

BACKGROUND AND OBJECTIVE

Limb muscle weakness is associated with difficult weaning. However, there are limited data on extubation failure. The objective of this cohort study was to evaluate the association between limb muscle weakness according to the Medical Research Council (MRC) scale and extubation failure rates among patients in a medical intensive care unit (ICU).

METHODS

All consecutive medical ICU patients who were mechanically ventilated for more than 24 h and who were weaned according to protocol were prospectively registered, and limb muscle weakness was assessed using the MRC scale on the day of planned extubation. Association of limb muscle weakness with extubation failure within 48 h following planned extubation was evaluated with logistic regression analysis.

RESULTS

Over the study period, 377 consecutive patients underwent planned extubation through a standardized weaning process. Extubation failure occurred in 106 (28.1%) patients. Median scores on the MRC scale for four limbs were lower in patients with extubation failure (14, interquartile range (IQR) 12-16) than in patients without extubation failure (16, IQR 12-18; P = 0.024). In addition, extubation failure rates decreased significantly with increasing quartiles of MRC scores (P for trend <0.001). In multivariable analysis, MRC scores ≤10 points were independently associated with extubation failure within 48 h (adjusted OR 2.131, 95% CI: 1.071-4.240, P = 0.031).

CONCLUSION

Limb muscle weakness assessed on the day of extubation was found to be independently associated with higher extubation failure rates within 48 h following planned extubation in medical patients.

Effect of hypercapnia on respiratory and peripheral skeletal muscle loss during critical illness - A pilot study

INTRODUCTION

Critical illness has profound effects on muscle strength and long-term physical morbidity. However, there remains a paucity of evidence for the aetiology of critical illness related weakness. Recent animal model research identified that hypercapnia may reduce the rate of muscle loss. The aim of this study was to determine the effect of hypercapnia on respiratory and peripheral skeletal muscle in patients with critical illness.

METHODS

A pilot observational study of mechanically ventilated critically ill patients at a tertiary critical care unit who were retrospectively categorised as: 1) Respiratory failure with normocapnia; 2) Respiratory failure with hypercapnia; and 3) brain injury. Diaphragm thickness and quadriceps rectus femoris cross-sectional area (RFCSA) were measured using ultrasound imaging at baseline and at days 3, 5, 7 and 10 of mechanical ventilation.

RESULTS

Significant reductions in RFCSA muscle loss were observed for all time-points when compared to baseline [day 10: -14.9%±8.2 p< 0.001], and in diaphragm thickness between baseline and day 7 [day 7: -5.8%±9.5 p=0.029). No correlation was identified between the rate of muscle mass loss in the diaphragm and RFCSA.

CONCLUSION

In this pilot study, peripheral skeletal muscle weakness occurred early and rapidly within the critical care population, irrespective of carbon dioxide levels.

Diaphragm dysfunction during weaning from mechanical ventilation: an underestimated phenomenon with clinical implications

This article is one of ten reviews selected from the Annual Update in Intensive Care and Emergency Medicine 2018. Other selected articles can be found online at https://www.biomedcentral.com/collections/annualupdate2018. Further information about the Annual Update in Intensive Care and Emergency Medicine is available from http://www.springer.com/series/8901.

Impact of sleep alterations on weaning duration in mechanically ventilated patients: a prospective study

Sleep is markedly altered in intensive care unit (ICU) patients and may alter respiratory performance. Our objective was to assess the impact of sleep alterations on weaning duration.

We conducted a prospective physiological study at a French teaching hospital. ICU patients intubated for at least 24 h and difficult to wean were included. Complete polysomnography (PSG) was performed after the first spontaneous breathing trial failure. Presence of atypical sleep, duration of sleep stages, particularly rapid eye movement (REM) sleep, and electroencephalogram (EEG) reactivity at eyes opening were assessed by a neurologist.

20 out of 45 patients studied (44%) had atypical sleep that could not be classified according to the standard criteria. Duration of weaning between PSG and extubation was significantly longer in patients with atypical sleep (median (interquartile range) 5 (2–8) versus 2 (1–2) days; p=0.001) and in those with no REM sleep compared with the others. Using multivariate logistic regression analysis, atypical sleep remained independently associated with prolonged weaning (>48 h after PSG). Altered EEG reactivity at eyes opening was a good predictor of atypical sleep.

Our results suggest for the first time that brain dysfunction may have an influence on the ability to breathe spontaneously.

Diaphragmatic Palsy

The diaphragm is the primary muscle of respiration, and its weakness can lead to respiratory failure. Diaphragmatic palsy can be caused by various causes. Injury to the phrenic nerve during thoracic surgeries is the most common cause for diaphragmatic palsy. Depending on the cause, the symptoms of diaphragmatic palsies vary from completely asymptomatic to disabling dyspnea requiring mechanical ventilation. On pulmonary function tests, there will be a decrease in the maximum respiratory muscle power. Spirometry shows reduced lung functions and a significant drop of lung function in supine position is typical of diaphragmatic palsy. Diaphragmatic movements with respiration can be directly visualized by fluoroscopic examination. Currently, this test is being replaced by bedside thoracic ultrasound examination, looking at the diaphragmic excursion with deep breathing or sniffing. This test is found to be equally efficient, and without risks of ionizing radiation of fluoroscope. Treatment of diaphragmatic palsy depends on the cause. Surgical approach of repair of diaphragm or nonsurgical approach of noninvasive ventilation has been tried with good success. Overall prognosis of diaphragmatic palsy is good, except when it is related to neuromuscular degeneration conditions.

Reliability of respiratory pressure measurements in ventilated and non-ventilated patients in ICU: an observational study

Background

Assessment of maximum respiratory pressures is a common practice in intensive care because it can predict the success of weaning from ventilation. However, the reliability of measurements through an intubation catheter has not been compared with standard measurements. The aim of this study was to compare maximum respiratory pressures measured through an intubation catheter with the same measurements using a standard mouthpiece in extubated patients.

Methods

A prospective observational study was carried out in adults who had been under ventilation for at least 24 h and for whom extubation was planned. Maximal respiratory pressure measurements were carried out before and 24 h following extubation.

Results

Ninety patients were included in the analyses (median age: 61.5 years, median SAPS2 score: 42.5 and median duration of ventilation: 7 days). Maximum respiratory pressures measured through the intubation catheter were as reliable as measurements through a standard mouthpiece (difference in maximal inspiratory pressure: mean bias = − 2.43 ± 14.43 cmH₂O and difference in maximal expiratory pressure: mean bias = 1.54 ± 23.2 cmH₂O).

Conclusion

Maximum respiratory pressures measured through an intubation catheter were reliable and similar to standard measures.

Clinical trial registration Retrospectively Registered in ClinicalTrials.gov (NCT02363231).

Diaphragm Atrophy and Weakness in the Absence of Mitochondrial Dysfunction in the Critically Ill

RATIONALE

The clinical significance of diaphragm weakness in critically ill patients is evident: it prolongs ventilator dependency and increases morbidity, duration of hospital stay, and health care costs. The mechanisms underlying diaphragm weakness are unknown, but might include mitochondrial dysfunction and oxidative stress.

OBJECTIVES

We hypothesized that weakness of diaphragm muscle fibers in critically ill patients is accompanied by impaired mitochondrial function and structure, and by increased markers of oxidative stress.

METHODS

To test these hypotheses, we studied contractile force, mitochondrial function, and mitochondrial structure in diaphragm muscle fibers. Fibers were isolated from diaphragm biopsies of 36 mechanically ventilated critically ill patients and compared with those isolated from biopsies of 27 patients with suspected early-stage lung malignancy (control subjects).

MEASUREMENTS AND MAIN RESULTS

Diaphragm muscle fibers from critically ill patients displayed significant atrophy and contractile weakness, but lacked impaired mitochondrial respiration and increased levels of oxidative stress markers. Mitochondrial energy status and morphology were not altered, despite a lower content of fusion proteins.

CONCLUSIONS

Critically ill patients have manifest diaphragm muscle fiber atrophy and weakness in the absence of mitochondrial dysfunction and oxidative stress. Thus, mitochondrial dysfunction and oxidative stress do not play a causative role in the development of atrophy and contractile weakness of the diaphragm in critically ill patients.

Recovery after critical illness: putting the puzzle together-a consensus of 29

In this review, we seek to highlight how critical illness and critical care affect longer-term outcomes, to underline the contribution of ICU delirium to cognitive dysfunction several months after ICU discharge, to give new insights into ICU acquired weakness, to emphasize the importance of value-based healthcare, and to delineate the elements of family-centered care. This consensus of 29 also provides a perspective and a research agenda about post-ICU recovery.

The Intersection of Aging Biology and the Pathobiology of Lung Diseases: A Joint NHLBI/NIA Workshop

Death from chronic lung disease is increasing and chronic obstructive pulmonary disease has become the third leading cause of death in the United States in the past decade. Both chronic and acute lung diseases disproportionately affect elderly individuals, making it likely that these diseases will become more frequent and severe as the worldwide population ages. Chronic lung diseases are associated with substantial morbidity, frequently resulting in exercise limiting dyspnea, immobilization, and isolation. Therefore, effective strategies to prevent or treat lung disease are likely to increase healthspan as well as life span. This review summarizes the findings of a joint workshop sponsored by the NIA and NHLBI that brought together investigators focused on aging and lung biology. These investigators encouraged the use of genetic systems and aged animals in the study of lung disease and the development of integrative systems-based platforms that can dynamically incorporate data sets that describe the genomics, transcriptomics, epigenomics, metabolomics, and proteomics of the aging lung in health and disease. Further research was recommended to integrate benchmark biological hallmarks of aging in the lung with the pathobiology of acute and chronic lung diseases with divergent pathologies for which advanced age is the most important risk factor.

Critical illness-associated diaphragm weakness

Diaphragm weakness is highly prevalent in critically ill patients. It may exist prior to ICU admission and may precipitate the need for mechanical ventilation but it also frequently develops during the ICU stay. Several risk factors for diaphragm weakness have been identified; among them sepsis and mechanical ventilation play central roles. We employ the term critical illness-associated diaphragm weakness to refer to the collective effects of all mechanisms of diaphragm injury and weakness occurring in critically ill patients. Critical illness-associated diaphragm weakness is consistently associated with poor outcomes including increased ICU mortality, difficult weaning, and prolonged duration of mechanical ventilation. Bedside techniques for assessing the respiratory muscles promise to improve detection of diaphragm weakness and enable preventive or curative strategies. Inspiratory muscle training and pharmacological interventions may improve respiratory muscle function but data on clinical outcomes remain limited.

Diaphragm Dysfunction in Critical Illness

The diaphragm is the major muscle of inspiration, and its function is critical for optimal respiration. Diaphragmatic failure has long been recognized as a major contributor to death in a variety of systemic neuromuscular disorders. More recently, it is increasingly apparent that diaphragm dysfunction is present in a high percentage of critically ill patients and is associated with increased morbidity and mortality. In these patients, diaphragm weakness is thought to develop from disuse secondary to ventilator-induced diaphragm inactivity and as a consequence of the effects of systemic inflammation, including sepsis. This form of critical illness-acquired diaphragm dysfunction impairs the ability of the respiratory pump to compensate for an increased respiratory workload due to lung injury and fluid overload, leading to sustained respiratory failure and death. This review examines the presentation, causes, consequences, diagnosis, and treatment of disorders that result in acquired diaphragm dysfunction during critical illness.

Mechanical Ventilation: State of the Art

Mechanical ventilation is the most used short-term life support technique worldwide and is applied daily for a diverse spectrum of indications, from scheduled surgical procedures to acute organ failure. This state-of-the-art review provides an update on the basic physiology of respiratory mechanics, the working principles, and the main ventilatory settings, as well as the potential complications of mechanical ventilation. Specific ventilatory approaches in particular situations such as acute respiratory distress syndrome and chronic obstructive pulmonary disease are detailed along with protective ventilation in patients with normal lungs. We also highlight recent data on patient-ventilator dyssynchrony, humidified high-flow oxygen through nasal cannula, extracorporeal life support, and the weaning phase. Finally, we discuss the future of mechanical ventilation, addressing avenues for improvement.

The ICM research agenda on intensive care unit-acquired weakness

We present areas of uncertainty concerning intensive care unit-acquired weakness (ICUAW) and identify areas for future research. Age, pre-ICU functional and cognitive state, concurrent illness, frailty, and health trajectories impact outcomes and should be assessed to stratify patients. In the ICU, early assessment of limb and diaphragm muscle strength and function using nonvolitional tests may be useful, but comparison with established methods of global and specific muscle strength and physical function and determination of their reliability and normal values would be important to advance these techniques. Serial measurements of limb and respiratory muscle strength, and systematic screening for dysphagia, would be helpful to clarify if and how weakness of these muscle groups is independently associated with outcome. ICUAW, delirium, and sedatives and analgesics may interact with each other, amplifying the effects of each individual factor. Reduced mobility in patients with hypoactive delirium needs investigations into dysfunction of central and peripheral nervous system motor pathways. Interventional nutritional studies should include muscle mass, strength, and physical function as outcomes, and prioritize elucidation of mechanisms. At follow-up, ICU survivors may suffer from prolonged muscle weakness and wasting and other physical impairments, as well as fatigue without demonstrable weakness on examination. Further studies should evaluate the prevalence and severity of fatigue in ICU survivors and define its association with psychiatric disorders, pain, cognitive impairment, and axonal loss. Finally, methodological issues, including accounting for baseline status, handling of missing data, and inclusion of patient-centered outcome measures should be addressed in future studies.

Transcriptome analysis reveals long intergenic non-coding RNAs involved in skeletal muscle growth and development in pig

Long intergenic non-coding RNAs (lincRNAs) play essential roles in numerous biological processes and are widely studied. The skeletal muscle is an important tissue that plays an essential role in individual movement ability. However, lincRNAs in pig skeletal muscles are largely undiscovered and their biological functions remain elusive. In this study, we assembled transcriptomes using RNA-seq data published in previous studies of our laboratory group and identified 323 lincRNAs in porcine leg muscle. We found that these lincRNAs have shorter transcript length, fewer exons and lower expression level than protein-coding genes. Gene ontology and pathway analyses indicated that many potential target genes (PTGs) of lincRNAs were involved in skeletal-muscle-related processes, such as muscle contraction and muscle system process. Combined our previous studies, we found a potential regulatory mechanism in which the promoter methylation of lincRNAs can negatively regulate lincRNA expression and then positively regulate PTG expression, which can finally result in abnormal phenotypes of cloned piglets through a certain unknown pathway. This work detailed a number of lincRNAs and their target genes involved in skeletal muscle growth and development and can facilitate future studies on their roles in skeletal muscle growth and development.

Prevalence and Impact on Weaning of Pleural Effusion at the Time of Liberation from Mechanical Ventilation: A Multicenter Prospective Observational Study

BACKGROUND

Pleural effusion is frequent in intensive care unit patients, but its impact on the outcome of weaning remains unknown.

METHODS

In a prospective study performed in three intensive care units, pleural ultrasound was performed at the first spontaneous breathing trial to detect and quantify pleural effusion (small, moderate, and large). Weaning failure was defined by a failed spontaneous breathing trial and/or extubation requiring any form of ventilatory support within 48 h. The primary endpoint was the prevalence of pleural effusion according to weaning outcome.

RESULTS

Pleural effusion was detected in 51 of 136 (37%) patients and was quantified as moderate to large in 18 (13%) patients. As compared to patients with no or small pleural effusion, their counterparts were more likely to have chronic renal failure (39 vs. 7%; P = 0.01), shock as the primary reason for admission (44 vs. 19%; P = 0.02), and a greater weight gain (+4 [0 to 7] kg vs. 0 [-1 to 5] kg; P = 0.02). The prevalence of pleural effusion was similar in weaning success and weaning failure patients (odds ratio, 1.23; 95% CI, 0.61 to 2.49; P = 0.56), as was the prevalence of moderate to large pleural effusion (odds ratio, 0.89; 95% CI, 0.33 to 2.41; P = 1.00). Duration of mechanical ventilation and intensive care unit length of stay were similar between patients with no or small pleural effusion and those with moderate to large pleural effusion.

CONCLUSIONS

Significant pleural effusion was observed in 13% of patients at the time of liberation from mechanical ventilation and was not associated with an alteration of weaning outcome. (ANESTHESIOLOGY 2017; 126:1107-15).

Ultrasound evaluation of diaphragm function in mechanically ventilated patients: comparison to phrenic stimulation and prognostic implications

RATIONALE

In intensive care unit (ICU) patients, diaphragm dysfunction is associated with adverse clinical outcomes. Ultrasound measurements of diaphragm thickness, excursion (EXdi) and thickening fraction (TFdi) are putative estimators of diaphragm function, but have never been compared with phrenic nerve stimulation. Our aim was to describe the relationship between these variables and diaphragm function evaluated using the change in endotracheal pressure after phrenic nerve stimulation (Ptr,stim), and to compare their prognostic value.

METHODS

Between November 2014 and June 2015, Ptr,stim and ultrasound variables were measured in mechanically ventilated patients <24 hours after intubation ('initiation of mechanical ventilation (MV)', under assist-control ventilation, ACV) and at the time of switch to pressure support ventilation ('switch to PSV'), and compared using Spearman's correlation and receiver operating characteristic curve analysis. Diaphragm dysfunction was defined as Ptr,stim <11 cm H₂O.

RESULTS

112 patients were included. At initiation of MV, Ptr,stim was not correlated to diaphragm thickness (p=0.28), EXdi (p=0.66) or TFdi (p=0.80). At switch to PSV, TFdi and EXdi were respectively very strongly and moderately correlated to Ptr,stim, (r=0.87, p<0.001 and 0.45, p=0.001), but diaphragm thickness was not (p=0.45). A TFdi <29% could reliably identify diaphragm dysfunction (sensitivity and specificity of 85% and 88%), but diaphragm thickness and EXdi could not. This value was associated with increased duration of ICU stay and MV, and mortality.

CONCLUSIONS

Under ACV, diaphragm thickness, EXdi and TFdi were uncorrelated to Ptr,stim. Under PSV, TFdi was strongly correlated to diaphragm strength and both were predictors of remaining length of MV and ICU and hospital death.

Intensive Early Rehabilitation in the Intensive Care Unit for Liver Transplant Recipients: A Randomized Controlled Trial

OBJECTIVE

To validate the feasibility and tolerance of an intensive rehabilitation protocol initiated during the postoperative period in an intensive care unit (ICU) in liver transplant recipients.

DESIGN

Prospective randomized study.

SETTING

ICU.

PARTICIPANTS

Liver transplant recipients over a period of 1 year (N=40).

INTERVENTIONS

The "usual treatment group" (n=20), which benefited from the usual treatment applied in the ICU (based on physician prescription for the physiotherapist, with one session a day), and the experimental group (n=20), which followed a protocol of early and intensive rehabilitation (based on a written protocol validated by physicians and an evaluation by physiotherapist, with 2 sessions a day), were compared.

MAIN OUTCOME MEASURES

Our primary aims were tolerance, assessed from the number of adverse events during rehabilitation sessions, and feasibility, assessed from the number of sessions discontinued.

RESULTS

The results revealed a small percentage of adverse events (1.5% in the usual treatment group vs 1.06% in the experimental group) that were considered to be of low intensity. Patients in the experimental group sat on the edge of their beds sooner (2.6 vs 9.7d; P=.048) and their intestinal transit resumed earlier (5.6 vs 3.7d; P=.015) than patients in the usual treatment group. There was no significant difference between the 2 arms regarding length of stay (LOS), despite a decrease in duration in the experimental group.

CONCLUSIONS

The introduction of an intensive early rehabilitation program for liver transplant recipients was well tolerated and feasible in the ICU. We noted that the different activities proposed were introduced sooner in the experimental group. Moreover, there is a tendency to decreased LOS in the ICU for the experimental group. These results now need to be confirmed by studies on a larger scale.

Diaphragm Dysfunction: Diagnostic Approaches and Management Strategies

The diaphragm is the main inspiratory muscle, and its dysfunction can lead to significant adverse clinical consequences. The aim of this review is to provide clinicians with an overview of the main causes of uni- and bi-lateral diaphragm dysfunction, explore the clinical and physiological consequences of the disease on lung function, exercise physiology and sleep and review the available diagnostic tools used in the evaluation of diaphragm function. A particular emphasis is placed on the clinical significance of diaphragm weakness in the intensive care unit setting and the use of ultrasound to evaluate diaphragmatic action.