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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 .

Mechanical ventilation may have adverse effects on both the lung and the diaphragm. Injury to the lung is mediated by excessive mechanical stress and strain, whereas the diaphragm develops atrophy as a consequence of low respiratory effort and injury in case of excessive effort. The lung and diaphragm-protective mechanical ventilation approach aims to protect both organs simultaneously whenever possible. This review summarizes practical strategies for achieving lung and diaphragm-protective targets at the bedside, focusing on inspiratory and expiratory ventilator settings, monitoring of inspiratory effort or respiratory drive, management of dyssynchrony, and sedation considerations. A number of potential future adjunctive strategies including extracorporeal CO2 removal, partial neuromuscular blockade, and neuromuscular stimulation are also discussed. While clinical trials to confirm the benefit of these approaches are awaited, clinicians should become familiar with assessing and managing patients’ respiratory effort, based on existing physiological principles. To protect the lung and the diaphragm, ventilation and sedation might be applied to avoid excessively weak or very strong respiratory efforts and patient-ventilator dysynchrony.

Respiratory muscle ultrasound is used to evaluate the anatomy and function of the respiratory muscle pump. It is a safe, repeatable, accurate, and non-invasive bedside technique that can be successfully applied in different settings, including general intensive care and the emergency department. Mastery of this technique allows the intensivist to rapidly diagnose and assess respiratory muscle dysfunction in critically ill patients and in patients with unexplained dyspnea. Furthermore, it can be used to assess patient–ventilator interaction and weaning failure in critically ill patients. This paper provides an overview of the basic and advanced principles underlying respiratory muscle ultrasound with an emphasis on the diaphragm. We review different ultrasound techniques useful for monitoring of the respiratory muscle pump and possible therapeutic consequences. Ideally, respiratory muscle ultrasound is used in conjunction with other components of critical care ultrasound to obtain a comprehensive evaluation of the critically ill patient. We propose the ABCDE-ultrasound approach, a systematic ultrasound evaluation of the heart, lungs and respiratory muscle pump, in patients with weaning failure.

Abstract Rationale Intensive care unit (ICU)- and mechanical ventilation (MV)-acquired limb muscle and diaphragm dysfunction may both be associated with longer length of stay and worse outcome. Whether they are two aspects of the same entity or have a different prevalence and prognostic impact remains unclear. Objectives To quantify the prevalence and coexistence of these two forms of ICU-acquired weakness and their impact on outcome. Methods In patients undergoing a first spontaneous breathing trial after at least 24 hours of MV, diaphragm dysfunction was evaluated using twitch tracheal pressure in response to bilateral anterior magnetic phrenic nerve stimulation (a pressure <11 cm H2O defined dysfunction) and ultrasonography (thickening fraction [TFdi] and excursion). Limb muscle weakness was defined as a Medical Research Council (MRC) score less than 48. Measurements and Main Results Seventy-six patients were assessed at their first spontaneous breathing trial: 63% had diaphragm dysfunction, 34% had limb muscle weakness, and 21% had both. There was a significant but weak correlation between MRC score and twitch pressure (ρ = 0.26; P = 0.03) and TFdi (ρ = 0.28; P = 0.01), respectively. Low twitch pressure (odds ratio, 0.60; 95% confidence interval, 0.45–0.79; P < 0.001) and TFdi (odds ratio, 0.84; 95% confidence interval, 0.76–0.92; P < 0.001) were independently associated with weaning failure, but the MRC score was not. Diaphragm dysfunction was associated with higher ICU and hospital mortality, and limb muscle weakness was associated with longer duration of MV and hospital stay. Conclusions Diaphragm dysfunction is twice as frequent as limb muscle weakness and has a direct negative impact on weaning outcome. The two types of muscle weakness have only limited overlap.

RationaleIn 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.MethodsBetween 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.Results112 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.ConclusionsUnder 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.

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.

Abstract Rationale Diaphragm dysfunction worsens outcomes in mechanically ventilated patients, but the clinical impact of potentially preventable changes in diaphragm structure and function caused by mechanical ventilation is unknown. Objectives To determine whether diaphragm atrophy developing during mechanical ventilation leads to prolonged ventilation. Methods Diaphragm thickness was measured daily by ultrasound in adults requiring invasive mechanical ventilation; inspiratory effort was assessed by thickening fraction. The primary outcome was time to liberation from ventilation. Secondary outcomes included complications (reintubation, tracheostomy, prolonged ventilation, or death). Associations were adjusted for age, severity of illness, sepsis, sedation, neuromuscular blockade, and comorbidity. Measurements and Main Results Of 211 patients enrolled, 191 had two or more diaphragm thickness measurements. Thickness decreased more than 10% in 78 patients (41%) by median Day 4 (interquartile range, 3–5). Development of decreased thickness was associated with a lower daily probability of liberation from ventilation (adjusted hazard ratio, 0.69; 95% confidence interval [CI], 0.54–0.87; per 10% decrease), prolonged ICU admission (adjusted duration ratio, 1.71; 95% CI, 1.29–2.27), and a higher risk of complications (adjusted odds ratio, 3.00; 95% CI, 1.34–6.72). Development of increased thickness (n = 47; 24%) also predicted prolonged ventilation (adjusted duration ratio, 1.38; 95% CI, 1.00–1.90). Decreasing thickness was related to abnormally low inspiratory effort; increasing thickness was related to excessive effort. Patients with thickening fraction between 15% and 30% (similar to breathing at rest) during the first 3 days had the shortest duration of ventilation. Conclusions Diaphragm atrophy developing during mechanical ventilation strongly impacts clinical outcomes. Targeting an inspiratory effort level similar to that of healthy subjects at rest might accelerate liberation from ventilation.

Background In patients on mechanical ventilation, positive end-expiratory pressure (PEEP) can decrease cardiac output through a decrease in cardiac preload and/or an increase in right ventricular afterload. Increase in central blood volume by fluid administration or passive leg raising (PLR) may reverse these phenomena through an increase in cardiac preload and/or a reopening of closed lung microvessels. We hypothesized that a transient decrease in PEEP (PEEP-test) may be used as a test to detect volume responsiveness. Methods Mechanically ventilated patients with PEEP ≥ 10 cmH 2 O (“high level”) and without spontaneous breathing were prospectively included. Volume responsiveness was assessed by a positive PLR-test, defined as an increase in pulse-contour-derived cardiac index (CI) during PLR ≥ 10%. The PEEP-test consisted in reducing PEEP from the high level to 5 cmH 2 O for one minute. Pulse-contour-derived CI (PiCCO2) was monitored during PLR and the PEEP-test. Results We enrolled 64 patients among whom 31 were volume responsive. The median increase in CI during PLR was 14% (11–16%). The median PEEP at baseline was 12 (10–15) cmH 2 O and the PEEP-test resulted in a median decrease in PEEP of 7 (5–10) cmH 2 O, without difference between volume responsive and unresponsive patients. Among volume responsive patients, the PEEP-test induced a significant increase in CI of 16% (12–20%) (from 2.4 ± 0.7 to 2.9 ± 0.9 L/min/m 2 , p  < 0.0001) in comparison with volume unresponsive patients. In volume unresponsive patients, PLR and the PEEP-test increased CI by 2% (1–5%) and 6% (3–8%), respectively. Volume responsiveness was predicted by an increase in CI > 8.6% during the PEEP-test with a sensitivity of 96.8% (95% confidence interval (95%CI): 83.3–99.9%) and a specificity of 84.9% (95%CI 68.1–94.9%). The area under the receiver operating characteristic curve of the PEEP-test for detecting volume responsiveness was 0.94 (95%CI 0.85–0.98) ( p  < 0.0001 vs. 0.5). Spearman’s correlation coefficient between the changes in CI induced by PLR and the PEEP-test was 0.76 (95%CI 0.63–0.85, p  < 0.0001). Conclusions A CI increase > 8.6% during a PEEP-test, which consists in reducing PEEP to 5 cmH 2 O, reliably detects volume responsiveness in mechanically ventilated patients with a PEEP ≥ 10 cmH 2 O. Trial registration ClinicalTrial.gov (NCT 04,023,786). Registered July 18, 2019. Ethics Committee approval CPP Est III (N° 2018-A01599-46).

Background Extracorporeal membrane oxygenation (ECMO) was frequently used to treat patients with severe coronavirus disease-2019 (COVID-19)-associated acute respiratory distress (ARDS) during the initial outbreak. Care of COVID-19 patients evolved markedly during the second part of 2020. Our objective was to compare the characteristics and outcomes of patients who received ECMO for severe COVID-19 ARDS before or after July 1, 2020. Methods We included consecutive adults diagnosed with COVID-19 in Paris–Sorbonne University Hospital Network ICUs, who received ECMO for severe ARDS until January 28, 2021. Characteristics and survival probabilities over time were estimated during the first and second waves. Pre-ECMO risk factors predicting 90-day mortality were assessed using multivariate Cox regression. Results Characteristics of the 88 and 71 patients admitted, respectively, before and after July 1, 2020, were comparable except for older age, more frequent use of dexamethasone (18% vs. 82%), high-flow nasal oxygenation (19% vs. 82%) and/or non-invasive ventilation (7% vs. 37%) after July 1. Respective estimated probabilities (95% confidence intervals) of 90-day mortality were 36% (27–47%) and 48% (37–60%) during the first and the second periods. After adjusting for confounders, probability of 90-day mortality was significantly higher for patients treated after July 1 (HR 2.27, 95% CI 1.02–5.07). ECMO-related complications did not differ between study periods. Conclusions 90-day mortality of ECMO-supported COVID-19–ARDS patients increased significantly after July 1, 2020, and was no longer comparable to that of non-COVID ECMO-treated patients. Failure of prolonged non-invasive oxygenation strategies before intubation and increased lung damage may partly explain this outcome.

PurposeCoronavirus disease 2019 (COVID-19) is creating an unprecedented healthcare crisis. Understanding the determinants of mortality is crucial to optimise intensive care unit (ICU) resource use and to identify targets for improving survival.MethodsIn a multicentre retrospective study, we included 379 COVID-19 patients admitted to four ICUs between 20 February and 24 April 2020 and categorised according to time from disease onset to ICU admission. A Cox proportional-hazards model identified factors associated with 28-day mortality.ResultsMedian age was 66 years (53–68) and 292 (77%) were men. The main comorbidities included obesity and overweight (67%), hypertension (49.6%) and diabetes (30.1%). Median time from disease onset (i.e., viral symptoms) to ICU admission was 8 (6–11) days (missing for three); 161 (42.5%) patients were admitted within a week of disease onset, 173 (45.6%) between 8 and 14 days, and 42 (11.1%) > 14 days after disease onset; day 28 mortality was 26.4% (22–31) and decreased as time from disease onset to ICU admission increased, from 37 to 21% and 12%, respectively. Patients admitted within the first week had higher SOFA scores, more often had thrombocytopenia or acute kidney injury, had more limited radiographic involvement, and had significantly higher blood IL-6 levels. Age, COPD, immunocompromised status, time from disease onset, troponin concentration, and acute kidney injury were independently associated with mortality.ConclusionThe excess mortality in patients admitted within a week of disease onset reflected greater non-respiratory severity. Therapeutic interventions against SARS-CoV-2 might impact different clinical endpoints according to time since disease onset.