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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.

Monitoring inspiratory drive and effort may aid proper selection and setting of respiratory support in patients with acute respiratory failure (ARF), whether they are intubated or not. Although diaphragmatic electrical activity (EAdi) and esophageal manometry can be considered the reference methods for assessing respiratory drive and inspiratory effort, respectively, various alternative techniques exist, each with distinct advantages and limitations. This narrative review provides a comprehensive overview of bedside methods to assess respiratory drive and effort, with a primary focus on patients with ARF. First, EAdi and esophageal manometry are described and discussed as reference techniques. Then, alternative methods are categorized along the neuromechanical pathway from inspiratory drive to muscular effort into three groups: (1) techniques assessing the respiratory drive: airway occlusion pressure (P0.1), mean inspiratory flow (Vt/Ti) and respiratory muscle surface electromyography (sEMG); (2) techniques assessing the respiratory muscle effort: whole-breath occlusion pressure (ΔPocc), pressure-muscle index (PMI), nasal pressure swing (ΔPnose), diaphragm ultrasonography (USdi), central venous pressure swing (ΔCVP), breathing effort (BREF) models, and flow index; (3) techniques and clinical parameters assessing the consequences of effort: tidal volume (Vt), electrical impedance tomography (EIT), dyspnea. For each, we summarize the physiological rationale, measurement methodology, interpretation of results, and key limitations.

This article is one of ten reviews selected from the Annual Update in Intensive Care and Emergency Medicine 2020. Other selected articles can be found online at https://www.biomedcentral.com/collections/annualupdate2020 . Further information about the Annual Update in Intensive Care and Emergency Medicine is available from http://www.springer.com/series/8901 .

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 cmH 2 O/μV with a RC of 82.6%. This implies that when NMEoccl is 1.22 cmH 2 O/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.

Background For every day a person is dependent on mechanical ventilation, respiratory and cardiac complications increase, quality of life decreases and costs increase by > $USD 1500. Interventions that improve respiratory muscle function during mechanical ventilation can reduce ventilation duration. The aim of this pilot study was to assess the feasibility of employing an abdominal functional electrical stimulation (abdominal FES) training program with critically ill mechanically ventilated patients. We also investigated the effect of abdominal FES on respiratory muscle atrophy, mechanical ventilation duration and intensive care unit (ICU) length of stay. Methods Twenty critically ill mechanically ventilated participants were recruited over a 6-month period from one metropolitan teaching hospital. They were randomly assigned to receive active or sham (control) abdominal FES for 30 min, twice per day, 5 days per week, until ICU discharge. Feasibility was assessed through participant compliance to stimulation sessions. Abdominal and diaphragm muscle thickness were measured using ultrasound 3 times in the first week, and weekly thereafter by a blinded assessor. Respiratory function was recorded when the participant could first breathe independently and at ICU discharge, with ventilation duration and ICU length of stay also recorded at ICU discharge by a blinded assessor. Results Fourteen of 20 participants survived to ICU discharge (8, intervention; 6, control). One control was transferred before extubation, while one withdrew consent and one was withdrawn for staff safety after extubation. Median compliance to stimulation sessions was 92.1% (IQR 5.77%) in the intervention group, and 97.2% (IQR 7.40%) in the control group ( p  = 0.384). While this pilot study is not adequately powered to make an accurate statistical conclusion, there appeared to be no between-group thickness changes of the rectus abdominis ( p  = 0.099 at day 3), diaphragm ( p  = 0.652 at day 3) or combined lateral abdominal muscles ( p  = 0.074 at day 3). However, ICU length of stay ( p  = 0.011) and ventilation duration ( p  = 0.039) appeared to be shorter in the intervention compared to the control group. Conclusions Our compliance rates demonstrate the feasibility of using abdominal FES with critically ill mechanically ventilated patients. While abdominal FES did not lead to differences in abdominal muscle or diaphragm thickness, it may be an effective method to reduce ventilation duration and ICU length of stay in this patient group. A fully powered study into this effect is warranted. Trial registration The Australian New Zealand Clinical Trials Registry, ACTRN12617001180303 . Registered 9 August 2017.

Background Prolonged weaning from mechanical ventilation is associated with poor clinical outcome. Therefore, choosing the right moment for weaning and extubation is essential. Electrical Impedance Tomography (EIT) is a promising innovative lung monitoring technique, but its role in supporting weaning decisions is yet uncertain. We aimed to evaluate physiological trends during a T-piece spontaneous breathing trail (SBT) as measured with EIT and the relation between EIT parameters and SBT success or failure. Methods This is an observational study in which twenty-four adult patients receiving mechanical ventilation performed an SBT. EIT monitoring was performed around the SBT. Multiple EIT parameters including the end-expiratory lung impedance (EELI), delta Tidal Impedance (ΔZ), Global Inhomogeneity index (GI), Rapid Shallow Breathing Index (RSBI EIT ), Respiratory Rate (RR EIT ) and Minute Ventilation (MV EIT ) were computed on a breath-by-breath basis from stable tidal breathing periods. Results EELI values dropped after the start of the SBT ( p  < 0.001) and did not recover to baseline after restarting mechanical ventilation. The ΔZ dropped ( p  < 0.001) but restored to baseline within seconds after restarting mechanical ventilation. Five patients failed the SBT, the GI ( p  = 0.01) and transcutaneous CO 2 ( p  < 0.001) values significantly increased during the SBT in patients who failed the SBT compared to patients with a successful SBT. Conclusion EIT has the potential to assess changes in ventilation distribution and quantify the inhomogeneity of the lungs during the SBT. High lung inhomogeneity was found during SBT failure. Insight into physiological trends for the individual patient can be obtained with EIT during weaning from mechanical ventilation, but its role in predicting weaning failure requires further study.

This article is one of ten reviews selected from the Annual Update in Intensive Care and Emergency medicine 2017. Other selected articles can be found online at http://ccforum.com/series/annualupdate2017 . Further information about the Annual Update in Intensive Care and Emergency Medicine is available from http://www.springer.com/series/8901 .

Background Several approaches for setting PEEP in patients with (COVID-19-related) ARDS have been proposed. It is unclear whether a best approach exist, and how the recommended PEEP and resulting transpulmonary pressure, overdistension and collapse relate. Objectives To compare approaches based on electrical impedance tomography (EIT) (including targeting the crossing point of overdistension/collapse curves, EIT CP ) with targeting positive end-expiratory transpulmonary pressure (P L,EE ) and targeting highest respiratory system compliance (C RS ). Methods Post-hoc analysis of 29 patients with COVID-19-related ARDS from cohorts of two Dutch hospitals. Patients underwent a decremental PEEP trial, while EIT data and esophageal pressure data were recorded. We compared the recommended PEEP, as well as resulting P L,EE and amounts of overdistension and collapse at the suggested PEEP. Results Targeting EIT CP resulted in higher recommended PEEP (14 [12–16] cmH 2 O) compared to a positive P L,EE (12 [8–14] cmH 2 O), while highest C RS resulted in intermediate PEEP levels. Individually, the difference between the highest and lowest recommended PEEP level were 6 [4–8] cmH 2 O. P L,EE at the recommended PEEP was generally higher when targeting EIT CP compared to and positive P L,EE (1.4 [0.6–2.1] cmH 2 O). The amount of collapse was lowest with EIT CP (3.0 [2.0–4.0]%) and highest when targeting P L,EE (5.4 [2.0–12.0]%). No significant differences in the amount of overdistension were found. Targeting positive P L,EE resulted in 51% patients with high (> 10%) values for either overdistension or collapse, more than any other method. Conclusions Targeting EIT CP results in slightly higher recommended PEEP and P L,EE levels compared to positive P L,EE , leading to less collapse, but not more overdistension. EIT-based methods protect better against high values of either overdistension or collapse.