Effect of prone position on regional shunt, aeration, and perfusion in experimental acute lung injury

Extended Prone Position and 90-Day Mortality in Mechanically Ventilated Patients With COVID-19

BACKGROUND

Prone positioning (PP) has demonstrated its potential for improving outcomes in patients with ARDS who require invasive mechanical ventilation. However, the ability of prolonged proning to reduce mortality in patients with COVID-19 specifically, sessions lasting > 24 h remains uncertain.

METHODS

In this retrospective cohort study, we examined 158 subjects with COVID-19 pneumonia who required mechanical ventilation due to moderate-to-severe ARDS. Seventy-six subjects were placed in standard PP and 82 in extended PP, defined as prone sessions lasting at least 32 h. Our primary aim was to evaluate the effect of EPP on 90-d survival in subjects with COVID-19 with acute severe respiratory failure. To ensure the reliability of our findings and to minimize bias, we applied 3 adjustment approaches: cardinality matching (CM), matching weighting (MW), and inverse probability of treatment weighting with stabilized and trimmed weights (SW). We used Kaplan-Meier curves and Cox proportional hazard models to analyze the effects of EPP on 90-d mortality and sensitivity analysis by calculating E-values.

RESULTS

The overall crude 90-d mortality rate was 31.7%. The unadjusted 90-d mortality rates were 19.5% in the EPP group and 44.7% in the SPP group (hazard ratio [HR] 0.35 [95% CI 0.19- 0.63], P < .001). After adjustment for confounding factors using CM, MW, and SW, baseline covariates were balanced between the 2 groups. Subjects in the EPP group exhibited lower 90-d mortality rates after adjustment using CM (HR 0.42 [95% CI 0.23-0.79], P = .007), MW (HR 0.45 [95% CI 0.21-0.95], P = .036), or SW (HR 0.29 [95% CI 0.15-0.56], P < .001).

CONCLUSIONS

Extended PP was associated with improved 90-d survival in subjects with COVID-19 undergoing mechanical ventilation for severe ARDS. These findings suggest the potential benefit of EPP in the management of COVID-19-related respiratory failure. Further research and prospective studies are warranted to confirm and elucidate the underlying mechanisms of this association.

Respiratory effects of prone position in COVID-19 acute respiratory distress syndrome differ according to the recruitment-to-inflation ratio: a prospective observational study

BACKGROUND

Improvements in oxygenation and lung mechanics with prone position (PP) in patients with acute respiratory distress syndrome (ARDS) are inconstant. The objectives of the study were (i) to identify baseline variables, including the recruitment-to-inflation ratio (R/I), associated with a positive response to PP in terms of oxygenation (improvement of the ratio of arterial oxygen partial pressure over the inspired oxygen fraction (PaO2/FiO2) ≥ 20 mmHg) and lung mechanics; (ii) to evaluate whether the response to the previous PP session is associated with the response to the next session.

METHODS

In this prospective, observational, single-center study in patients who underwent PP for ARDS due to COVID-19, respiratory variables were assessed just before PP and at the end of the session. Respiratory variables included mechanical ventilation settings and respiratory mechanics variables, including R/I, an estimate of the potential for lung recruitment compared to lung overinflation.

RESULTS

In 50 patients, 201 PP sessions lasting 19 ± 3 h were evaluated. Neuromuscular blockades were used in 116 (58%) sessions. The PaO2/FiO2 ratio increased from 109 ± 31 mmHg to 165 ± 65 mmHg, with an increase ≥ 20 mmHg in 142 (71%) sessions. In a mixed effect logistic regression, only pre-PP PaO2/FiO2 (OR 1.12 (95% CI [1.01-1.24])/every decrease of 10 mmHg, p = 0.034) in a first model and improvement in oxygenation at the previous PP session (OR 3.69 (95% CI [1.27-10.72]), p = 0.017) in a second model were associated with an improvement in oxygenation with PP. The R/I ratio (n = 156 sessions) was 0.53 (0.30-0.76), separating lower- and higher-recruiters. Whereas PaO2/FiO2 improved to the same level in both subgroups, driving pressure and respiratory system compliance improved only in higher-recruiters (from 14 ± 4 to 12 ± 4 cmH2O, p = 0.027, and from 34 ± 11 to 38 ± 13 mL/cmH2O, respectively, p = 0.014).

CONCLUSIONS

A lower PaO2/FiO2 at baseline and a positive O2-response at the previous PP session are associated with a PP-induced improvement in oxygenation. In higher-recruiters, lung mechanics improved along with oxygenation. Benefits of PP could thus be greater in these patients.

Positive end-expiratory pressure management in patients with severe ARDS: implications of prone positioning and extracorporeal membrane oxygenation

The optimal strategy for positive end-expiratory pressure (PEEP) titration in the management of severe acute respiratory distress syndrome (ARDS) patients remains unclear. Current guidelines emphasize the importance of a careful risk-benefit assessment for PEEP titration in terms of cardiopulmonary function in these patients. Over the last few decades, the primary goal of PEEP usage has shifted from merely improving oxygenation to emphasizing lung protection, with a growing focus on the individual pattern of lung injury, lung and chest wall mechanics, and the hemodynamic consequences of PEEP. In moderate-to-severe ARDS patients, prone positioning (PP) is recommended as part of a lung protective ventilation strategy to reduce mortality. However, the physiologic changes in respiratory mechanics and hemodynamics during PP may require careful re-assessment of the ventilation strategy, including PEEP. For the most severe ARDS patients with refractory gas exchange impairment, where lung protective ventilation is not possible, veno-venous extracorporeal membrane oxygenation (V-V ECMO) facilitates gas exchange and allows for a "lung rest" strategy using "ultraprotective" ventilation. Consequently, the importance of lung recruitment to improve oxygenation and homogenize ventilation with adequate PEEP may differ in severe ARDS patients treated with V-V ECMO compared to those managed conservatively. This review discusses PEEP management in severe ARDS patients and the implications of management with PP or V-V ECMO with respect to respiratory mechanics and hemodynamic function.

Early reapplication of prone position during venovenous ECMO for acute respiratory distress syndrome: a prospective observational study and propensity-matched analysis

BACKGROUND

A combination of prone positioning (PP) and venovenous extracorporeal membrane oxygenation (VV-ECMO) is safe, feasible, and associated with potentially improved survival for severe acute respiratory distress syndrome (ARDS). However, whether ARDS patients, especially non-COVID-19 patients, placed in PP before VV-ECMO should continue PP after a VV-ECMO connection is unknown. This study aimed to test the hypothesis that early use of PP during VV-ECMO could increase the proportion of patients successfully weaned from ECMO support in severe ARDS patients who received PP before ECMO.

METHODS

In this prospective observational study, patients with severe ARDS who were treated with VV-ECMO were divided into two groups: the prone group and the supine group, based on whether early PP was combined with VV-ECMO. The proportion of patients successfully weaned from VV-ECMO and 60-day mortality were analyzed before and after propensity score matching.

RESULTS

A total of 165 patients were enrolled, 50 in the prone and 115 in the supine group. Thirty-two (64%) and 61 (53%) patients were successfully weaned from ECMO in the prone and the supine groups, respectively. The proportion of patients successfully weaned from VV-ECMO in the prone group tended to be higher, albeit not statistically significant. During PP, there was a significant increase in partial pressure of arterial oxygen (PaO2) without a change in ventilator or ECMO settings. Tidal impedance shifted significantly to the dorsal region, and lung ultrasound scores significantly decreased in the anterior and posterior regions. Forty-five propensity score-matched patients were included in each group. In this matched sample, the prone group had a higher proportion of patients successfully weaned from VV-ECMO (64.4% vs. 42.2%; P = 0.035) and lower 60-day mortality (37.8% vs. 60.0%; P = 0.035).

CONCLUSIONS

Patients with severe ARDS placed in PP before VV-ECMO should continue PP after VV-ECMO support. This approach could increase the probability of successful weaning from VV-ECMO.

TRIAL REGISTRATION

ClinicalTrials.Gov: NCT04139733. Registered 23 October 2019.

Mechanical ventilation guided by driving pressure optimizes local pulmonary biomechanics in an ovine model

Mechanical ventilation exposes the lung to injurious stresses and strains that can negatively affect clinical outcomes in acute respiratory distress syndrome or cause pulmonary complications after general anesthesia. Excess global lung strain, estimated as increased respiratory system driving pressure, is associated with mortality related to mechanical ventilation. The role of small-dimension biomechanical factors underlying this association and their spatial heterogeneity within the lung are currently unknown. Using four-dimensional computed tomography with a voxel resolution of 2.4 cubic millimeters and a multiresolution convolutional neural network for whole-lung image segmentation, we dynamically measured voxel-wise lung inflation and tidal parenchymal strains. Healthy or injured ovine lungs were evaluated as the mechanical ventilation positive end-expiratory pressure (PEEP) was titrated from 20 to 2 centimeters of water. The PEEP of minimal driving pressure (PEEPDP) optimized local lung biomechanics. We observed a greater rate of change in nonaerated lung mass with respect to PEEP below PEEPDP compared with PEEP values above this threshold. PEEPDP similarly characterized a breaking point in the relationships between PEEP and SD of local tidal parenchymal strain, the 95th percentile of local strains, and the magnitude of tidal overdistension. These findings advance the understanding of lung collapse, tidal overdistension, and strain heterogeneity as local triggers of ventilator-induced lung injury in large-animal lungs similar to those of humans and could inform the clinical management of mechanical ventilation to improve local lung biomechanics.

Deep learning segmentation and registration-driven lung parenchymal volume and movement CT analysis in prone positioning

PURPOSE

To conduct a volumetric and movement analysis of lung parenchyma in prone positioning using deep neural networks (DNNs).

METHOD

We included patients with suspected interstitial lung abnormalities or disease who underwent full-inspiratory supine and prone chest CT at a single institution between June 2021 and March 2022. A thoracic radiologist visually assessed the fibrosis extent in the total lung (using units of 10%) on supine CT. After preprocessing the images into 192×192×192 resolution, a DNN automatically segmented the whole lung and pulmonary lobes in prone and supine CT images. Affine registration matched the patient's center and location, and the DNN deformably registered prone and supine CT images to calculate the x-, y-, z-axis, and 3D pixel movements.

RESULTS

In total, 108 CT pairs had successful registration. Prone positioning significantly increased the left lower (90.2±69.5 mL, P = 0.000) and right lower lobar volumes (52.5±74.2 mL, P = 0.000). During deformable registration, the average maximum whole-lung pixel movements between the two positions were 1.5, 1.9, 1.6, and 2.8 cm in each axis and 3D plane. Compared to patients with <30% fibrosis, those with ≥30% fibrosis had smaller volume changes (P<0.001) and smaller pixel movements in all axes between the positions (P = 0.000-0.007). Forced vital capacity (FVC) correlated with the left lower lobar volume increase (Spearman correlation coefficient, 0.238) and the maximum whole-lung pixel movements in all axes (coefficients, 0.311 to 0.357).

CONCLUSIONS

Prone positioning led to the preferential expansion of the lower lobes, correlated with FVC, and lung fibrosis limited lung expansion during prone positioning.

Prone positioning during CPAP therapy in SARS-CoV-2 pneumonia: a concise clinical review

During the COVID-19 pandemic, the number of patients with hypoxemic acute respiratory failure (ARF) due to SARS-CoV-2 pneumonia threatened to overwhelm intensive care units. To reduce the need for invasive mechanical ventilation (IMV), clinicians tried noninvasive strategies to manage ARF, including the use of awake prone positioning (PP) with continuous positive airway pressure (CPAP). In this article, we review the patho-physiologic rationale, clinical effectiveness and practical issues of the use of PP during CPAP in non-intubated, spontaneously breathing patients affected by SARS-CoV-2 pneumonia with ARF. Use of PP during CPAP appears to be safe and feasible and may have a lower rate of adverse events compared to IMV. A better response to PP is observed among patients in early phases of acute respiratory distress syndrome. While PP during CPAP may improve oxygenation, the impact on the need for intubation and mortality remains unclear. It is possible to speculate on the role of PP during CPAP in terms of improvement of ventilation mechanics and reduction of strain stress.

Improved oxygenation in prone positioning of mechanically ventilated patients with COVID-19 acute respiratory distress syndrome is associated with decreased pulmonary shunt fraction: a prospective multicenter study

BACKGROUND

Prone position is used in acute respiratory distress syndrome and in coronavirus disease 2019 (Covid-19) acute respiratory distress syndrome (ARDS). However, physiological mechanisms remain unclear. The aim of this study was to determine whether improved oxygenation was related to pulmonary shunt fraction (Q's/Q't), alveolar dead space (Vd/Vtalv) and ventilation/perfusion mismatch (V'A/Q').

METHODS

This was an international, prospective, observational, multicenter, cohort study, including six intensive care units in Sweden and Poland and 71 mechanically ventilated adult patients.

RESULTS

Prone position increased PaO2:FiO2 after 30 min, by 78% (83-148 mm Hg). The effect persisted 120 min after return to supine (p < 0.001). The oxygenation index decreased 30 min after prone positioning by 43% (21-12 units). Q's/Q't decreased already after 30 min in the prone position by 17% (0.41-0.34). The effect persisted 120 min after return to supine (p < 0.005). Q's/Q't and PaO2:FiO2 were correlated both in prone (Beta -137) (p < 0.001) and in the supine position (Beta -270) (p < 0.001). V'A/Q' was unaffected and did not correlate to PaO2:FiO2 (p = 0.8). Vd/Vtalv increased at 120 min by 11% (0.55-0.61) (p < 0.05) and did not correlate to PaO2:FiO2 (p = 0.3). The ventilatory ratio increased after 30 min in the prone position by 58% (1.9-3.0) (p < 0.001). PaO2:FiO2 at baseline predicted PaO2:FiO2 at 30 min after proning (Beta 1.3) (p < 0.001).

CONCLUSIONS

Improved oxygenation by prone positioning in COVID-19 ARDS patients was primarily associated with a decrease in pulmonary shunt fraction. Dead space remained high and the global V'A/Q' measure could not explain the differences in gas exchange.

Prone Positioning for Patients With COVID-19-Induced Acute Hypoxemic Respiratory Failure: Flipping the Script

During the COVID-19 pandemic, prone positioning (PP) emerged as a widely used supportive therapy for patients with acute hypoxemic respiratory failure caused by COVID-19 infection. In particular, awake PP (APP)-the placement of non-intubated patients in the prone position-has gained popularity and hence is detailed first herein. This review discusses recent publications on the use of PP for non-intubated and intubated subjects with COVID-19, highlighting the physiological responses, clinical outcomes, influential factors affecting treatment success, and strategies to improve adherence with APP. The use of prolonged PP and the use of PP for patients undergoing extracorporeal membrane oxygenation are also presented.

Hemodynamic Implications of Prone Positioning in Patients with ARDS

This article is one of ten reviews selected from the Annual Update in Intensive Care and Emergency Medicine 2023. Other selected articles can be found online at https://www.biomedcentral.com/collections/annualupdate2023 . Further information about the Annual Update in Intensive Care and Emergency Medicine is available from https://link.springer.com/bookseries/8901 .

Prone position decreases acute lung inflammation measured by [11C](R)-PK11195 positron emission tomography in experimental acute respiratory distress syndrome

Whether prone positioning (PP) modulates acute lung inflammation by the modulation of biomechanical forces of ventilator-induced lung injuries (VILIs) remains unclear. We aimed to demonstrate that PP decreases acute lung inflammation in animals with experimental acute respiratory distress syndrome (ARDS). Animals were under general anesthesia and protective ventilation (tidal volume 6 mL·kg^-1, PEEP 5 cmH₂O). ARDS was induced by intratracheal instillation of chlorohydric acid. Animals were then randomized to PP, or to supine position (SP). After 4 h, a positron emission tomography (PET) acquisition with [¹¹C](R)-PK11195 was performed coupled with computerized tomography (CT) acquisitions, allowing the CT quantification of VILI-associated parameters. [¹¹C](R)-PK11195 lung uptake was quantified using pharmacokinetic multicompartment models. Analyses were performed on eight lung sections distributed along the antero-posterior dimension. Six animals were randomized to PP, five to SP (median [Formula: see text]/[Formula: see text] [interquartile range]: 164 [102-269] mmHg). The normally aerated compartment was significantly redistributed to the posterior lung regions of animals in PP, compared with SP. Dynamic strain was significantly increased in posterior regions of SP animals, compared with PP. After 4 h, animals in PP had a significantly lower uptake of [¹¹C](R)-PK11195, compared with SP. [¹¹C](R)-PK11195 regional uptake was independently associated with the study group, dynamic strain, tidal hyperinflation, and regional respiratory system compliance in multivariate analysis. In an experimental model of ARDS, 4 h of PP significantly decreased acute lung inflammation assessed with PET. The beneficial impact of PP on acute lung inflammation was consecutive to the combination of decreased biomechanical forces and changes in the respiratory system mechanics.NEW & NOTEWORTHY Prone position decreases acute lung macrophage inflammation quantified in vivo with [¹¹C](R)-PK11195 positron emission tomography in an experimental acute respiratory distress syndrome. Regional macrophage inflammation is maximal in the most anterior and posterior lung section of supine animals, in relation with increased regional tidal strain and hyperinflation, and reduced regional lung compliance.

Understanding clinical and biological heterogeneity to advance precision medicine in paediatric acute respiratory distress syndrome

Paediatric acute respiratory distress syndrome (PARDS) is a heterogeneous clinical syndrome that is associated with high rates of mortality and long-term morbidity. Factors that distinguish PARDS from adult acute respiratory distress syndrome (ARDS) include changes in developmental stage and lung maturation with age, precipitating factors, and comorbidities. No specific treatment is available for PARDS and management is largely supportive, but methods to identify patients who would benefit from specific ventilation strategies or ancillary treatments, such as prone positioning, are needed. Understanding of the clinical and biological heterogeneity of PARDS, and of differences in clinical features and clinical course, pathobiology, response to treatment, and outcomes between PARDS and adult ARDS, will be key to the development of novel preventive and therapeutic strategies and a precision medicine approach to care. Studies in which clinical, biomarker, and transcriptomic data, as well as informatics, are used to unpack the biological and phenotypic heterogeneity of PARDS, and implementation of methods to better identify patients with PARDS, including methods to rapidly identify subphenotypes and endotypes at the point of care, will drive progress on the path to precision medicine.

Hemodynamic and Respiratory Changes following Prone Position in Acute Respiratory Distress Syndrome Patients: A Clinical Study

BACKGROUND

Limited data are available for the oxygenation changes following prone position in relation to hemodynamic and pulmonary vascular variations in acute respiratory distress syndrome (ARDS), using reliable invasive methods. We aimed to assess oxygenation and hemodynamic changes between the supine and prone posture in patients with ARDS and identify parameters associated with oxygenation improvement.

METHODS

Eighteen patients with ARDS under protective ventilation were assessed using advanced pulmonary artery catheter monitoring. Physiologic parameters were recorded at baseline supine position, 1 h and 18 h following prone position.

RESULTS

The change in the Oxygenation Index (ΔOI) between supine and 18 h prone significantly correlated to the concurrent change in shunt fraction (r = 0.75, p = 0.0001), to the ΔOI between supine and 1 h prone (r = 0.73, p = 0.001), to the supine acute lung injury score and the OI (r = -0.73, p = 0.009 and r = 0.69, p = 0.002, respectively). Cardiac output did not change between supine and prone posture. Moreover, there was no change in pulmonary pressure, pulmonary vascular resistances, right ventricular (RV) volumes and the RV ejection fraction.

CONCLUSIONS

The present investigation provides physiologic clinical data supporting that oxygenation improvement following prone position in ARDS is driven by the shunt fraction reduction and not by changes in hemodynamics. Moreover, oxygenation improvement was not correlated with RV or pulmonary circulation changes.

Prone position: how understanding and clinical application of a technique progress with time

Historical background

The prone position was first proposed on theoretical background in 1974 (more advantageous distribution of mechanical ventilation). The first clinical report on 5 ARDS patients in 1976 showed remarkable improvement of oxygenation after pronation. 

Pathophysiology

The findings in CT scans enhanced the use of prone position in ARDS patients. The main mechanism of the improved gas exchange seen in the prone position is nowadays attributed to a dorsal ventilatory recruitment, with a substantially unchanged distribution of perfusion. Regardless of the gas exchange, the primary effect of the prone position is a more homogenous distribution of ventilation, stress and strain, with similar size of pulmonary units in dorsal and ventral regions. In contrast, in the supine position the ventral regions are more expanded compared with the dorsal regions, which leads to greater ventral stress and strain, induced by mechanical ventilation.

Outcome in ARDS

The number of clinical studies paralleled the evolution of the pathophysiological understanding. The first two clinical trials in 2001 and 2004 were based on the hypothesis that better oxygenation would lead to a better survival and the studies were more focused on gas exchange than on lung mechanics. The equations better oxygenation = better survival was disproved by these and other larger trials (ARMA trial). However, the first studies provided signals that some survival advantages were possible in a more severe ARDS, where both oxygenation and lung mechanics were impaired. The PROSEVA trial finally showed the benefits of prone position on mortality supporting the thesis that the clinical advantages of prone position, instead of improved gas exchange, were mainly due to a less harmful mechanical ventilation and better distribution of stress and strain. In less severe ARDS, in spite of a better gas exchange, reduced mechanical stress and strain, and improved oxygenation, prone position was ineffective on outcome.

Prone position and COVID-19

The mechanisms of oxygenation impairment in early COVID-19 are different than in typical ARDS and relate more on perfusion alteration than on alveolar consolidation/collapse, which are minimal in the early phase. Bronchial shunt may also contribute to the early COVID-19 hypoxemia. Therefore, in this phase, the oxygenation improvement in prone position is due to a better matching of local ventilation and perfusion, primarily caused by the perfusion component. Unfortunately, the conditions for improved outcomes, i.e. a better distribution of stress and strain, are almost absent in this phase of COVID-19 disease, as the lung parenchyma is nearly fully inflated. Due to some contradictory results, further studies are needed to better investigate the effect of prone position on outcome in COVID-19 patients.

Graphical Abstract

Effects of awake prone position vs. usual care on acute hypoxemic respiratory failure in patients with COVID-19: A systematic review and meta-analysis of randomized controlled trials

Background

Previous studies have shown that an awake prone position may be beneficial for the treatment of acute respiratory distress syndrome (ARDS) or acute hypoxic respiratory failure (AHRF) in patients with COVID-19, but the results are not consistent, especially in terms of oxygenation outcomes and intubation rate. This systematic review and meta-analysis assessed the effects of the awake prone position on AHRF in patients with COVID-19 with all randomized controlled trials (RCTs).

Methods

An extensive search of online databases, including MEDLINE, Embase, Web of Science, and Cochrane Central Register of Controlled Trials from 1 December 2019 to 30 October 2022, with no language restrictions was performed. This systematic review and meta-analysis are based on the PRISMA statement. We only included RCTs and used the Cochrane risk assessment tool for quality assessment.

Results

Fourteen RCTs fulfilled the selection criteria, and 3,290 patients were included. A meta-analysis found that patients in the awake prone position group had more significant improvement in the SpO₂/FiO₂ ratio [mean difference (MD): 29.76; 95% confidence interval (CI): 1.39-48.13; P = 0.001] compared with the usual care. The prone position also reduced the need for intubation [odd ratio (OR): 0.72; 95% CI: 0.61 to 0.84; P < 0.0001; I ² = 0%]. There was no significant difference in mortality, hospital length of stay, incidence of intensive care unit (ICU) admission, and adverse events between the two groups.

Conclusion

The awake prone position was a promising intervention method, which is beneficial to improve the oxygenation of patients with ARDS or AHRF caused by COVID-19 and reduce the need for intubation. However, the awake prone position showed no obvious advantage in mortality, hospital length of stay, incidence of ICU admission, and adverse events.

Systematic review registration

International Prospective Register of Systematic Reviews (PROSPERO), identifier: CRD42022367885.

Early decrease of ventilatory ratio after prone position ventilation may predict successful weaning in patients with acute respiratory distress syndrome: A retrospective cohort study

Background

Previous studies usually identified patients who benefit the most from prone positioning by oxygenation improvement. However, inconsistent results have been reported. Physiologically, pulmonary dead space fraction may be more appropriate in evaluating the prone response. As an easily calculated bedside index, ventilatory ratio (VR) correlates well with pulmonary dead space fraction. Hence, we investigated whether the change in VR after prone positioning is associated with weaning outcomes at day 28 and to identify patients who will benefit the most from prone positioning.

Materials and methods

This retrospective cohort study was performed in a group of mechanically ventilated, non-COVID ARDS patients who received prone positioning in the ICU at Zhongda hospital, Southeast University. The primary outcome was the rate of successful weaning patients at day 28. Arterial blood gas results and corresponding ventilatory parameters on five different time points around the first prone positioning were collected, retrospectively. VR responders were identified by Youden's index. Competing-risk regression models were used to identify the association between the VR change and liberation from mechanical ventilation at day 28.

Results

One hundred and three ARDS patients receiving prone positioning were included, of whom 53 (51%) successfully weaned from the ventilator at day 28. VR responders were defined as patients showing a decrease in VR of greater than or equal to 0.037 from the baseline to within 4 h after prone. VR responders have significant longer ventilator-free days, higher successful weaning rates and lower mortality compared with non-responders at day 28. And a significant between-group difference exists in the respiratory mechanics improvement after prone (P < 0.05). A linear relationship was also found between VR change and compliance of the respiratory system (Crs) change after prone (r = 0.32, P = 0.025). In the multivariable competing-risk analysis, VR change (sHR 0.57; 95% CI, 0.35-0.92) was independently associated with liberation from mechanical ventilation at day 28.

Conclusion

Ventilatory ratio decreased more significantly within 4 h after prone positioning in patients with successful weaning at day 28. VR change was independently associated with liberation from mechanical ventilation at day 28.

Effect of prone positioning on end-expiratory lung volume, strain and oxygenation change over time in COVID-19 acute respiratory distress syndrome: A prospective physiological study

Background

Prone position (PP) is a recommended intervention in severe classical acute respiratory distress syndrome (ARDS). Changes in lung resting volume, respiratory mechanics and gas exchange during a 16-h cycle of PP in COVID-19 ARDS has not been yet elucidated.

Methods

Patients with severe COVID-19 ARDS were enrolled between May and September 2021 in a prospective cohort study in a University Teaching Hospital. Lung resting volume was quantitatively assessed by multiple breath nitrogen wash-in/wash-out technique to measure the end-expiratory lung volume (EELV). Timepoints included the following: Baseline, Supine Position (S1); start of PP (P0), and every 4-h (P4; P8; P12) until the end of PP (P16); and Supine Position (S2). Respiratory mechanics and gas exchange were assessed at each timepoint.

Measurements and main results

40 mechanically ventilated patients were included. EELV/predicted body weight (PBW) increased significantly over time. The highest increase was observed at P4. The highest absolute EELV/PBW values were observed at the end of the PP (P16 vs S1; median 33.5 ml/kg [InterQuartileRange, 28.2-38.7] vs 23.4 ml/kg [18.5-26.4], p < 0.001). Strain decreased immediately after PP and remained stable between P4 and P16. PaO2/FiO2 increased during PP reaching the highest level at P12 (P12 vs S1; 163 [138-217] vs 81 [65-97], p < 0.001). EELV/PBW, strain and PaO2/FiO2 decreased at S2 although EELV/PBW and PaO2/FiO2 were still significantly higher as compared to S1. Both absolute values over time and changes of strain and PaO2/FiO2 at P16 and S2 versus S1 were strongly associated with EELV/PBW levels.

Conclusion

In severe COVID-19 ARDS, EELV steadily increased over a 16-h cycle of PP peaking at P16. Strain gradually decreased, and oxygenation improved over time. Changes in strain and oxygenation at the end of PP and back to SP were strongly associated with changes in EELV/PBW. Whether the change in EELV and oxygenation during PP may play a role on outcomes in COVID-ARDS deserves further investigation.

Clinical trial registration

[www.ClinicalTrials.gov], identifier [NCT04818164].

Prone positioning reduces frontal and hippocampal neuronal dysfunction in a murine model of ventilator-induced lung injury

Prone positioning is an established treatment for severe acute lung injury conditions. Neuronal dysfunction frequently occurs with mechanical ventilation-induced acute lung injury (VILI) and clinically manifests as delirium. We previously reported a pathological role for systemic interleukin 6 (IL-6) in mediating neuronal injury. However, currently no studies have investigated the relationship between prone or supine positioning and IL-6 mediated neuronal dysfunction. Here, we hypothesize that prone positioning mitigates neuronal injury, via decreased IL-6, in a model of VILI. VILI was induced by subjecting C57BL/6J mice to high tidal volume (35 cc/kg) mechanical ventilation. Neuronal injury markers [cleaved caspase-3 (CC3), c-fos, heat shock protein 90 (Hsp90)] and inflammatory cytokines (IL-6, IL-1β, TNF-α) were measured in the frontal cortex and hippocampus. We found statistically significantly less neuronal injury (CC3, c-Fos, Hsp90) and inflammatory cytokines (IL-6, IL-1β, TNF-α) in the frontal cortex and hippocampus with prone compared to supine positioning (p < 0.001) despite no significant group differences in oxygen saturation or inflammatory infiltrates in the bronchoalveolar fluid (p > 0.05). Although there were no group differences in plasma IL-6 concentrations, there was significantly less cortical and hippocampal IL-6 in the prone position (p < 0.0001), indicating supine positioning may enhance brain susceptibility to systemic IL-6 during VILI via the IL-6 trans-signaling pathway. These findings call for future clinical studies to assess the relationship between prone positioning and delirium and for investigations into novel diagnostic or therapeutic paradigms to mitigate delirium by reducing expression of systemic and cerebral IL-6.

Effect of prone positioning on gas exchange according to lung morphology in patients with acute respiratory distress syndrome

BACKGROUND

There are limited data on the clinical effects of prone positioning according to lung morphology. We aimed to determine whether the gas exchange response to prone positioning differs according to lung morphology.

METHODS

This retrospective study included adult patients with moderate-to-severe acute respiratory distress syndrome (ARDS). The lung morphology of ARDS was assessed by chest computed tomography scan and classified as "diffuse" or "focal." The primary outcome was change in partial pressure of arterial oxygen to fraction of inspired oxygen (PaO2/FiO2) ratio after the first prone positioning session: first, using the entire cohort, and second, using subgroups of patients with diffuse ARDS matched 2 to 1 with patients with focal ARDS at baseline.

RESULTS

Ninety-five patients were included (focal ARDS group, 23; diffuse ARDS group, 72). Before prone positioning, the focal ARDS group showed worse oxygenation than the diffuse ARDS group (median PaO2/FiO2 ratio, 79.9 mm Hg [interquartile range (IQR)], 67.7-112.6 vs. 104.0 mm Hg [IQR, 77.6-135.7]; P=0.042). During prone positioning, the focal ARDS group showed a greater improvement in the PaO2/FiO2 ratio than the diffuse ARDS group (median, 55.8 mm Hg [IQR, 11.1-109.2] vs. 42.8 mm Hg [IQR, 11.6-83.2]); however, the difference was not significant (P=0.705). Among the PaO2/FiO2-matched cohort, there was no significant difference in change in PaO2/FiO2 ratio after prone positioning between the groups (P=0.904).

CONCLUSIONS

In patients with moderate-to-severe ARDS, changes in PaO2/FiO2 ratio after prone positioning did not differ according to lung morphology. Therefore, prone positioning can be considered as soon as indicated, regardless of ARDS lung morphology.

Imaging the acute respiratory distress syndrome: past, present and future

In patients with the acute respiratory distress syndrome (ARDS), lung imaging is a fundamental tool in the study of the morphological and mechanistic features of the lungs. Chest computed tomography studies led to major advances in the understanding of ARDS physiology. They allowed the in vivo study of the syndrome's lung features in relation with its impact on respiratory physiology and physiology, but also explored the lungs' response to mechanical ventilation, be it alveolar recruitment or ventilator-induced lung injuries. Coupled with positron emission tomography, morphological findings were put in relation with ventilation, perfusion or acute lung inflammation. Lung imaging has always been central in the care of patients with ARDS, with modern point-of-care tools such as electrical impedance tomography or lung ultrasounds guiding clinical reasoning beyond macro-respiratory mechanics. Finally, artificial intelligence and machine learning now assist imaging post-processing software, which allows real-time analysis of quantitative parameters that describe the syndrome's complexity. This narrative review aims to draw a didactic and comprehensive picture of how modern imaging techniques improved our understanding of the syndrome, and have the potential to help the clinician guide ventilatory treatment and refine patient prognostication.

Lung-Dependent Areas Collapse, Monitored by Electrical Impedance Tomography, May Predict the Oxygenation Response to Prone Ventilation in COVID-19 Acute Respiratory Distress Syndrome

OBJECTIVES

ICUs have had to deal with a large number of patients with acute respiratory distress syndrome COVID-19, a significant number of whom received prone ventilation, which is a substantial consumer of care time. The selection of patients that we have to ventilate in prone position seems interesting. We evaluate the correlation between the percentage of collapsed dependent lung areas in the supine position, monitoring by electrical impedance tomography and the oxygenation response (change in Pao2/Fio2 ratio) to prone position.

DESIGN

An observational prospective study.

SETTING

From October 21, 2020, to 30 March 30, 2021. At the Sainte Anne military teaching Hospital and the Timone University Hospital.

PATIENTS

Fifty consecutive patients admitted in our ICUs, with COVID-19 acute respiratory distress syndrome and required mechanical, were included. Twenty-four (48%) received prone ventilation. Fifty-eight prone sessions were investigated.

INTERVENTIONS

An electrical impedance tomography recording was made in supine position, daily and repeated just before and just after the prone session. The daily dependent area collapse was calculated in relation to the previous electrical impedance tomography recording. Prone ventilation response was defined as a Pao2/Fio2 ratio improvement greater than 20%.

MEASUREMENT AND MAIN RESULTS

The main outcome was the correlation between dependent area collapse and the oxygenation response to prone ventilation. Dependent area collapse was correlated with oxygenation response to prone ventilation (R2 = 0.49) and had a satisfactory prediction accuracy of prone response with an area under the curve of 0.94 (95% CI, 0.87-1.00; p < 0.001). Best Youden index was obtained for a dependent area collapse greater than 13.5 %. Sensitivity of 92% (95% CI, 78-97), a specificity of 91% (95% CI, 72-97), a positive predictive value of 94% (95% CI, 88-100), a negative predictive value of 87% (95% CI, 78-96), and a diagnostic accuracy of 91% (95% CI, 84-98).

CONCLUSIONS

Dependent lung areas collapse (> 13.5%), monitored by electrical impedance tomography, has an excellent positive predictive value (94%) of improved oxygenation during prone ventilation.

Prone Positioning and Neuromuscular Blocking Agents as Adjunctive Therapies in Mechanically Ventilated Patients with Acute Respiratory Distress Syndrome

Neuromuscular blocking agents (NMBAs) and prone position (PP) are two major adjunctive therapies that can improve outcome in moderate-to-severe acute respiratory distress syndrome. NMBA should be used once lung-protective mechanical ventilation has been set, for 48 hours or less and as a continuous intravenous infusion. PP should be used as early as possible for long sessions; in COVID-19 its use has exploded. In nonintubated patients, PP might reduce the rate of intubation but not mortality. The goal of this article is to perform a narrative review on the pathophysiological rationale, the clinical effects, and the clinical use and recommendations of both NMBA and PP.

Prone positioning improves ventilation-perfusion matching assessed by electrical impedance tomography in patients with ARDS: a prospective physiological study

BACKGROUND

The physiological effects of prone ventilation in ARDS patients have been discussed for a long time but have not been fully elucidated. Electrical impedance tomography (EIT) has emerged as a tool for bedside monitoring of pulmonary ventilation and perfusion, allowing the opportunity to obtain data. This study aimed to investigate the effect of prone positioning (PP) on ventilation-perfusion matching by contrast-enhanced EIT in patients with ARDS.

DESIGN

Monocenter prospective physiologic study.

SETTING

University medical ICU.

PATIENTS

Ten mechanically ventilated ARDS patients who underwent PP.

INTERVENTIONS

We performed EIT evaluation at the initiation of PP, 3 h after PP initiation and the end of PP during the first PP session.

MEASUREMENTS AND MAIN RESULTS

The regional distribution of ventilation and perfusion was analyzed based on EIT images and compared to the clinical variables regarding respiratory and hemodynamic status. Prolonged prone ventilation improved oxygenation in the ARDS patients. Based on EIT measurements, the distribution of ventilation was homogenized and dorsal lung ventilation was significantly improved by PP administration, while the effect of PP on lung perfusion was relatively mild, with increased dorsal lung perfusion observed. The ventilation-perfusion matched region was found to increase and correlate with the increased PaO₂/FiO₂ by PP, which was attributed mainly to reduced shunt in the lung.

CONCLUSIONS

Prolonged prone ventilation increased dorsal ventilation and perfusion, which resulted in improved ventilation-perfusion matching and oxygenation.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT04725227. Registered on 25 January 2021.

Effects of different positive end-expiratory pressure titration strategies during prone positioning in patients with acute respiratory distress syndrome: a prospective interventional study

Background

Prone positioning in combination with the application of low tidal volume and adequate positive end-expiratory pressure (PEEP) improves survival in patients with moderate to severe acute respiratory distress syndrome (ARDS). However, the effects of PEEP on end-expiratory transpulmonary pressure (Ptp_exp) during prone positioning require clarification. For this purpose, the effects of three different PEEP titration strategies on Ptp_exp, respiratory mechanics, mechanical power, gas exchange, and hemodynamics were evaluated comparing supine and prone positioning.

Methods

In forty consecutive patients with moderate to severe ARDS protective ventilation with PEEP titrated according to three different titration strategies was evaluated during supine and prone positioning: (A) ARDS Network recommendations (PEEP_ARDSNetwork), (B) the lowest static elastance of the respiratory system (PEEP_Estat,RS), and (C) targeting a positive Ptp_exp (PEEP_Ptpexp). The primary endpoint was to analyze whether Ptp_exp differed significantly according to PEEP titration strategy during supine and prone positioning.

Results

Ptp_exp increased progressively with prone positioning compared with supine positioning as well as with PEEP_Estat,RS and PEEP_Ptpexp compared with PEEP_ARDSNetwork (positioning effect p < 0.001, PEEP strategy effect p < 0.001). PEEP was lower during prone positioning with PEEP_Estat,RS and PEEP_Ptpexp (positioning effect p < 0.001, PEEP strategy effect p < 0.001). During supine positioning, mechanical power increased progressively with PEEP_Estat,RS and PEEP_Ptpexp compared with PEEP_ARDSNetwork, and prone positioning attenuated this effect (positioning effect p < 0.001, PEEP strategy effect p < 0.001). Prone compared with supine positioning significantly improved oxygenation (positioning effect p < 0.001, PEEP strategy effect p < 0.001) while hemodynamics remained stable in both positions.

Conclusions

Prone positioning increased transpulmonary pressures while improving oxygenation and hemodynamics in patients with moderate to severe ARDS when PEEP was titrated according to the ARDS Network lower PEEP table. This PEEP titration strategy minimized parameters associated with ventilator-induced lung injury induction, such as transpulmonary driving pressure and mechanical power. We propose that a lower PEEP strategy (PEEP_ARDSNetwork) in combination with prone positioning may be part of a lung protective ventilation strategy in patients with moderate to severe ARDS.

Trial registration

German Clinical Trials Register (DRKS00017449). Registered June 27, 2019. https://www.drks.de/drks_web/navigate.do?navigationId=trial.HTML&TRIAL_ID=DRKS00017449

Supplementary Information

The online version contains supplementary material available at 10.1186/s13054-022-03956-8.

Effects of Prone Position on Lung Recruitment and Ventilation-Perfusion Matching in Patients With COVID-19 Acute Respiratory Distress Syndrome

Prone positioning allows to improve oxygenation and decrease mortality rate in COVID-19–associated acute respiratory distress syndrome (C-ARDS). However, the mechanisms leading to these effects are not fully understood. The aim of this study is to assess the physiologic effects of pronation by the means of CT scan and electrical impedance tomography (EIT).

Prone Positioning in Acute Respiratory Distress Syndrome

Prone Positioning in ARDSCovid-19 has greatly expanded the use of prone positioning for patients with respiratory failure. Pearce and colleagues review the physiology of prone positioning and the evidence for its use, including in nonintubated patients.

Impact of exposure time in awake prone positioning on clinical outcomes of patients with COVID-19-related acute respiratory failure treated with high-flow nasal oxygen: a multicenter cohort study

Background

In patients with COVID-19-related acute respiratory failure (ARF), awake prone positioning (AW-PP) reduces the need for intubation in patients treated with high-flow nasal oxygen (HFNO). However, the effects of different exposure times on clinical outcomes remain unclear. We evaluated the effect of AW-PP on the risk of endotracheal intubation and in-hospital mortality in patients with COVID-19-related ARF treated with HFNO and analyzed the effects of different exposure times to AW-PP.

Methods

This multicenter prospective cohort study in six ICUs of 6 centers in Argentine consecutively included patients > 18 years of age with confirmed COVID-19-related ARF requiring HFNO from June 2020 to January 2021. In the primary analysis, the main exposure was awake prone positioning for at least 6 h/day, compared to non-prone positioning (NON-PP). In the sensitivity analysis, exposure was based on the number of hours receiving AW-PP. Inverse probability weighting–propensity score (IPW-PS) was used to adjust the conditional probability of treatment assignment. The primary outcome was endotracheal intubation (ETI); and the secondary outcome was hospital mortality.

Results

During the study period, 580 patients were screened and 335 were included; 187 (56%) tolerated AW-PP for [median (p25–75)] 12 (9–16) h/day and 148 (44%) served as controls. The IPW–propensity analysis showed standardized differences < 0.1 in all the variables assessed. After adjusting for other confounders, the OR (95% CI) for ETI in the AW-PP group was 0.36 (0.2–0.7), with a progressive reduction in OR as the exposure to AW-PP increased. The adjusted OR (95% CI) for hospital mortality in the AW-PP group ≥ 6 h/day was 0.47 (0.19–1.31). The exposure to prone positioning ≥ 8 h/d resulted in a further reduction in OR [0.37 (0.17–0.8)].

Conclusion

In the study population, AW-PP for ≥ 6 h/day reduced the risk of endotracheal intubation, and exposure ≥ 8 h/d reduced the risk of hospital mortality.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13054-021-03881-2.

Mechanisms of oxygenation responses to proning and recruitment in COVID-19 pneumonia

PURPOSE

This study aimed at investigating the mechanisms underlying the oxygenation response to proning and recruitment maneuvers in coronavirus disease 2019 (COVID-19) pneumonia.

METHODS

Twenty-five patients with COVID-19 pneumonia, at variable times since admission (from 1 to 3 weeks), underwent computed tomography (CT) lung scans, gas-exchange and lung-mechanics measurement in supine and prone positions at 5 cmH₂O and during recruiting maneuver (supine, 35 cmH₂O). Within the non-aerated tissue, we differentiated the atelectatic and consolidated tissue (recruitable and non-recruitable at 35 cmH₂O of airway pressure). Positive/negative response to proning/recruitment was defined as increase/decrease of PaO₂/FiO₂. Apparent perfusion ratio was computed as venous admixture/non aerated tissue fraction.

RESULTS

The average values of venous admixture and PaO₂/FiO₂ ratio were similar in supine-5 and prone-5. However, the PaO₂/FiO₂ changes (increasing in 65% of the patients and decreasing in 35%, from supine to prone) correlated with the balance between resolution of dorsal atelectasis and formation of ventral atelectasis (p = 0.002). Dorsal consolidated tissue determined this balance, being inversely related with dorsal recruitment (p = 0.012). From supine-5 to supine-35, the apparent perfusion ratio increased from 1.38 ± 0.71 to 2.15 ± 1.15 (p = 0.004) while PaO₂/FiO₂ ratio increased in 52% and decreased in 48% of patients. Non-responders had consolidated tissue fraction of 0.27 ± 0.1 vs. 0.18 ± 0.1 in the responding cohort (p = 0.04). Consolidated tissue, PaCO₂ and respiratory system elastance were higher in patients assessed late (all p < 0.05), suggesting, all together, "fibrotic-like" changes of the lung over time.

CONCLUSION

The amount of consolidated tissue was higher in patients assessed during the third week and determined the oxygenation responses following pronation and recruitment maneuvers.

New Frontiers in Functional and Molecular Imaging of the Acutely Injured Lung: Pathophysiological Insights and Research Applications

This review focuses on the advances in the understanding of the pathophysiology of ventilator-induced and acute lung injury that have been afforded by technological development of imaging methods over the last decades. Examples of such advances include the establishment of regional lung mechanical strain as a determinant of ventilator-induced lung injury, the relationship between alveolar recruitment and overdistension, the regional vs. diffuse nature of pulmonary involvement in acute respiratory distress syndrome (ARDS), the identification of the physiological determinants of the response to recruitment interventions, and the pathophysiological significance of metabolic alterations in the acutely injured lung. Taken together, these advances portray multimodality imaging as the next frontier to both advance knowledge of the pathophysiology of these conditions and to tailor treatment to the individual patient's condition.

Translational Role of Rodent Models to Study Ventilator-Induced Lung Injury

Mechanical ventilation is an important part of medical care in intensive care units and operating rooms to support respiration. While it is a critical component of medical care, it is well known that mechanical ventilation itself can be injurious to the lungs. Despite a large number of clinical and preclinical studies that have been done so far, there still exists a gap of knowledge regarding how to ventilate patients mechanically without increasing lung injury. Here, we will review what we have learned so far from preclinical and clinical studies and consider how to use preclinical models of ventilation-induced lung injury that better recapitulate the clinical scenarios.

Effect of prone versus supine position in COVID-19 patients: A systematic review and meta-analysis

STUDY OBJECTIVE

To review the effects of prone position and supine position on oxygenation parameters in patients with Coronavirus Disease 2019 (COVID-19).

DESIGN

Systematic review and meta-analysis of non-randomized trials.

PATIENTS

Databases of EMBASE, MEDLINE and CENTRAL were systematically searched from its inception until March 2021.

INTERVENTIONS

COVID-19 patients being positioned in the prone position either whilst awake or mechanically ventilated.

MEASUREMENTS

Primary outcomes were oxygenation parameters (PaO₂/FiO₂ ratio, PaCO₂, SpO₂). Secondary outcomes included the rate of intubation and mortality rate.

RESULTS

Thirty-five studies (n = 1712 patients) were included in this review. In comparison to the supine group, prone position significantly improved the PaO₂/FiO₂ ratio (study = 13, patients = 1002, Mean difference, MD 52.15, 95% CI 37.08 to 67.22; p < 0.00001) and SpO₂ (study = 11, patients = 998, MD 4.17, 95% CI 2.53 to 5.81; p ≤0.00001). Patients received prone position were associated with lower incidence of mortality (study = 5, patients = 688, Odd ratio, OR 0.44, 95% CI 0.24 to 0.80; p = 0.007). No significant difference was noted in the incidence of intubation rate (study = 5, patients = 626, OR 1.20, 95% CI 0.77 to 1.86; p = 0.42) between the supine and prone groups.

CONCLUSION

Our meta-analysis demonstrated that prone position improved PaO₂/FiO₂ ratio with better SpO₂ than supine position in COVID-19 patients. Given the limited number of studies with small sample size and substantial heterogeneity of measured outcomes, further studies are warranted to standardize the regime of prone position to improve the certainty of evidence. PROSPERO Registration: CRD42021234050.

Comparison of prone positioning and extracorporeal membrane oxygenation in acute respiratory distress syndrome: A multicenter cohort study and propensity-matched analysis

Background/Purpose

Both prone positioning and extracorporeal membrane oxygenation (ECMO) are used as rescue therapies for severe hypoxemia in patients with acute respiratory distress syndrome (ARDS). This study compared outcomes between patients with severe influenza pneumonia-related ARDS who received prone positioning and those who received ECMO.

Methods

This retrospective cohort study included eight tertiary referral centers in Taiwan. All patients who were diagnosed as having influenza pneumonia-related severe ARDS were enrolled between January and March 2016. We collected their demographic data and prone positioning and ECMO outcomes from medical records.

Results

In total, 263 patients diagnosed as having ARDS were included, and 65 and 53 of them received prone positioning and ECMO, respectively. The baseline PaO₂/FiO₂ ratio, Acute Physiology and Chronic Health Evaluation II score and Sequential Organ Failure Assessment score did not significantly differ between the two groups. The 60-day mortality rate was significantly higher in the ECMO group than in the prone positioning group (60% vs. 28%, p = 0.001). A significantly higher mortality rate was still observed in the ECMO group after propensity score matching (59% vs. 36%, p = 0.033). In the multivariate Cox regression analysis, usage of prone positioning or ECMO was the single independent predictor for 60-day mortality (hazard ratio: 2.177, p = 0.034).

Conclusion

While the patients receiving prone positioning had better outcome, the causality between prone positioning and the prognosis is unknown. However, the current data suggested that patients with influenza-related ARDS may receive prone positioning before ECMO support.

Diminishing Efficacy of Prone Positioning With Late Application in Evolving Lung Injury

OBJECTIVES

It is not known how lung injury progression during mechanical ventilation modifies pulmonary responses to prone positioning. We compared the effects of prone positioning on regional lung aeration in late versus early stages of lung injury.

DESIGN

Prospective, longitudinal imaging study.

SETTING

Research imaging facility at The University of Pennsylvania (Philadelphia, PA) and Medical and Surgical ICUs at Massachusetts General Hospital (Boston, MA).

SUBJECTS

Anesthetized swine and patients with acute respiratory distress syndrome (acute respiratory distress syndrome).

INTERVENTIONS

Lung injury was induced by bronchial hydrochloric acid (3.5 mL/kg) in 10 ventilated Yorkshire pigs and worsened by supine nonprotective ventilation for 24 hours. Whole-lung CT was performed 2 hours after hydrochloric acid (Day 1) in both prone and supine positions and repeated at 24 hours (Day 2). Prone and supine images were registered (superimposed) in pairs to measure the effects of positioning on the aeration of each tissue unit. Two patients with early acute respiratory distress syndrome were compared with two patients with late acute respiratory distress syndrome, using electrical impedance tomography to measure the effects of body position on regional lung mechanics.

MEASUREMENTS AND MAIN RESULTS

Gas exchange and respiratory mechanics worsened over 24 hours, indicating lung injury progression. On Day 1, prone positioning reinflated 18.9% ± 5.2% of lung mass in the posterior lung regions. On Day 2, position-associated dorsal reinflation was reduced to 7.3% ± 1.5% (p < 0.05 vs Day 1). Prone positioning decreased aeration in the anterior lungs on both days. Although prone positioning improved posterior lung compliance in the early acute respiratory distress syndrome patients, it had no effect in late acute respiratory distress syndrome subjects.

CONCLUSIONS

The effects of prone positioning on lung aeration may depend on the stage of lung injury and duration of prior ventilation; this may limit the clinical efficacy of this treatment if applied late.

Positive End-Expiratory Pressure, Pleural Pressure, and Regional Compliance during Pronation: An Experimental Study

Rationale: The physiological basis of lung protection and the impact of positive end-expiratory pressure (PEEP) during pronation in acute respiratory distress syndrome are not fully elucidated. Objectives: To compare pleural pressure (Ppl) gradient, ventilation distribution, and regional compliance between dependent and nondependent lungs, and investigate the effect of PEEP during supination and pronation. Methods: We used a two-hit model of lung injury (saline lavage and high-volume ventilation) in 14 mechanically ventilated pigs and studied supine and prone positions. Global and regional lung mechanics including Ppl and distribution of ventilation (electrical impedance tomography) were analyzed across PEEP steps from 20 to 3 cm H₂O. Two pigs underwent computed tomography scans: tidal recruitment and hyperinflation were calculated. Measurements and Main Results: Pronation improved oxygenation, increased Ppl, thus decreasing transpulmonary pressure for any PEEP, and reduced the dorsal-ventral pleural pressure gradient at PEEP < 10 cm H₂O. The distribution of ventilation was homogenized between dependent and nondependent while prone and was less dependent on the PEEP level than while supine. The highest regional compliance was achieved at different PEEP levels in dependent and nondependent regions in supine position (15 and 8 cm H₂O), but for similar values in prone position (13 and 12 cm H₂O). Tidal recruitment was more evenly distributed (dependent and nondependent), hyperinflation lower, and lungs cephalocaudally longer in the prone position. Conclusions: In this lung injury model, pronation reduces the vertical pleural pressure gradient and homogenizes regional ventilation and compliance between the dependent and nondependent regions. Homogenization is much less dependent on the PEEP level in prone than in supine positon.

Prone-Positioning for Severe Acute Respiratory Distress Syndrome Requiring Extracorporeal Membrane Oxygenation

OBJECTIVES

To determine the characteristics and outcomes of patients prone-positioned during extracorporeal membrane oxygenation for severe acute respiratory distress syndrome and lung CT pattern associated with improved respiratory system static compliance after that intervention.

DESIGN

Retrospective, single-center study over 8 years.

SETTINGS

Twenty-six bed ICU in a tertiary center.

MEASUREMENTS AND MAIN RESULTS

A propensity score-matched analysis compared patients with prone-positioning during extracorporeal membrane oxygenation and those without. An increase of the static compliance greater than or equal to 3 mL/cm H2O after 16 hours of prone-positioning defined prone-positioning responders. The primary outcome was the time to successful extracorporeal membrane oxygenation weaning within 90 days of postextracorporeal membrane oxygenation start, with death as a competing risk. Among 298 venovenous extracorporeal membrane oxygenation-treated adults with severe acute respiratory distress syndrome, 64 were prone-positioning extracorporeal membrane oxygenation. Although both propensity score-matched groups had similar extracorporeal membrane oxygenation durations, prone-positioning extracorporeal membrane oxygenation patients' 90-day probability of being weaned-off extracorporeal membrane oxygenation and alive was higher (0.75 vs 0.54, p = 0.03; subdistribution hazard ratio [95% CI], 1.54 [1.05-2.58]) and 90-day mortality was lower (20% vs 42%, p < 0.01) than that for no prone-positioning extracorporeal membrane oxygenation patients. Extracorporeal membrane oxygenation-related complications were comparable for the two groups. Patients without improved static compliance had higher percentages of nonaerated or poorly aerated ventral and medial-ventral lung regions (p = 0.047).

CONCLUSIONS

Prone-positioning during venovenous extracorporeal membrane oxygenation was safe and effective and was associated with a higher probability of surviving and being weaned-off extracorporeal membrane oxygenation at 90 days. Patients with greater normally aerated lung tissue in the ventral and medial-ventral regions on quantitative lung CT-scan performed before prone-positioning are more likely to improve their static compliance after that procedure during extracorporeal membrane oxygenation.

Therapeutic benefits of proning to improve pulmonary gas exchange in severe respiratory failure: focus on fundamentals of physiology

New Findings

What is the topic of this review?

The use of proning for improving pulmonary gas exchange in critically ill patients.

What advances does it highlight?

Proning places the lung in its ‘natural’ posture, and thus optimises the ventilation‐perfusion distribution, which enables lung protective ventilation and the alleviation of potentially life‐threatening hypoxaemia in COVID‐19 and other types of critical illness with respiratory failure.

Abstract

The survival benefit of proning patients with acute respiratory distress syndrome (ARDS) is well established and has recently been found to improve pulmonary gas exchange in patients with COVID‐19‐associated ARDS (CARDS). This review outlines the physiological implications of transitioning from supine to prone on alveolar ventilation‐perfusion (V˙A--Q˙) relationships during spontaneous breathing and during general anaesthesia in the healthy state, as well as during invasive mechanical ventilation in patients with ARDS and CARDS. Spontaneously breathing, awake healthy individuals maintain a small vertical (ventral‐to‐dorsal) V˙A/Q˙ ratio gradient in the supine position, which is largely neutralised in the prone position, mainly through redistribution of perfusion. In anaesthetised and mechanically ventilated healthy individuals, a vertical V˙A/Q˙ ratio gradient is present in both postures, but with better V˙A--Q˙ matching in the prone position. In ARDS and CARDS, the vertical V˙A/Q˙ ratio gradient in the supine position becomes larger, with intrapulmonary shunting in gravitationally dependent lung regions due to compression atelectasis of the dorsal lung. This is counteracted by proning, mainly through a more homogeneous distribution of ventilation combined with a largely unaffected high perfusion dorsally, and a consequent substantial improvement in arterial oxygenation. The data regarding proning as a therapy in patients with CARDS is still limited and whether the associated improvement in arterial oxygenation translates to a survival benefit remains unknown. Proning is nonetheless an attractive and lung protective manoeuvre with the potential benefit of improving life‐threatening hypoxaemia in patients with ARDS and CARDS.

Respiratory Physiology of Prone Positioning With and Without Inhaled Nitric Oxide Across the Coronavirus Disease 2019 Acute Respiratory Distress Syndrome Severity Spectrum

Supplemental Digital Content is available in the text.

IMPORTANCE:

Prone positioning improves clinical outcomes in moderate-to-severe acute respiratory distress syndrome and has been widely adopted for the treatment of patients with acute respiratory distress syndrome due to coronavirus disease 2019. Little is known about the effects of prone positioning among patients with less severe acute respiratory distress syndrome, obesity, or those treated with pulmonary vasodilators.

OBJECTIVES:

We characterize the change in oxygenation, respiratory system compliance, and dead-space-to-tidal-volume ratio in response to prone positioning in patients with coronavirus disease 2019 acute respiratory distress syndrome with a range of severities. A subset analysis of patients treated with inhaled nitric oxide and subsequent prone positioning explored the influence of pulmonary vasodilation on the physiology of prone positioning.

DESIGN, SETTING, AND PARTICIPANTS:

Retrospective cohort study of all consecutively admitted adult patients with acute respiratory distress syndrome due to coronavirus disease 2019 treated with mechanical ventilation and prone positioning in the ICUs of an academic hospital between March 11, 2020, and May 1, 2020.

MAIN OUTCOMES AND MEASURES:

Respiratory system mechanics and gas exchange during the first episode of prone positioning.

RESULTS:

Among 122 patients, median (interquartile range) age was 60 years (51–71 yr), median body mass index was 31.5 kg/m² (27–35 kg/m²), and 50 patients (41%) were female. The ratio of Pao₂ to Fio₂ improved with prone positioning in 90% of patients. Prone positioning was associated with a significant increase in the ratio of Pao₂ to Fio₂ (from median 149 [123–170] to 226 [169–268], p < 0.001) but no change in dead-space-to-tidal-volume ratio or respiratory system compliance. Supine ratio of Pao₂ to Fio₂, respiratory system compliance, positive end-expiratory pressure, and body mass index did not correlate with absolute change in the ratio of Pao₂ to Fio₂ with prone positioning. However, patients with ratio of Pao₂ to Fio₂ less than 150 experienced a greater relative improvement in oxygenation with prone positioning than patients with ratio of Pao₂ to Fio₂ greater than or equal to 150 (median percent change in ratio of Pao₂ to Fio₂ 62 [29–107] vs 30 [10–70], p = 0.002). Among 12 patients, inhaled nitric oxide prior to prone positioning was associated with a significant increase in the ratio of Pao₂ to Fio₂ (from median 136 [77–168] to 170 [138–213], p = 0.003) and decrease in dead-space-to-tidal-volume ratio (0.54 [0.49–0.58] to 0.46 [0.44–0.53], p = 0.001). Subsequent prone positioning in this subgroup further improved the ratio of Pao₂ to Fio₂ (from 145 [122–183] to 205 [150–232], p = 0.017) but did not change dead-space-to-tidal-volume ratio.

CONCLUSIONS AND RELEVANCE:

Prone positioning improves oxygenation across the acute respiratory distress syndrome severity spectrum, irrespective of supine respiratory system compliance, positive end-expiratory pressure, or body mass index. There was a greater relative benefit among patients with more severe disease. Prone positioning confers an additive benefit in oxygenation among patients treated with inhaled nitric oxide.

Unmatched ventilation and perfusion measured by electrical impedance tomography predicts the outcome of ARDS

Background

In acute respiratory distress syndrome (ARDS), non-ventilated perfused regions coexist with non-perfused ventilated regions within lungs. The number of unmatched regions might reflect ARDS severity and affect the risk of ventilation-induced lung injury. Despite pathophysiological relevance, unmatched ventilation and perfusion are not routinely assessed at the bedside. The aims of this study were to quantify unmatched ventilation and perfusion at the bedside by electrical impedance tomography (EIT) investigating their association with mortality in patients with ARDS and to explore the effects of positive end-expiratory pressure (PEEP) on unmatched ventilation and perfusion in subgroups of patients with different ARDS severity based on PaO₂/FiO₂ and compliance.

Methods

Prospective observational study in 50 patients with mild (36%), moderate (46%), and severe (18%) ARDS under clinical ventilation settings. EIT was applied to measure the regional distribution of ventilation and perfusion using central venous bolus of saline 5% during end-inspiratory pause. We defined unmatched units as the percentage of only ventilated units plus the percentage of only perfused units.

Results

Percentage of unmatched units was significantly higher in non-survivors compared to survivors (32[27–47]% vs. 21[17–27]%, p < 0.001). Percentage of unmatched units was an independent predictor of mortality (OR 1.22, 95% CI 1.07–1.39, p = 0.004) with an area under the ROC curve of 0.88 (95% CI 0.79–0.97, p < 0.001). The percentage of ventilation to the ventral region of the lung was higher than the percentage of ventilation to the dorsal region (32 [27–38]% vs. 18 [13–21]%, p < 0.001), while the opposite was true for perfusion (28 [22–38]% vs. 36 [32–44]%, p < 0.001).

Higher percentage of only perfused units was correlated with lower dorsal ventilation (r =  − 0.486, p < 0.001) and with lower PaO₂/FiO₂ ratio (r =  − 0.293, p = 0.039).

Conclusions

EIT allows bedside assessment of unmatched ventilation and perfusion in mechanically ventilated patients with ARDS. Measurement of unmatched units could identify patients at higher risk of death and could guide personalized treatment.

The efficacy and tolerance of prone positioning in non-intubation patients with acute hypoxemic respiratory failure and ARDS: a meta-analysis

Background and aims:

The application of prone positioning with acute hypoxemic respiratory failure (AHRF) or acute respiratory distress syndrome (ARDS) in non-intubation patients is increasing gradually, applying prone positioning for more high-flow nasal oxygen therapy (HFNC) and non-invasive ventilation (NIV) patients. This meta-analysis evaluates the efficacy and tolerance of prone positioning combined with non-invasive respiratory support in patients with AHRF or ARDS.

Methods:

We searched randomized controlled trials (RCTs) (prospective or retrospective cohort studies, RCTs and case series) published in PubMed, EMBASE and the Cochrane Central Register of Controlled Trials from 1 January 2000 to 1 July 2020. We included studies that compared prone and supine positioning with non-invasive respiratory support in awake patients with AHRF or ARDS. The meta-analyses used random effects models. The methodological quality of the RCTs was evaluated using the Newcastle–Ottawa quality assessment scale.

Results:

A total of 16 studies fulfilled selection criteria and included 243 patients. The aggregated intubation rate and mortality rate were 33% [95% confidence interval (CI): 0.26–0.42, I² = 25%], 4% (95% CI: 0.01–0.07, I² = 0%), respectively, and the intolerance rate was 7% (95% CI: 0.01–0.12, I² = 5%). Prone positioning increased PaO₂/FiO₂ [mean difference (MD) = 47.89, 95% CI: 28.12–67.66; p < 0.00001, I² = 67%] and SpO₂ (MD = 4.58, 95% CI: 1.35–7.80, p = 0.005, I² = 97%), whereas it reduced respiratory rate (MD = −5.01, 95% CI: −8.49 to −1.52, p = 0.005, I² = 85%). Subgroup analyses demonstrated that the intubation rate of shorter duration prone (⩽5 h/day) and longer duration prone (>5 h/day) were 34% and 21%, respectively; and the mortality rate of shorter duration prone (⩽5 h/day) and longer duration prone (>5 h/day) were 6% and 0%, respectively. PaO₂/FiO₂ and SpO₂ were significantly improved in COVID-19 patients and non-COVID-19 patients.

Conclusion:

Prone positioning could improve the oxygenation and reduce respiratory rate in both COVID-19 patients and non-COVID-19 patients with non-intubated AHRF or ARDS.

The reviews of this paper are available via the supplemental material section.

Association Between Sleep Characteristics and Asthma Control in Middle-Aged and Older Adults: A Prospective Cohort Study

Background

Nocturnal asthma symptoms are a well-known feature of sleep disturbance. However, there are few reports on the association between sleep-related characteristics and asthma exacerbation. The aim of the current prospective observational study was to explore the factors while sleeping associated with future asthma exacerbation.

Materials and Methods

At baseline, adult asthmatics underwent home sleep monitoring by a Watch-PAT instrument and then they were prospectively followed-up for the occurrence of exacerbations. The number of asthma exacerbation was observed over a period of one year, and multivariable analyses of the factors associated with asthma exacerbation were performed.

Results

A total of 62 asthmatic subjects were enrolled (mean age 62.1 years), 59 of whom were finally included in the prospective observational study. Obstructive sleep apnea (defined by an apnea-hypopnea index based on peripheral arterial tone more than 5 times/hour) were observed in 81% of the subjects. During the one-year monitoring period, 14 of the 59 subjects (24%) used occasional systemic corticosteroids for their exacerbation asthma (worsened group) while the other 45 subjects did not experience asthma exacerbation (stable group). A comparison of the baseline clinical characteristics and sleep-related data between the two groups, mean forced expiratory volume one second percent (FEV₁/FVC), mean baseline Asthma Control Test (ACT) score, median pAHI value, and median oxygen desaturation index value were significantly lower in the worsened group than those in the stable group. Additionally, mean prevalence of the left lateral decubitus (LLD) position in sleep monitoring were significantly higher in the worsened group than that in the stable group. Among the independent variables, baseline asthma severity, ACT score, and the LLD position showed significant associations with asthma exacerbation.

Discussion/Conclusion

The present study identified that sleeping in the LLD position was also associated with asthma exacerbation.

Prone versus Supine Position for Lung Ultrasound in Neonates with Respiratory Distress

OBJECTIVE

To study the feasibility of lung ultrasound (LUS) in prone position and to compare it with supine position in neonates with respiratory distress.

STUDY DESIGN

Neonates ≥ 29 weeks of gestational age with respiratory distress requiring respiratory support within first 12 hours of life were enrolled prospectively. First LUS (fLUS) was done in the position infant was nursed (supine or prone), infant's position changed, a second LUS (sLUS) was performed immediately and a third LUS (tLUS) was done 1 to 2 hours later. Primary outcome was the comparison of LUS scores (LUSsc) between fLUS and sLUS.

RESULTS

Sixty-four neonates were enrolled. Common respiratory diagnoses were transient tachypnea of newborn (TTN; 53%) and respiratory distress syndrome (RDS; 41%). LUSsc was different between fLUS and sLUS (fLUSsc 6 [interquatile range: 4, 7] vs. sLUSsc 7 [4, 10], p < 0.001), while there was no difference between the fLUS and tLUS (fLUSsc 6 [4, 7] vs. tLUSsc 5 [3, 7], p = 0.43). Subgroup analysis confirmed similar findings in neonates with TTN, while in babies with RDS, all the three LUSsc were similar.

CONCLUSION

LUS is feasible in prone position in neonates. LUS scores were higher immediately after a change in position but were similar to baseline 1 hour after the change in position.