Beneficial hemodynamic effects of prone positioning in patients with acute respiratory distress syndrome

The effect of prone positioning on ventilator parameters, blood gas levels, and ventilator-associated pneumonia in intensive care unit patients: a randomized controlled trial

OBJECTIVES

This study was planned to compare the prone position and non-prone position groups and to evaluate arterial blood gas results, mechanical ventilator values and ventilator-associated pneumonia (VAP) status before, during, and after patients were brought back to the non-prone position.

DESIGN

This study is a randomized controlled trial with a parallel-group design and a 1:1 allocation ratio. A block randomisation method was used to ensure balanced allocation between two groups.

SETTING

The research was conducted in the 14-bed and 26-bed general ICUs of two private hospitals on the European side of Istanbul.

PARTICIPANTS

The 94 eligible participants were randomly divided into two groups. 52 participants were assigned to the prone position group, while 42 participants were assigned to the non-prone position group, which served as the control group. In the end, 40 participants were in each group.

INTERVENTION

The intervention involved placing patients in the prone position and monitoring their arterial blood gas results, mechanical ventilator values, and VAP status at multiple stages: before, during, and after returning them to the non-prone position. Each patient was followed for a minimum of 5 days.

RESULTS

The majority of the participants were male (51.2%) and aged 45-64 (48.8%). The comparison of experimental and control groups indicated statistically significant difference in saturation, FiO₂, inspiratory-expiratory tidal volume, and blood gas levels of the patients in the treatment group (p = 0.001; p < 0.01).

CONCLUSIONS

The change in the experimental group was greater than in the control group. In conclusion, the mechanical ventilator parameters and blood gas levels of the patients in the treatment group were better than those of the patients in the control group. It is recommended as an effective practice in patients receiving prone position mechanical ventilation (MV).

CLINICAL TRIAL REGISTRATION NUMBER AND REGISTRATION DATE

NCT05760716/ March 6, 2023 (This trial was registered retrospectively at ClinicalTrials.gov (Registration Number: NCT05760716) after its completion due to demanded revisions. The integrity of the data and adherence to the study protocol were ensured throughout. The trial adhered to ethical standards (ethics committee approval, informed consent) even if it was not registered prospectively).

Navigating Heart-Lung Interactions in Mechanical Ventilation: Pathophysiology, Diagnosis, and Advanced Management Strategies in Acute Respiratory Distress Syndrome and Beyond

Patients in critical condition who require mechanical ventilation experience intricate interactions between their respiratory and cardiovascular systems. These complex interactions are crucial for clinicians to understand as they can significantly influence therapeutic decisions and patient outcomes. A deep understanding of heart-lung interactions is essential, particularly under the stress of mechanical ventilation, where the right ventricle plays a pivotal role and often becomes a primary concern. Positive pressure ventilation, commonly used in mechanical ventilation, impacts right and left ventricular pre- and afterload as well as ventricular interplay. The right ventricle is especially susceptible to these changes, and its function can be critically affected, leading to complications such as right heart failure. Clinicians must be adept at recognizing and managing these interactions to optimize patient care. This perspective will analyze this matter comprehensively, covering the pathophysiology of these interactions, the monitoring of heart-lung dynamics using the latest methods (including ECHO), and management and treatment strategies for related conditions. In particular, the analysis will delve into the efficacy and limitations of various treatment modalities, including pharmaceutical interventions, nuanced ventilator management strategies, and advanced devices such as extracorporeal membrane oxygenation (ECMO). Each approach will be examined for its impact on optimizing right ventricular function, mitigating complications, and ultimately improving patient outcomes in the context of mechanical ventilation.

Heart-lung crosstalk in acute respiratory distress syndrome

Acute Respiratory Distress Syndrome (ARDS) is initiated by a primary insult that triggers a cascade of pathological events, including damage to lung epithelial and endothelial cells, extracellular matrix disruption, activation of immune cells, and the release of pro-inflammatory mediators. These events lead to increased alveolar-capillary barrier permeability, resulting in interstitial/alveolar edema, collapse, and subsequent hypoxia and hypercapnia. ARDS not only affects the lungs but also significantly impacts the cardiovascular system. We conducted a comprehensive literature review on heart-lung crosstalk in ARDS, focusing on the pathophysiology, effects of mechanical ventilation, hypoxemia, and hypercapnia on cardiac function, as well as ARDS secondary to cardiac arrest and cardiac surgery. Mechanical ventilation, essential for ARDS management, can increase intrathoracic pressure, decrease venous return and right ventricle preload. Moreover, acidemia and elevations in transpulmonary pressures with mechanical ventilation both increase pulmonary vascular resistance and right ventricle afterload. Cardiac dysfunction can exacerbate pulmonary edema and impair gas exchange, creating a vicious cycle, which hinders both heart and lung therapy. In conclusion, understanding the heart-lung crosstalk in ARDS is important to optimize therapeutic strategies. Future research should focus on elucidating the precise mechanisms underlying this interplay and developing targeted interventions that address both organs simultaneously.

Comparison of Standard and Prone-Position Electrocardiograms in COVID-19 Patients With Pulmonary Complications: Correlations and Implications

BACKGROUND

Previous research highlighted variability in electrocardiogram (ECG) readings across patient positions, particularly in the context of COVID-19 patients with pulmonary complications requiring prone positioning as part of the treatment.

OBJECTIVE

This study aimed to elucidate the effects of prone positioning on ECG parameters and explore its association with the severity of COVID-19.

METHODS

A prospective cohort study involved 60 patients diagnosed with COVID-19 and presenting pulmonary complications. ECGs were recorded in both supine and prone positions, and analyzed for various parameters including heart rate, QRS axis, and QTc interval. Clinical severity was assessed using APACHE II scores and SpO2/FiO2 ratios.

RESULTS

Prone positioning led to an increase in heart rate (mean difference: 2.100, 95% CI: 0.471-3.729, p = 0.012), with minor shifts in the QRS axis. Heart rate and QRS axis demonstrated strong positive correlations between positions, with Pearson's correlation coefficients of 0.927 and 0.894, respectively. The study also found a significant association between prolonged QTc intervals in the prone position and elevated APACHE II scores, with a relative risk of 10.75 (95% CI: 1.82-63.64, p = 0.008).

CONCLUSIONS

The prone positioning caused minor yet significant changes in heart rate and QRS axis. The correlation of prolonged QTc intervals in the prone position with higher APACHE II scores suggests the prognostic relevance of prone ECG in COVID-19 patients. However, further research is needed to fully understand the clinical implications and mechanisms of these findings.

Definition and management of right ventricular injury in adult patients receiving extracorporeal membrane oxygenation for respiratory support using the Delphi method: a PRORVnet study. Expert position statements

PURPOSE

Veno-venous extracorporeal membrane oxygenation (VV-ECMO) is an integral part of the management algorithm of patients with severe respiratory failure refractory to evidence-based conventional treatments. Right ventricular injury (RVI) pertaining to abnormalities in the dimensions and/or function of the right ventricle (RV) in the context of VV-ECMO significantly influences mortality. However, in the absence of a universally accepted RVI definition and evidence-based guidance for the management of RVI in this very high-risk patient cohort, variations in clinical practice continue to exist.

METHODS

Following a systematic search of the literature, an international Steering Committee consisting of eight healthcare professionals involved in the management of patients receiving ECMO identified domains and knowledge gaps pertaining to RVI definition and management where the evidence is limited or ambiguous. Using a Delphi process, an international panel of 52 Experts developed Expert position statements in those areas. The process also conferred RV-centric overarching open questions for future research. Consensus was defined as achieved when 70% or more of the Experts agreed or disagreed on a Likert-scale statement or when 80% or more of the Experts agreed on a particular option in multiple-choice questions.

RESULTS

The Delphi process was conducted through four rounds and consensus was achieved on 31 (89%) of 35 statements from which 24 Expert position statements were derived. Expert position statements provided recommendations for RVI nomenclature in the setting of VV-ECMO, a multi-modal diagnostic approach to RVI, the timing and parameters of diagnostic echocardiography, and VV-ECMO settings during RVI assessment and management. Consensus was not reached on RV-protective driving pressure thresholds or the effect of prone positioning on patient-centric outcomes.

CONCLUSION

The proposed definition of RVI in the context of VV-ECMO needs to be validated through a systematic aggregation of data across studies. Until further evidence emerges, the Expert position statements can guide informed decision-making in the management of these patients.

Guideline on positioning and early mobilisation in the critically ill by an expert panel

A scientific panel was created consisting of 23 interdisciplinary and interprofessional experts in intensive care medicine, physiotherapy, nursing care, surgery, rehabilitative medicine, and pneumology delegated from scientific societies together with a patient representative and a delegate from the Association of the Scientific Medical Societies who advised methodological implementation. The guideline was created according to the German Association of the Scientific Medical Societies (AWMF), based on The Appraisal of Guidelines for Research and Evaluation (AGREE) II. The topics of (early) mobilisation, neuromuscular electrical stimulation, assist devices for mobilisation, and positioning, including prone positioning, were identified as areas to be addressed and assigned to specialist expert groups, taking conflicts of interest into account. The panel formulated PICO questions (addressing the population, intervention, comparison or control group as well as the resulting outcomes), conducted a systematic literature review with abstract screening and full-text analysis and created summary tables. This was followed by grading the evidence according to the Oxford Centre for Evidence-Based Medicine 2011 Levels of Evidence and a risk of bias assessment. The recommendations were finalized according to GRADE and voted using an online Delphi process followed by a final hybrid consensus conference. The German long version of the guideline was approved by the professional associations. For this English version an update of the systematic review was conducted until April 2024 and recommendation adapted based on new evidence in systematic reviews and randomized controlled trials. In total, 46 recommendations were developed and research gaps addressed.

Impact of intensive prone position therapy on outcomes in intubated patients with ARDS related to COVID-19

BACKGROUND

Previous retrospective research has shown that maintaining prone positioning (PP) for an average of 40 h is associated with an increase of survival rates in intubated patients with COVID-19-related acute respiratory distress syndrome (ARDS). This study aims to determine whether a cumulative PP duration of more than 32 h during the first 2 days of intensive care unit (ICU) admission is associated with increased survival compared to a cumulative PP duration of 32 h or less.

METHODS

This study is an ancillary analysis from a previous large international observational study involving intubated patients placed in PP in the first 48 h of ICU admission in 149 ICUs across France, Belgium and Switzerland. Given that PP is recommended for a 16-h daily duration, intensive PP was defined as a cumulated duration of more than 32 h during the first 48 h, whereas standard PP was defined as a duration equal to or less than 32 h. Patients were followed-up for 90 days. The primary outcome was mortality at day 60. An Inverse Probability Censoring Weighting (IPCW) Cox model including a target emulation trial method was used to analyze the data.

RESULTS

Out of 2137 intubated patients, 753 were placed in PP during the first 48 h of ICU admission. The intensive PP group (n = 79) had a median PP duration of 36 h, while standard PP group (n = 674) had a median of 16 h during the first 48 h. Sixty-day mortality rate in the intensive PP group was 39.2% compared to 38.7% in the standard PP group (p = 0.93). Twenty-eight-day and 90-day mortality as well as the ventilator-free days until day 28 were similar in both groups. After IPCW, there was no significant difference in mortality at day 60 between the two-study groups (HR 0.95 [0.52-1.74], p = 0.87 and HR 1.1 [0.77-1.57], p = 0.61 in complete case analysis or in multiple imputation analysis, respectively).

CONCLUSIONS

This secondary analysis of a large multicenter European cohort of intubated patients with ARDS due to COVID-19 found that intensive PP during the first 48 h did not provide a survival benefit compared to standard PP.

Haemodynamic changes during prone versus supine position in patients with COVID-19 acute respiratory distress syndrome

BACKGROUND

Prone positioning improves oxygenation in patients with acute respiratory distress syndrome (ARDS) secondary to COVID-19. However, its haemodynamic effects are poorly understood.

OBJECTIVES

The objective of this study was to investigate the acute haemodynamic changes associated with prone position in mechanically ventilated patients with COVID-19 ARDS. The primary objective was to describe changes in cardiac index with prone position. The secondary objectives were to describe changes in mean arterial pressure, FiO2, PaO2/FiO2 ratio, and oxygen delivery (DO2) with prone position.

METHODS

We performed this cohort-embedded study in an Australian intensive care unit, between September and November 2021. We included adult patients with severe COVID-19 ARDS, requiring mechanical ventilation and prone positioning for respiratory failure. We placed patients in the prone position for 16 h per session. Using pulse contour technology, we collected haemodynamic data every 5 min for 2 h in the supine position and for 2 h in the prone position consecutively.

RESULTS

We studied 18 patients. Cardiac index, stroke volume index, and mean arterial pressure increased significantly in the prone position compared to supine position. The mean cardiac index was higher in the prone group than in the supine group by 0.44 L/min/m2 (95% confidence interval, 0.24 to 0.63) (P < 0.001). FiO2 requirement decreased significantly in the prone position (P < 0.001), with a significant increase in PaO2/FiO2 ratio (P < 0.001). DO2 also increased significantly in the prone position, from a median DO2 of 597 mls O2/min (interquartile range, 504 to 931) in the supine position to 743 mls O2/min (interquartile range, 604 to 1075) in the prone position (P < 0.001).

CONCLUSION

Prone position increased the cardiac index, mean arterial pressure, and DO2 in invasively ventilated patients with COVID-19 ARDS. These changes may contribute to improved tissue oxygenation and improved outcomes observed in trials of prone positioning.

Effect of prone position on right ventricular dysfunction due to pulmonary embolism assessed by speckle tracking echocardiography

Prone position has shown beneficial hemodynamic effects in patients with right ventricular dysfunction associated with acute respiratory distress syndrome decreasing the right ventricle afterload. We describe the case of a 57-year-old man with right ventricular dysfunction associated with pulmonary thromboembolism with severe hypoxemia that required mechanical ventilation in prone position. With this maneuver, we verified an improvement not only in his oxygenation, but also in his right ventricular function assessed with speckle tracking echocardiography. Our case shows the potential beneficial effect of the prone position maneuver in severely hypoxemic patients with right ventricular dysfunction associated with pulmonary thromboembolism.

Feasibility of Prone Positioning for Brain-injured Patients with Severe Acute Respiratory Distress Syndrome: A Systematic Review and Pilot Study (ProBrain)

BACKGROUND

Prone position is a key component to treat hypoxemia in patients with severe acute respiratory distress syndrome. However, most studies evaluating it exclude patients with brain injuries without any medical evidence.

METHODS

This study includes a systematic review to determine whether brain-injured patients were excluded in studies evaluating prone position on acute respiratory distress syndrome; a prospective study including consecutive brain-injured patients needing prone position. The primary endpoint was the evaluation of cerebral blood flow using transcranial Doppler after prone positioning. Secondary outcomes were intracranial pressure, cerebral perfusion pressure, and tissue oxygen pressure.

RESULTS

From 8,183 citations retrieved, 120 studies were included in the systematic review. Among them, 90 studies excluded brain-injured patients (75%) without any justification, 16 included brain-injured patients (4 randomized, 7 nonrandomized studies, 5 retrospective), and 14 did not retrieve brain-injured data. Eleven patients were included in the authors' pilot study. No reduction of cerebral blood flow surrogates was observed during prone positioning, with diastolic speed values (mean ± SD) ranging from 37.7 ± 16.2 cm/s to 45.2 ± 19.3 cm/s for the right side (P = 0.897) and 39.6 ± 18.2 cm/s to 46.5 ± 21.3 cm/s for the left side (P = 0.569), and pulsatility index ranging from 1.14 ± 0.31 to 1.0 ± 0.32 for the right side (P = 0.145) and 1.14 ± 0.31 to 1.02 ± 0.2 for the left side (P = 0.564) before and during prone position.

CONCLUSIONS

Brain-injured patients are largely excluded from studies evaluating prone position in acute respiratory distress syndrome. However, cerebral blood flow seems not to be altered considering increasing of mean arterial pressure during the session. Systematic exclusion of brain-injured patients appears to be unfounded, and prone position, while at risk in brain-injured patients, should be evaluated on these patients to review recommendations, considering close monitoring of neurologic and hemodynamic parameters.

EDITOR’S PERSPECTIVE

The place of positive end expiratory pressure in ventilator-induced lung injury generation

PURPOSE OF REVIEW

Describe the rationale for concern and accumulating pathophysiologic evidence regarding the adverse effects of high-level positive end expiratory pressure (PEEP) on excessive mechanical stress and ventilator-induced lung injury (VILI).

RECENT FINDINGS

Although the inclusion of PEEP in numerical estimates of mechanical power may be theoretically debated, its potential to increase stress, strain, and mean airway pressure are not. Recent laboratory data in a variety of animal models demonstrate that higher levels of PEEP coupled with additional fluids needed to offset its impediment of hemodynamic function are associated with increased VILI. Moreover, counteracting end-tidal hyperinflation by external chest wall pressure may paradoxically improve respiratory mechanics, indicating that lower PEEP helps protect the small 'baby lung' of advanced acute respiratory distress syndrome (ARDS).

SUMMARY

The potentially adverse effects of PEEP on VILI can be considered in three broad categories. First, the contribution of PEEP to total mechanical energy expressed through mechanical power, raised mean airway pressure, and end-tidal hyperinflation; second, the hemodynamic consequences of altered cardiac loading, heightened pulmonary vascular stress and total lung water; and third, the ventilatory consequences of compromised carbon dioxide eliminating efficiency. Minimizing ventilation demands, optimized body positioning and care to avoid unnecessary PEEP are central to lung protection in all stages of ARDS.

Low-flow ECCO2R conjoined with renal replacement therapy platform to manage pulmonary vascular dysfunction with refractory hypercapnia in ARDS

Background

Hypercapnia worsens lung vascular dysfunction during acute respiratory distress syndrome (ARDS). We tested whether an extracorporeal carbon dioxide removal (ECCO2R) device based on a renal replacement therapy platform (Prismalung®) may reduce PaCO2 and alleviate lung vascular dysfunction in ARDS patients with refractory hypercapnia.

Methods

We planned to prospectively include 20 patients with moderate-to-severe ARDS, pulmonary vascular dysfunction on echocardiography, and PaCO2 ≥ 48 mmHg despite instrumental dead space reduction and the increase in respiratory rate. Hemodynamics, echocardiography, respiratory mechanics, and arterial blood gases were recorded at 2 (H2), 6 (H6) and 24 (H24) hours as ECCO2R treatment was continued for at least 24 h.

Results

Only eight patients were included, and the study was stopped due to worldwide shortage of ECCO2R membranes and the pandemic. Only one patient fulfilled the primary endpoint criterion (decrease in PaCO2 of more than 20 %) at H2, but this objective was achieved in half of patients (n = 4) at H6. The percentage of patients with a PaCO2 value < 48 mmHg increased with time, from 0/8 (0 %) at H0, to 3/8 (37.5 %) at H2 and 4/8 (50 %) at H6 (p = 0.04). There was no major change in hemodynamic and echocardiographic variables with ECCO2R, except for a significant decrease in heart rate. ECCO2R was prematurely discontinued before H24 in five (62.5 %) patients, due to membrane clotting in all cases.

Conclusions

This pilot study testing showed a narrow efficacy and high rate of membrane thrombosis with the first version of the system. Improved versions should be tested in future trials.

Trial registration

Registered at clinicaltrials.gov, identifier: NCT03303807, Registered: October 6, 2017, https://clinicaltrials.gov/ct2/show/NCT03303807.

Prone Positioning and Molecular Biomarkers in COVID and Non-COVID ARDS: A Narrative Review

Prone positioning (PP) represents a therapeutic intervention with the proven capacity of ameliorating gas exchanges and ventilatory mechanics indicated in acute respiratory distress syndrome (ARDS). When PP is selectively applied to moderate-severe cases of ARDS, it sensitively affects clinical outcomes, including mortality. After the COVID-19 outbreak, clinical application of PP peaked worldwide and was applied in 60% of treated cases, according to large reports. Research on this topic has revealed many physiological underpinnings of PP, focusing on regional ventilation redistribution and the reduction of parenchymal stress and strain. However, there is a lack of evidence on biomarkers behavior in different phases and phenotypes of ARDS. Patients response to PP are, to date, decided on PaO2/FiO2 ratio improvement, whereas scarce data exist on biomarker tracking during PP. The purpose of this review is to explore current evidence on the clinical relevance of biomarkers in the setting of moderate-severe ARDS of different etiologies (i.e., COVID and non-COVID-related ARDS). Moreover, this review focuses on how PP may modulate biomarkers and which biomarkers may have a role in outcome prediction in ARDS patients.

Prone Positioning During Extracorporeal Membrane Oxygenation in Patients With Severe ARDS: The PRONECMO Randomized Clinical Trial

Importance

Prone positioning may improve outcomes in patients with severe acute respiratory distress syndrome (ARDS), but it is unknown whether prone positioning improves clinical outcomes among patients with ARDS who are undergoing venovenous extracorporeal membrane oxygenation (VV-ECMO) compared with supine positioning.

Objective

To test whether prone positioning vs supine positioning decreases the time to successful ECMO weaning in patients with severe ARDS supported by VV-ECMO.

Design, Setting, and Participants

Randomized clinical trial of patients with severe ARDS undergoing VV-ECMO for less than 48 hours at 14 intensive care units (ICUs) in France between March 3, 2021, and December 7, 2021.

Interventions

Patients were randomized 1:1 to prone positioning (at least 4 sessions of 16 hours) (n = 86) or to supine positioning (n = 84).

Main Outcomes and Measures

The primary outcome was time to successful ECMO weaning within 60 days following randomization. Secondary outcomes included ECMO and mechanical ventilation-free days, ICU and hospital length of stay, skin pressure injury, serious adverse events, and all-cause mortality at 90-day follow-up.

Results

Among 170 randomized patients (median age, 51 [IQR, 43-59] years; n = 60 women [35%]), median respiratory system compliance was 15.0 (IQR, 10.7-20.6) mL/cm H2O; 159 patients (94%) had COVID-19-related ARDS; and 164 (96%) were in prone position before ECMO initiation. Within 60 days of enrollment, 38 of 86 patients (44%) had successful ECMO weaning in the prone ECMO group compared with 37 of 84 (44%) in the supine ECMO group (risk difference, 0.1% [95% CI, -14.9% to 15.2%]; subdistribution hazard ratio, 1.11 [95% CI, 0.71-1.75]; P = .64). Within 90 days, no significant difference was observed in ECMO duration (28 vs 32 days; difference, -4.9 [95% CI, -11.2 to 1.5] days; P = .13), ICU length of stay, or 90-day mortality (51% vs 48%; risk difference, 2.4% [95% CI, -13.9% to 18.6%]; P = .62). No serious adverse events were reported during the prone position procedure.

Conclusions and Relevance

Among patients with severe ARDS supported by VV-ECMO, prone positioning compared with supine positioning did not significantly reduce time to successful weaning of ECMO.

Trial Registration

ClinicalTrials.gov Identifier: NCT04607551.

Effects of prone positioning on ARDS outcomes of trauma and surgical patients: a systematic review and meta-analysis

BACKGROUND

Prone position is an option for rescue therapy for acute respiratory distress syndrome. However, there are limited relevant data among trauma and surgical patients, who may be at increased risk for complications following position changes. This study aimed to identify the benefits and risks of proning in this patient subgroup.

METHODS

Follow the PRISMA 2020, MEDLINE and EMBASE database searches were conducted. Additional search of relevant primary literature and review articles was also performed. A random effects model was used to estimate the PF ratio, mortality rate, mechanical ventilator days, and intensive care unit length of stay using Review Manager 5.4.1 software.

RESULTS

Of 1,128 studies, 15 articles were included in this meta-analysis. The prone position significantly improved the PF ratio compared with the supine position (mean difference, 79.26; 95% CI, 53.38 to 105.13). The prone position group had a statistically significant mortality benefit (risk ratio [RR], 0.48; 95% CI, 0.35 to 0.67). Although there was no significant difference in the intensive care unit length of stay, the prone position significantly decreased mechanical ventilator days (-2.59; 95% CI, -4.21 to -0.97). On systematic review, minor complications were frequent, especially facial edema. There were no differences in local wound complications.

CONCLUSIONS

The prone position has comparable complications to the supine position. With its benefits of increased oxygenation and decreased mortality, the prone position can be considered for trauma and surgical patients. A prospective multicenter study is warranted.

Effects of early versus delayed application of prone position on ventilation-perfusion mismatch in patients with acute respiratory distress syndrome: a prospective observational study

BACKGROUND

Prone position has been shown to improve oxygenation and survival in patients with early acute respiratory distress syndrome (ARDS). These beneficial effects are partly mediated by improved ventilation/perfusion (V/Q) distribution. Few studies have investigated the impact of early versus delayed proning on V/Q distribution in patients with ARDS. The aim of this study was to assess the regional ventilation and perfusion distribution in early versus persistent ARDS after prone position.

METHODS

This is a prospective, observational study from June 30, 2021, to October 1, 2022 at the medical ICU in Zhongda Hospital, Southeast University. Fifty-seven consecutive adult patients with moderate-to-severe ARDS ventilated in supine and prone position. Electrical impedance tomography was used to study V/Q distribution in the supine position and 12 h after a prone session.

RESULTS

Of the 57 patients, 33 were early ARDS (≤ 7 days) and 24 were persistent ARDS (> 7 days). Oxygenation significantly improved after proning in early ARDS (157 [121, 191] vs. 190 [164, 245] mm Hg, p < 0.001), whereas no significant change was found in persistent ARDS patients (168 [136, 232] vs.177 [155, 232] mm Hg, p = 0.10). Compared to supine position, prone reduced V/Q mismatch in early ARDS (28.7 [24.6, 35.4] vs. 22.8 [20.0, 26.8] %, p < 0.001), but increased V/Q mismatch in persistent ARDS (23.8 [19.8, 28.6] vs. 30.3 [24.5, 33.3] %, p = 0.006). In early ARDS, proning significantly reduced shunt in the dorsal region and dead space in the ventral region. In persistent ARDS, proning increased global shunt. A significant correlation was found between duration of ARDS onset to proning and the change in V/Q distribution (r = 0.54, p < 0.001).

CONCLUSIONS

Prone position significantly reduced V/Q mismatch in patients with early ARDS, while it increased V/Q mismatch in persistent ARDS patients. Trial registration ClinicalTrials.gov (NCT05207267, principal investigator Ling Liu, date of registration 2021.08.20).

Optimized ventilation power to avoid VILI

The effort to minimize VILI risk must be multi-pronged. The need to adequately ventilate, a key determinant of hazardous power, is reduced by judicious permissive hypercapnia, reduction of innate oxygen demand, and by prone body positioning that promotes both efficient pulmonary gas exchange and homogenous distributions of local stress. Modifiable ventilator-related determinants of lung protection include reductions of tidal volume, plateau pressure, driving pressure, PEEP, inspiratory flow amplitude and profile (using longer inspiration to expiration ratios), and ventilation frequency. Underappreciated conditional cofactors of importance to modulate the impact of local specific power may include lower vascular pressures and blood flows. Employed together, these measures modulate ventilation power with the intent to avoid VILI while achieving clinically acceptable targets for pulmonary gas exchange.

Incidence and Determinants of Acute Kidney Injury after Prone Positioning in Severe COVID-19 Acute Respiratory Distress Syndrome

(1) Background: Acute kidney injury (AKI) is common among critically ill COVID-19 patients, but its temporal association with prone positioning (PP) is still unknown, and no data exist on the possibility of predicting PP-associated AKI from bedside clinical variables. (2) Methods: We analyzed data from 93 COVID-19-related ARDS patients who underwent invasive mechanical ventilation (IMV) and at least one PP cycle. We collected hemodynamic variables, respiratory mechanics, and circulating biomarkers before, during, and after the first PP cycle. PP-associated AKI (PP-AKI) was defined as AKI diagnosed any time from the start of PP to 48 h after returning to the supine position. A t-test for independent samples was used to test for the differences between groups, while binomial logistical regression was performed to assess variables independently associated with PP-associated AKI. (3) Results: A total of 48/93 (52%) patients developed PP-AKI, with a median onset at 24 [13.5-44.5] hours after starting PP. No significant differences in demographic characteristics between groups were found. Before starting the first PP cycle, patients who developed PP-AKI had a significantly lower cumulative fluid balance (CFB), even when normalized for body weight (p = 0.006). Central venous pressure (CVP) values, measured before the first PP (OR 0.803, 95% CI [0.684-0.942], p = 0.007), as well as BMI (OR 1.153, 95% CI = [1.013-1.313], p = 0.031), were independently associated with the development of PP-AKI. In the multivariable regression analysis, a lower CVP before the first PP cycle was independently associated with ventilator-free days (OR 0.271, 95% CI [0.123-0.936], p = 0.011) and with ICU mortality (OR:0.831, 95% CI [0.699-0.989], p = 0.037). (4) Conclusions: Acute kidney injury occurs frequently in invasively ventilated severe COVID-19 ARDS patients undergoing their first prone positioning cycle. Higher BMI and lower CVP before PP are independently associated with the occurrence of AKI during prone positioning.

The physiological effect of prone positioning and lateral decubitus in non-intubated patients with severe COVID-19: a prospective cohort study

Introduction

Prone positioning is one type of postural lung recruitment manoeuvre that has been widely studied regarding the benefits and physiological changes of the cardiorespiratory system. However, prone positioning is not very comfortable for the patients because they have to lie on their stomachs for a while when the oxygen therapy and other monitoring devices are still attached. Based on patient observations, some patients will change to more comfortable positions, namely using the right/left lateral decubitus position. The purpose of this research was to examine the physiological impact of prone and lateral decubitus position in non-intubated patients who were diagnosed with severe COVID-19.

Methods

It was a prospective cohort study in subsequent people with severe COVID-19 who obtained a non-rebreathing mask or high-flow nasal cannula at a University Hospital between 1 June and 10 September 2021. The study lasted for a total of 2021 days and involved 48 patients. The patients assumed the prone positioning or lateral decubitus every morning and afternoon for 4 h and were measured for cardiorespiratory parameters and blood gas analysis. It has been reported in line with the STROCSS criteria.

Results

Dynamic changes based on cardiorespiratory parameters and blood gas analysis parameters in patients with prone and lateral decubitus position in patients with severe COVID-19 receiving conventional oxygen therapy (via non-rebreathing mask) or high-flow nasal cannula did not show any significant difference.

Conclusion

The physiological effect of prone positioning and lateral decubitus in non-intubated patients with severe COVID-19 are similar. Accordingly, lateral decubitus can be an alternative for postural lung recruitment manoeuvres and warrants further randomized trials.

Limitations of prone positioning in patients with aneurysmal subarachnoid hemorrhage and concomitant respiratory failure

OBJECTIVE

Prone positioning (PP) is an established treatment modality for respiratory failure. After aneurysmal subarachnoid hemorrhage (aSAH), PP is rarely performed considering the risk of intracranial hypertension. The aim of this study was to analyze the effects of PP on intracranial pressure (ICP), cerebral perfusion pressure (CPP) and cerebral oxygenation following aSAH.

PATIENTS AND METHODS

Demographic and clinical data of aSAH patients admitted over a 6-year period and treated with PP due to respiratory insufficiency were retrospectively analyzed. ICP, CPP, brain tissue oxygenation (pBrO2), respiratory parameters and ventilator settings were analyzed before and during PP.

RESULTS

Thirty patients receiving invasive multimodal neuromonitoring were included. Overall, 97 PP sessions were performed. Mean arterial oxygenation and pBrO2 increased significantly during PP. We found a significant increase in median ICP compared to the baseline level in supine position. No significant changes in CPP were observed. Five PP sessions had to be terminated early due to medically refractory ICP-crisis. The affected patients were younger (p = 0.02) with significantly higher baseline ICP values (p = 0.009). Baseline ICP correlates significantly (p < 0.001) with ICP 1 h (R: 0.57) and 4 h (R: 0.55) after onset of PP.

CONCLUSION

PP in aSAH patients with respiratory insufficiency is an effective therapeutic option improving arterial and global cerebral oxygenation without compromising CPP. The significant increase in ICP was moderate in most sessions. However, as some patients experience intolerable ICP crises during PP, continuous ICP-Monitoring is considered mandatory. Patients with elevated baseline ICP and reduced intracranial compliance should not be considered for PP.

Cardiac dysfunction in severe pediatric acute respiratory distress syndrome: the right ventricle in search of the right therapy

Severe acute respiratory distress syndrome in children, or PARDS, carries a high risk of morbidity and mortality that is not fully explained by PARDS severity alone. Right ventricular (RV) dysfunction can be an insidious and often under-recognized complication of severe PARDS that may contribute to its untoward outcomes. Indeed, recent evidence suggest significantly worse outcomes in children who develop RV failure in their course of PARDS. However, in this narrative review, we highlight the dearth of evidence regarding the incidence of and risk factors for PARDS-associated RV dysfunction. While we wish to draw attention to the absence of available evidence that would inform recommendations around surveillance and treatment of RV dysfunction during severe PARDS, we leverage available evidence to glean insights into potentially helpful surveillance strategies and therapeutic approaches.

A framework for heart-lung interaction and its application to prone position in the acute respiratory distress syndrome

While both cardiac output (Qcirculatory) and right atrial pressure (PRA) are important measures in the intensive care unit (ICU), they are outputs of the system and not determinants. That is to say, in a model of the circulation wherein venous return and cardiac function find equilibrium at an 'operating point' (OP, defined by the PRA on the x-axis and Qcirculatory on the y-axis) both the PRA and Qcirculatory are, necessarily, dependent variables. A simplified geometrical approximation of Guyton's model is put forth to illustrate that the independent variables of the system are: 1) the mean systemic filling pressure (PMSF), 2) the pressure within the pericardium (PPC), 3) cardiac function and 4) the resistance to venous return. Classifying independent and dependent variables is clinically-important for therapeutic control of the circulation. Recent investigations in patients with acute respiratory distress syndrome (ARDS) have illuminated how PMSF, cardiac function and the resistance to venous return change when placing a patient in prone. Moreover, the location of the OP at baseline and the intimate physiological link between the heart and the lungs also mediate how the PRA and Qcirculatory respond to prone position. Whereas turning a patient from supine to prone is the focus of this discussion, the principles described within the framework apply equally-well to other more common ICU interventions including, but not limited to, ventilator management, initiating vasoactive medications and providing intravenous fluids.

Extended prone positioning for intubated ARDS: a review

During the COVID-19 pandemic, several centers had independently reported extending prone positioning beyond 24 h. Most of these centers reported maintaining patients in prone position until significant clinical improvement was achieved. One center reported extending prone positioning for organizational reasons relying on a predetermined fixed duration. A recent study argued that a clinically driven extension of prone positioning beyond 24 h could be associated with reduced mortality. On a patient level, the main benefit of extending prone positioning beyond 24 h is to maintain a more homogenous distribution of the gas-tissue ratio, thus delaying the increase in overdistention observed when patients are returned to the supine position. On an organizational level, extending prone positioning reduces the workload for both doctors and nurses, which might significantly enhance the quality of care in an epidemic. It might also reduce the incidence of accidental catheter and tracheal tube removal, thereby convincing intensive care units with low incidence of ARDS to prone patients more systematically. The main risk associated with extended prone positioning is an increased incidence of pressure injuries. Up until now, retrospective studies are reassuring, but prospective evaluation is needed.

Awake prone positioning in acute hypoxaemic respiratory failure

Awake prone positioning (APP) of patients with acute hypoxaemic respiratory failure gained considerable attention during the early phases of the coronavirus disease 2019 (COVID-19) pandemic. Prior to the pandemic, reports of APP were limited to case series in patients with influenza and in immunocompromised patients, with encouraging results in terms of tolerance and oxygenation improvement. Prone positioning of awake patients with acute hypoxaemic respiratory failure appears to result in many of the same physiological changes improving oxygenation seen in invasively ventilated patients with moderate-severe acute respiratory distress syndrome. A number of randomised controlled studies published on patients with varying severity of COVID-19 have reported apparently contrasting outcomes. However, there is consistent evidence that more hypoxaemic patients requiring advanced respiratory support, who are managed in higher care environments and who can be prone for several hours, benefit most from APP use. We review the physiological basis by which prone positioning results in changes in lung mechanics and gas exchange and summarise the latest evidence base for APP primarily in COVID-19. We examine the key factors that influence the success of APP, the optimal target populations for APP and the key unknowns that will shape future research.

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 .

Right ventricle-specific therapies in acute respiratory distress syndrome: a scoping review

OBJECTIVE

To summarize knowledge and identify gaps in evidence regarding treatment of right ventricular dysfunction (RVD) in acute respiratory distress syndrome (ARDS).

DATA SOURCES

We conducted a comprehensive search of MEDLINE, Embase, CINAHL, Web of Science, and the Cochrane Central Register of Controlled Trials.

STUDY SELECTION

Studies were included if they reported effects of treatments on right ventricular function, whether or not the intent was to modify right ventricular function.

DATA EXTRACTION

Data extraction was performed independently and in duplicate by two authors. Data items included the study design, patient population, type of intervention, comparison group, and RV-specific outcomes.

DATA SYNTHESIS

Of 1,430 studies screened, 51 studies reporting on 1,526 patients were included. By frequency, the included studies examined the following interventions: ventilator settings (29.4%), inhaled medications (33.3%), extracorporeal life support (13.7%), intravenous or oral medications (13.7%), and prone positioning (9.8%). The majority of the studies were non-randomized experimental studies (53%), with the next most common being case reports (16%). Only 5.9% of studies were RCTs. In total, 27% of studies were conducted with the goal of modifying RV function.

CONCLUSIONS

Given the prevalence of RVD in ARDS and its association with mortality, the dearth of research on this topic is concerning. This review highlights the need for prospective trials aimed at treating RV dysfunction in ARDS.

Individualizing Fluid Management in Patients with Acute Respiratory Distress Syndrome and with Reduced Lung Tissue Due to Surgery—A Narrative Review

Fluids are the cornerstone of therapy in all critically ill patients. During the last decades, we have made many steps to get fluid therapy personalized and based on individual needs. In patients with lung involvement—acute respiratory distress syndrome—finding the right amount of fluids after lung surgery may be extremely important because lung tissue is one of the most vulnerable to fluid accumulation. In the current narrative review, we focus on the actual perspectives of fluid therapy with the aim of showing the possibilities to tailor the treatment to a patient’s individual needs using fluid responsiveness parameters and other therapeutic modalities.

Dead space ventilation-related indices: bedside tools to evaluate the ventilation and perfusion relationship in patients with acute respiratory distress syndrome

Cumulative evidence has demonstrated that the ventilatory ratio closely correlates with mortality in acute respiratory distress syndrome (ARDS), and a primary feature in coronavirus disease 2019 (COVID-19)-ARDS is increased dead space that has been reported recently. Thus, new attention has been given to this group of dead space ventilation-related indices, such as physiological dead space fraction, ventilatory ratio, and end-tidal-to-arterial PCO₂ ratio, which, albeit distinctive, are all global indices with which to assess the relationship between ventilation and perfusion. These parameters have already been applied to positive end expiratory pressure titration, prediction of responses to the prone position and the field of extracorporeal life support for patients suffering from ARDS. Dead space ventilation-related indices remain hampered by several deflects; notwithstanding, for this catastrophic syndrome, they may facilitate better stratifications and identifications of subphenotypes, thereby providing therapy tailored to individual needs.

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.

Functioning of the Human Heart in the Pron-Position

Aim      To study intracardiac hemodynamics in healthy men in supine and prone positions.Material and methods  This echocardiography study included 14 apparently healthy men at a mean age of 38 years.Results In a prone position, the heart configuration and location in the chest changed, the heart rate increased by 7.3 %, and the transaortic flow velocity decreased by 13.7 %. Also, early and late right ventricular diastolic filling velocities and the pulmonary artery flow velocity were increased by 31.7, 11.4, and 5.6 %, respectively. In the intact tricuspid valve, the velocity and regurgitation pressure gradient were reduced by 7 % and 14.2 %, respectively.Conclusion      In a prone position, spatial changes in the location of the heart and its structures influence velocities of intracardiac blood flow, which may initiate the development of heart failure if the prone position is long-lasting.

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

Early Awake Prone Position Combined with High-Flow Nasal Oxygen Therapy in Severe COVID-19: A Case Series

Background

Awake prone positioning has been used for non-intubated patients with COVID-19-related acute hypoxaemic respiratory failure, but the results are contradictory. We aimed to highlight the role of awake prone positioning combined with high-flow nasal oxygen therapy in severe COVID-19 patients infected with the Delta variant of SARS-CoV-2.

Methods

From June 12 to December 7, 2021, we successfully performed prone position(PP) combined with high-flow nasal oxygen(HFNO) therapy on two patients infected with the delta variant of SARS-CoV-2. HFNO was prescribed to reach SpO₂ ≥ 92%. PP was proposed to patients with PaO₂/FiO₂(P/F) < 150 mmHg. Arterial blood gas (ABG) and hemodynamic were monitored before and after PP sessions. The target time of PP was more than 12 h per day and could be appropriately shortened according to the patient's tolerance. Relevant clinical data, HFNO parameters, PICCO parameters, P/F ratio and PP duration were obtained from medical records.

Results

A total of 23 PP sessions and 6 PP sessions combined with HFNO were performed in case 1 and case 2, respectively. Compared with values before PP, GEDI, ELWI and Qs/Qt decreased significantly (GEDI: 869.50 ± 60.50 ml/m² vs. 756.86 ± 88.25 ml/m²; ELWI: 13.64 ± 2.82 ml/kg vs. 12.43 ± 2.50 ml/kg; Qs/Qt: 15.32 ± 6.52% vs. 12.24 ± 5.39%; all p < 0.05), Meanwhile, the oxygenation improved significantly (P/F: 184.50 ± 51.92 mmHg vs. 234.21 ± 88.84 mmHg, p < 0.05), The chest CT revealed the lung infiltrates improved significantly after PP. Both cases were discharged to a dedicated COVID-19 ward without requiring intubation.

Conclusions

Combining PP with HFNO could be a useful treatment strategy for avoiding intubation in severe COVID-19 patients infected with the Delta variant of SARS-CoV-2 to improve pulmonary vascular involvement, improve oxygenation and avoid intubation, but further studies are needed to validate our approach.

Prone positioning in ARDS patients supported with VV ECMO, what we should explore?

Background

Acute respiratory distress syndrome (ARDS), a prevalent cause of admittance to intensive care units, is associated with high mortality. Prone positioning has been proven to improve the outcomes of moderate to severe ARDS patients owing to its physiological effects. Venovenous extracorporeal membrane oxygenation (VV ECMO) will be considered in patients with severe hypoxemia. However, for patients with severe hypoxemia supported with VV ECMO, the potential effects and optimal strategies of prone positioning remain unclear. This review aimed to present these controversial questions and highlight directions for future research.

Main body

The clinically significant benefit of prone positioning and early VV ECMO alone was confirmed in patients with severe ARDS. However, a number of questions regarding the combination of VV ECMO and prone positioning remain unanswered. We discussed the potential effects of prone positioning on gas exchange, respiratory mechanics, hemodynamics, and outcomes. Strategies to achieve optimal outcomes, including indications, timing, duration, and frequency of prone positioning, as well as the management of respiratory drive during prone positioning sessions in ARDS patients receiving VV ECMO, are challenging and controversial. Additionally, whether and how to implement prone positioning according to ARDS phenotypes should be evaluated. Lung morphology monitored by computed tomography, lung ultrasound, or electrical impedance tomography might be a potential indication to make an individualized plan for prone positioning therapy in patients supported with VV ECMO.

Conclusion

For patients with ARDS supported with VV ECMO, the potential effects of prone positioning have yet to be clarified. Ensuring an optimal strategy, especially an individualized plan for prone positioning therapy during VV ECMO, is particularly challenging and requires further research.

Prone positioning may increase lung overdistension in COVID-19-induced ARDS

Real-time effects of changing body position and positive end-expiratory pressure (PEEP) on regional lung overdistension and collapse in individual patients remain largely unknown and not timely monitored. The aim of this study was to individualize PEEP in supine and prone body positions seeking to reduce lung collapse and overdistension in mechanically ventilated patients with coronavirus disease (COVID-19)-induced acute respiratory distress syndrome (ARDS). We hypothesized that prone positioning with bedside titrated PEEP would provide attenuation of both overdistension and collapse. In this prospective observational study, patients with COVID-19-induced ARDS under mechanical ventilation were included. We used electrical impedance tomography (EIT) with decremental PEEP titration algorithm (PEEP_{EIT-titration}), which provides information on regional lung overdistension and collapse, along with global respiratory system compliance, to individualize PEEP and body position. PEEP_{EIT-titration} in supine position followed by PEEP_{EIT-titration} in prone position were performed. Immediately before each PEEP_{EIT-titration}, the same lung recruitment maneuver was performed: 2 min of PEEP 24 cmH₂O and driving pressure of 15 cmH₂O. Forty-two PEEP_{EIT-titration} were performed in ten patients (21 pairs supine and prone positions). We have found larger % of overdistension along the PEEP titration in prone than supine position (P = 0.042). A larger % of collapse along the PEEP titration was found in supine than prone position (P = 0.037). A smaller respiratory system compliance was found in prone than supine position (P < 0.0005). In patients with COVID-19-induced ARDS, prone body position, when compared with supine body position, decreased lung collapse at low PEEP levels, but increased lung overdistension at PEEP levels greater than 10 cm H₂O.

Trial registration number: NCT04460859.

The Association of Proning and Stroke among Deeply Sedated Critically Ill SARS-CoV-2 (COVID-19) Patients

There has been an increasing incidence of stroke cases among SARS-CoV-2 (COVID-19) patients who were deeply sedated and underwent proning positioning. We reviewed the association of proning and sedations used to the development of stroke, including demographic profiles of patients with COVID-19 infection in the critical care unit. There was a significant association seen among COVID-19 patients in the ICU who underwent proning to the development of stroke, with up to 15 times risk of having stroke (p value = 0.007) than those who were not proned during their course of ICU stay. Patients who were given propofol and fentanyl as sedation during proning for more than 24 hours was significantly associated with the development of stroke (p value = 0.004). Patient risk factors were also studied (age variability, hypertension, diabetes, smoking, and alcoholism) and showed that patients who were alcoholic beverage drinkers were significantly associated to the development of stroke during proning (p value = <0.001). The usual risk factors for stroke in the general population (hypertension, diabetes, and cigarette smoking) were not associated with stroke development during proning, strengthening the fact that proning during COVID-19 infection is an independent risk factor for the development of stroke thus needing stroke surveillance during the duration of proning.

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.

Venous return and mean systemic filling pressure: physiology and clinical applications

Venous return is the flow of blood from the systemic venous network towards the right heart. At steady state, venous return equals cardiac output, as the venous and arterial systems operate in series. However, unlike the arterial one, the venous network is a capacitive system with a high compliance. It includes a part of unstressed blood, which is a reservoir that can be recruited via sympathetic endogenous or exogenous stimulation. Guyton’s model describes the three determinants of venous return: the mean systemic filling pressure, the right atrial pressure and the resistance to venous return. Recently, new methods have been developed to explore such determinants at the bedside. In this narrative review, after a reminder about Guyton’s model and current methods used to investigate it, we emphasize how Guyton’s physiology helps understand the effects on cardiac output of common treatments used in critically ill patients.

Early prolonged prone position in noninvasively ventilated patients with SARS-CoV-2-related moderate-to-severe hypoxemic respiratory failure: clinical outcomes and mechanisms for treatment response in the PRO-NIV study

Background

Whether prone position (PP) improves clinical outcomes in COVID-19 pneumonia treated with noninvasive ventilation (NIV) is unknown. We evaluated the effect of early PP on 28-day NIV failure, intubation and death in noninvasively ventilated patients with moderate-to-severe acute hypoxemic respiratory failure due to COVID-19 pneumonia and explored physiological mechanisms underlying treatment response.

Methods

In this controlled non-randomized trial, 81 consecutive prospectively enrolled patients with COVID-19 pneumonia and moderate-to-severe (paO2/FiO2 ratio < 200) acute hypoxemic respiratory failure treated with early PP + NIV during Dec 2020–May 2021were compared with 162 consecutive patients with COVID-19 pneumonia matched for age, mortality risk, severity of illness and paO2/FiO2 ratio at admission, treated with conventional (supine) NIV during Apr 2020–Dec 2020 at HUMANITAS Gradenigo Subintensive Care Unit, after propensity score adjustment for multiple baseline and treatment-related variables to limit confounding. Lung ultrasonography (LUS) was performed at baseline and at day 5. Ventilatory parameters, physiological dead space indices (DSIs) and circulating inflammatory and procoagulative biomarkers were monitored during the initial 7 days.

Results

In the intention-to-treat analysis. NIV failure occurred in 14 (17%) of PP patients versus 70 (43%) of controls [HR = 0.32, 95% CI 0.21–0.50; p < 0.0001]; intubation in 8 (11%) of PP patients versus 44 (30%) of controls [HR = 0.31, 95% CI 0.18–0.55; p = 0.0012], death in 10 (12%) of PP patients versus 59 (36%) of controls [HR = 0.27, 95% CI 0.17–0.44; p < 0.0001]. The effect remained significant within different categories of severity of hypoxemia (paO2/FiO2 < 100 or paO2/FiO2 100–199 at admission). Adverse events were rare and evenly distributed. Compared with controls, PP therapy was associated with improved oxygenation and DSIs, reduced global LUS severity indices largely through enhanced reaeration of dorso-lateral lung regions, and an earlier decline in inflammatory markers and D-dimer. In multivariate analysis, day 1 CO2 response outperformed O2 response as a predictor of LUS changes, NIV failure, intubation and death.

Conclusion

Early prolonged PP is safe and is associated with lower NIV failure, intubation and death rates in noninvasively ventilated patients with COVID-19-related moderate-to-severe hypoxemic respiratory failure. Early dead space reduction and reaeration of dorso-lateral lung regions predicted clinical outcomes in our study population.

Clinical trial registration

ISRCTN23016116. Retrospectively registered on May 1, 2021.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13054-022-03937-x.

Respiratory-Cardiovascular Interactions During Mechanical Ventilation: Physiology and Clinical Implications

Positive-pressure inspiration and positive end-expiratory pressure (PEEP) increase pleural, alveolar, lung transmural, and intra-abdominal pressure, which decrease right and left ventricular (RV; LV) preload and LV afterload and increase RV afterload. The magnitude and clinical significance of the resulting changes in ventricular function are determined by the delivered tidal volume, the total level of PEEP, the compliance of the lungs and chest wall, intravascular volume, baseline RV and LV function, and intra-abdominal pressure. In mechanically ventilated patients, the most important, adverse consequences of respiratory-cardiovascular interactions are a PEEP-induced reduction in cardiac output, systemic oxygen delivery, and blood pressure; RV dysfunction in patients with ARDS; and acute hemodynamic collapse in patients with pulmonary hypertension. On the other hand, the hemodynamic changes produced by respiratory-cardiovascular interactions can be beneficial when used to assess volume responsiveness in hypotensive patients and by reducing dyspnea and improving hypoxemia in patients with cardiogenic pulmonary edema. Thus, a thorough understanding of the physiological principles underlying respiratory-cardiovascular interactions is essential if critical care practitioners are to anticipate, recognize, manage, and utilize their hemodynamic effects. © 2022 American Physiological Society. Compr Physiol 12:1-24, 2022.

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.

Early prone positioning in acute respiratory distress syndrome related to COVID-19: a propensity score analysis from the multicentric cohort COVID-ICU network-the ProneCOVID study

Background

Delaying time to prone positioning (PP) may be associated with higher mortality in acute respiratory distress syndrome (ARDS) due to coronavirus disease 2019 (COVID-19). We evaluated the use and the impact of early PP on clinical outcomes in intubated patients hospitalized in intensive care units (ICUs) for COVID-19.

Methods

All intubated patients with ARDS due to COVID-19 were involved in a secondary analysis from a prospective multicenter cohort study of COVID-ICU network including 149 ICUs across France, Belgium and Switzerland. Patients were followed-up until Day-90. The primary outcome was survival at Day-60. Analysis used a Cox proportional hazard model including a propensity score.

Results

Among 2137 intubated patients, 1504 (70.4%) were placed in PP during their ICU stay and 491 (23%) during the first 24 h following ICU admission. One hundred and eighty-one patients (36.9%) of the early PP group had a PaO₂/FiO₂ ratio > 150 mmHg when prone positioning was initiated. Among non-early PP group patients, 1013 (47.4%) patients had finally been placed in PP within a median delay of 3 days after ICU admission. Day-60 mortality in non-early PP group was 34.2% versus 39.3% in the early PP group (p = 0.038). Day-28 and Day-90 mortality as well as the need for adjunctive therapies was more important in patients with early PP. After propensity score adjustment, no significant difference in survival at Day-60 was found between the two study groups (HR 1.34 [0.96–1.68], p = 0.09 and HR 1.19 [0.998–1.412], p = 0.053 in complete case analysis or in multiple imputation analysis, respectively).

Conclusions

In a large multicentric international cohort of intubated ICU patients with ARDS due to COVID-19, PP has been used frequently as a main treatment. In this study, our data failed to show a survival benefit associated with early PP started within 24 h after ICU admission compared to PP after day-1 for all COVID-19 patients requiring invasive mechanical ventilation regardless of their severity.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13054-022-03949-7.

Application of POCUS in patients with COVID-19 for acute respiratory distress syndrome management: a narrative review

COVID-19 has inflicted the world for over two years. The recent mutant virus strains pose greater challenges to disease prevention and treatment. COVID-19 can cause acute respiratory distress syndrome (ARDS) and extrapulmonary injury. Dynamic monitoring of each patient's condition is necessary to timely tailor treatments, improve prognosis and reduce mortality. Point-of-care ultrasound (POCUS) is broadly used in patients with ARDS. POCUS is recommended to be performed regularly in COVID-19 patients for respiratory failure management. In this review, we summarized the ultrasound characteristics of COVID-19 patients, mainly focusing on lung ultrasound and echocardiography. Furthermore, we also provided the experience of using POCUS to manage COVID-19-related ARDS.

Approach to echocardiography in ARDS patients in the prone position: A systematic review

Echocardiography is commonly utilized in patients with acute respiratory distress syndrome (ARDS) for assessment of cardiac function, volume status, and the potential development of acute cor pulmonale. In severe ARDS, prone positioning is frequently used, which imposes technical challenges during transthoracic echocardiography (TTE) image acquisition. Moreover, prone positioning can affect cardiopulmonary function in ways that are reflected on the echocardiographic findings in this position. Historically, a transesophageal approach was recommended when a patient is prone, with few studies reporting utility of TTE in this setting. However, recent publications have begun to address this knowledge gap. This review explores recent literature addressing the use of TTE in prone patients with ARDS, with a special focus on the cardiopulmonary effects of proning and potential solutions to the technical difficulties that arise in this position.