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

Pathophysiological Markers of Acute Respiratory Distress Syndrome Severity Are Correlated With Ventilation-Perfusion Mismatch Measured by Electrical Impedance Tomography

OBJECTIVES

Pulmonary ventilation/perfusion (V/Q) mismatch measured by electrical impedance tomography (EIT) is associated with the outcome of patients with the acute respiratory distress syndrome (ARDS), but the underlying pathophysiological mechanisms have not been fully elucidated. The present study aimed to verify the correlation between relevant pathophysiological markers of ARDS severity and V/Q mismatch.

DESIGN

Prospective observational study.

SETTING

General ICU of a university-affiliated hospital.

PATIENTS

Deeply sedated intubated adult patients with ARDS under controlled mechanical ventilation.

INTERVENTIONS

Measures of V/Q mismatch by EIT, respiratory mechanics, gas exchange, lung imaging, and plasma biomarkers.

MEASUREMENTS AND MAIN RESULTS

Unmatched V/Q units were assessed by EIT as the fraction of ventilated nonperfused plus perfused nonventilated lung units. At the same time, plasma biomarkers with proven prognostic and mechanistic significance for ARDS (carbonic anhydrase 9 [CA9], hypoxia-inducible factor 1 [HIF1], receptor for advanced glycation endproducts [RAGE], angiopoietin 2 [ANG2], gas exchange, respiratory mechanics, and quantitative chest CT scans were measured. Twenty-five intubated ARDS patients were included with median unmatched V/Q units of 37.1% (29.2-49.2%). Unmatched V/Q units were correlated with plasma levels of CA9 (rho = 0.47; p = 0.01), HIF1 (rho = 0.40; p = 0.05), RAGE (rho = 0.46; p = 0.02), and ANG2 (rho = 0.42; p = 0.03). Additionally, unmatched V/Q units correlated with plateau pressure (r = 0.38; p = 0.05) and with the number of quadrants involved on chest radiograph (r = 0.73; p < 0.01). Regional unmatched V/Q units were correlated with the corresponding fraction of poorly aerated lung tissue (r = 0.62; p = 0.01) and of lung tissue weight (rho: 0.51; p = 0.04) measured by CT scan.

CONCLUSIONS

In ARDS patients, unmatched V/Q units are correlated with pathophysiological markers of lung epithelial and endothelial dysfunction, increased lung stress, and lung edema. Unmatched V/Q units could represent a comprehensive marker of ARDS severity, reflecting the complex organ pathophysiology and reinforcing their prognostic significance.

Extended versus Standard Proning Duration for COVID-19-associated Acute Respiratory Distress Syndrome: A Target Trial Emulation Study

Rationale: Prone positioning for ⩾16 hours in moderate-to-severe acute respiratory distress syndrome (ARDS) improves survival. However, the optimal duration of proning is unknown. Objectives: To estimate the effect of extended versus standard proning duration on patients with moderate-to-severe coronavirus disease (COVID-19) ARDS. Methods: Data were extracted from a five-hospital electronic medical record registry. Patients who were proned within 72 hours of mechanical ventilation were categorized as receiving extended (⩾24 h) versus standard (16-24 h) proning based on the first proning session length. We used a target trial emulation design to estimate the effect of extended versus standard proning on the primary outcome of 90-day mortality and secondary outcomes of ventilator liberation and intensive care unit (ICU) discharge. Analytically, we used inverse probability of treatment weighted (IPTW) Cox or Fine-Gray regression models. Results: A total of 314 patients were included; 234 received extended proning, and 80 received standard-duration proning. Patients who received extended proning were older, had greater comorbidity, were more often at an academic hospital, and had shorter time from admission to mechanical ventilation. After IPTW, characteristics were well balanced. Unadjusted 90-day mortality in the extended versus standard proning groups was 39% versus 58%. In doubly robust IPTW analyses, we found no significant effects of extended versus standard proning duration on mortality (hazard ratio [95% confidence interval], 0.95 [0.51-1.77]), ventilator liberation (subdistribution hazard, 1.60 [0.97-2.64], or ICU discharge (subdistribution hazard, 1.31 [0.82-2.10]). Conclusions: Using target trial emulation, we found no significant effect of extended versus standard proning duration on mortality, ventilator liberation, or ICU discharge. However, given the imprecision of estimates, further study is justified.

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.