Clinical features and respiratory pathophysiology of COVID-19 patients ventilated in the prone position: a cohort study

Introduction
There are few studies that have investigated the response to the prone position in mechanically ventilated COVID-19 patients with acute respiratory distress syndrome (ARDS). We describe the characteristics and outcomes of those patients in a tertiary hospital in Spain.

Material and methods
This is an observational study in consecutive, mechanically ventilated COVID-19 patients. The primary endpoint was to describe the respiratory pathophysio­logy and clinical outcomes of COVID-19 patients treated by mechanical ventilation in the prone position.

Results
Of 84 patients mechanically ventilated in the prone position, 19 (22%) were successfully extubated and 43 (51%) were discharged from the ICU. The duration of mechanical ventilation and ICU length of stay were 11 days (IQR 8–16) and 15 days (IQR 9–25), respectively. On admission to ICU, 61% patients had a moderate ARDS according to the Berlin criteria. 76% had 4 lung quadrants affected. After intubation, the median PaO2/FiO2 was 105 (IQR 76–138), ventilatory ratio was 1.48 (IQR 1.16–1.88), and compliance was 33 mL cm H2O–1 (IQR 25–41). The median number of cycles in the prone position was 2 (1–3), with a median of total hours in the prone position of 76 (IQR 64–111). 72 h after the first prone position cycle the median PaO2/FiO2 increase was up to 193 (IQR 152–251), but the compliance was similar to the basal level (34 mL cm H2O–1 [IQR 26–43]). However, the percentage of patients with normal compliance (> 50 mL cm H2O–1) increased with the prone position from 15% (n = 13) to 32% (n = 27) after 72 h.

Conclusions
In our study, the COVID-19 patients with respiratory failure presented respiratory mechanics, gas exchange parameters, and a response to prone ventilation similar to those observed in other causes of ARDS.