Physiologic Effects of the Awake Prone Position Combined With High-Flow Nasal Oxygen on Gas Exchange and Work of Breathing in Patients With Severe COVID-19 Pneumonia: A Randomized Crossover Trial

Abstract

To determine the effect of the awake prone position (APP) on gas exchange and the work of breathing in spontaneously breathing patients with COVID-19-associated acute hypoxemic respiratory failure (AHRF) supported by high-flow nasal oxygen.

Design: Prospective randomized physiologic crossover multicenter trial.

Settings: Four ICUs in Marseille, France.

Patients: Seventeen patients with laboratory-confirmed COVID-19 pneumonia and Pao₂/Fio₂ less than or equal to 300 mm Hg while treated with high-flow nasal cannula oxygen therapy.

Interventions: Periods of APP and semirecumbent position (SRP) were randomly applied for 2 hours and separated by a 2-hour washout period.

Measurements and main results: Arterial blood gases, end-tidal CO₂. and esophageal pressure were recorded prior to and at the end of each period. Inspiratory muscle effort was assessed by measuring the esophageal pressure swing (∆P_ES) and the simplified esophageal pressure-time product (sPTP_ES). The other endpoints included physiologic dead space to tidal volume ratio (V_D/V_T) and the transpulmonary pressure swing. The APP increased the Pao₂/Fio₂ from 84 Torr (61-137 Torr) to 208 Torr (114-226 Torr) (p = 0.0007) and decreased both the V_D/V_T and the respiratory rate from 0.54 (0.47-0.57) to 0.49 (0.45-0.53) (p = 0.012) and from 26 breaths/min (21-30 breaths/min) to 21 breaths/min (19-22 breaths/min), respectively (p = 0.002). These variables remained unchanged during the SRP. The ∆P_ES and sPTP_ES per breath were unaffected by the position. However, the APP reduced the sPTP_ES per minute from 225 cm H₂O.s.m^-1 (176-332 cm H₂O.s.m^-1) to 174 cm H₂O.s.m^-1 (161-254 cm H₂O.s.m^-1) (p = 0.049).

Conclusions: In spontaneously breathing patients with COVID-19-associated AHRF supported by high-flow nasal oxygen, the APP improves oxygenation and reduces the physiologic dead space, respiratory rate, and work of breathing per minute.

Keywords: COVID-19; prone position; respiratory distress syndrome; respiratory insufficiency; work of breathing.

Figure 1.

Effects of the semirecumbent position (SRP) and prone position (PP) on the Pao₂/Fio₂ ratio. A, Dot plots and lines of Pao₂/Fio₂ at baseline and the end (120 min) of each period during the SRP and PP. The horizontal line indicates the median value. B, Dot plots and lines of the relative variation in Pao₂/Fio₂ during the SRP and PP, which was computed as 100 × (end value–baseline value)/baseline value. The baseline of each period was normalized to the reference level (zero). The horizontal line indicates the median value. C, Dot plots of the absolute variation in Pao₂/Fio₂ during the PP in the responders and nonresponders, which was computed as the end value–baseline value. The horizontal lines indicate the median values and the 25–75th percentiles. Among the six nonresponders, three had a ∆Pao₂/Fio₂ greater than 20 mm Hg.

Figure 2.

Effects of the semirecumbent position (SRP) and prone position (PP) on the physiologic dead space to tidal volume ratio (V_D/V_T). A, Dot plots and lines of V_D/V_T at baseline and the end (120 min) of each period during the SRP and PP. The horizontal line indicates the median value. B, Dot plots and lines of the relative variation in V_D/V_T during the SRP and PP, which was computed as 100 × (end value–baseline value)/baseline value. The baseline of each period was normalized to the reference level (zero). The horizontal line indicates the median value. C, Scatter plot and regression analysis of the relative variation in V_D/V_T and the relative variation in Pao₂/Fio₂. The dashed lines indicate the 95% CI of the regression line.

Figure 3.

Effects of the semirecumbent position (SRP) and prone position (PP) on the respiratory rate (RR). A, Dot plots and lines of the RR at the baseline and the end (120 min) of each period during the SRP and PP. The horizontal line indicates the median value. B, Dot plots and lines of the relative variation in the RR during the SRP and PP, which was computed as 100 × (end value–baseline value)/baseline value. The baseline of each period was normalized to the reference level (zero). The horizontal line indicates the median value. C, Scatter plot and regression analysis of the relative variation in the RR and the relative variation in Pao₂/Fio₂. The dashed lines indicate the 95% CI of the regression line.

Figure 4.

Effects of the semirecumbent position (SRP) and prone position (PP) on inspiratory muscle effort. A, Dot plots and lines of the relative variation in the esophageal pressure swing (∆P_ES) during SRP and PP, which was computed as 100 × (end value–baseline value)/baseline value. The baseline of each period was normalized to the reference level (zero). The horizontal line indicates the median value. B, Scatter plot and regression analysis of the baseline ∆P_ES and the relative variation in ∆P_ES during the PP. The dashed lines indicate the 95% CI of the regression line. C, Dot plots and lines of the relative variation in the simplified esophageal pressure–time product per minute (sPTP_min) during the SRP and PP, which was computed as 100 × (end value–baseline value)/baseline value. The baseline of each period was normalized to the reference level (zero). The horizontal line indicates the median value. D, Scatter plot and regression analysis of the baseline sPTP_min and the relative variation in sPTP_min during the PP. The dashed lines indicate the 95% CI of the regression line.