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

Abstract

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.

Figure 1

Lung overdistension by electrical impedance tomography in supine vs. prone body position. Line graphs of the electrical impedance tomography (EIT)-based estimations of lung overdistension from forty-two decremental positive end-expiratory pressure (PEEP) titrations—supine vs. prone body position—are shown (mean ± SEM). Some illustrative EIT images of overdistension from one mechanically ventilated patient with coronavirus disease (COVID-19)-induced acute respiratory distress syndrome (ARDS) are also shown: overdistended pixels in white. Note that prone body position increased lung overdistension in comparison with the supine one. Triangle up (white): supine body position. Triangle down (black): prone body position. X axis: decremental PEEP levels of the EIT-PEEP titrations. Y axis: percent of overdistended lung units out of the total lung imaged by EIT.

Figure 2

Lung collapse by electrical impedance tomography in supine vs. prone body position. Line graphs of the electrical impedance tomography (EIT)-based estimations of lung collapse from forty-two decremental positive end-expiratory pressure (PEEP) titrations—supine vs. prone body position—are shown (mean ± SEM). Triangle up (white): supine body position. Triangle down (black): prone body position. X axis: decremental PEEP levels of the EIT-PEEP titrations. Y axis: percent of collapsed lung units out of the total lung imaged by EIT.

Figure 3

Respiratory system compliance in supine vs. prone body position. Line graphs of the respiratory system compliance from forty-two decremental positive end-expiratory pressure (PEEP) titrations—supine vs. prone body position—are shown (mean ± SEM). Triangle up (white): supine body position. Triangle down (black): prone body position. X axis: decremental PEEP levels of the EIT-PEEP titrations. Y axis: respiratory system compliance.