Low PEEP Mechanical Ventilation and PaO2/FiO2 Ratio Evolution in COVID-19 Patients

Abstract

Invasive mechanical ventilation (IMV) is the standard treatment in critically ill COVID-19 patients with acute severe respiratory distress syndrome (ARDS). When IMV setting is extremely aggressive, especially through the application of high positive-end-expiratory respiration (PEEP) values, lung damage can occur. Until today, in COVID-19 patients, two types of ARDS were identified (L- and H-type); for the L-type, a lower PEEP strategy was supposed to be preferred, but data are still missing. The aim of this study was to evaluate if a clinical management with lower PEEP values in critically ill L-type COVID-19 patients was safe and efficient in comparison to usual standard of care. A retrospective analysis was conducted on consecutive patients with COVID-19 ARDS admitted to the ICU and treated with IMV. Patients were treated with a lower PEEP strategy adapted to BMI: PEEP 10 cmH₂O if BMI < 30 kg m^-2, PEEP 12 cmH₂O if BMI 30-50 kg m^-2, PEEP 15 cmH₂O if BMI > 50 kg m^-2. Primary endpoint was the PaO₂/FiO₂ ratio evolution during the first 3 IMV days; secondary endpoints were to analyze ICU length of stay (LOS) and IMV length. From March 2 to January 15, 2021, 79 patients underwent IMV. Average applied PEEP was 11 ± 2.9 cmH₂O for BMI < 30 kg m^-2 and 16 ± 3.18 cmH₂O for BMI > 30 kg m^-2. During the first 24 h of IMV, patients' PaO₂/FiO₂ ratio presented an improvement (p<0.001; CI 99%) that continued daily up to 72 h (p<0.001; CI 99%). Median ICU LOS was 15 days (10-28); median duration of IMV was 12 days (8-26). The ICU mortality rate was 31.6%. Lower PEEP strategy treatment in L-type COVID-19 ARDS resulted in a PaO₂/FiO₂ ratio persistent daily improvement during the first 72 h of IMV. A lower PEEP strategy could be beneficial in the first phase of ARDS in critically ill COVID-19 patients.

Keywords: Adult respiratory distress syndrome; COVID-19; Mechanical ventilation; PaO2/FiO2; Positive-end-expiratory respiration.

Fig. 1

CLM COVID-19 patients. Management of COVID-19 patients evaluated at our COVID-19 center during two pandemic waves (from March 2nd to April 10th, 2020, and from October 5th, 2020, to January 15th, 2021). ICU admission was performed according to standard selection criteria (SpO₂ < 85% and/or dyspnea and/or signs of mental confusion). Patients not on invasive MV were excluded from the analysis.

Fig. 2

P/F ratio variation at OTI. P/F ratio variation before/after OTI at ICU admission (−75, CI 99%, −98/−52, p < 0.001)

Fig. 3

P/F ratio variation during MV. P/F ratio variation at ICU admission compared to the first, second, and third day of MV. All daily median PF values resulted significantly different compared to admission and compared to the day after, even with the use of low PEEP setting on MV. All differences resulted statistically significative (CI 99%, p < 0.001)