Mechanical power normalized to aerated lung predicts noninvasive ventilation failure and death and contributes to the benefits of proning in COVID-19 hypoxemic respiratory failure

Abstract

Background: Concern exists that noninvasive ventilation (NIV) may promote ventilation-induced lung injury(VILI) and worsen outcome in acute hypoxemic respiratory failure (AHRF). Different individual ventilatory variables have been proposed to predict clinical outcomes, with inconsistent results. Mechanical power (MP), a measure of the energy transfer rate from the ventilator to the respiratory system during mechanical ventilation, might provide solutions for this issue in the framework of predictive, preventive and personalized medicine (PPPM). We explored (1) the impact of ventilator-delivered MP normalized to well-aerated lung (MPWAL) on physio-anatomical and clinical responses to NIV in COVID-19-related AHRF and (2) the effect of prone position(PP) on MPWAL. Methods: We analyzed 216 noninvasively ventilated COVID-19 patients (108 patients receiving PP + NIV and 108 propensity score-matched patients receiving supine NIV) with moderate-to-severe(paO2/FiO2 ratio < 200) AHRF enrolled in the PRO-NIV controlled non-randomized study (ISRCTN23016116). Quantification of differentially aerated lung volumes by lung ultrasonography (LUS) was validated against CT scans. Respiratory parameters were hourly recorded, ABG were performed 1 h after each postural change. Time-weighed average values of ventilatory variables, including MPWAL, and gas exchange parameters (paO2/FiO2 ratio, dead space indices) were calculated for each ventilatory session. LUS and circulating biomarkers were assessed daily. Results: Compared with supine position, PP was associated with a 34% MPWAL reduction, attributable largely to an absolute MP reduction and secondly to an enhanced lung reaeration. Patients receiving a high MPWAL during the 1st 24 h of NIV [MPWAL(day 1)] had higher 28-d NIV failure (HR = 4.33,95%CI:3.09 − 5.98) and death (HR = 5.17,95%CI: 3.01 − 7.35) risks than those receiving a low MPWAL(day 1). In Cox multivariate analyses, MPWAL(day 1) remained independently associated with 28-d NIV failure (HR = 1.68,95%CI:1.15–2.41) and death (HR = 1.69,95%CI:1.22–2.32). MPWAL(day 1) outperformed other power measures and ventilatory variables as predictor of 28-d NIV failure (AUROC = 0.89;95%CI:0.85–0.93) and death (AUROC = 0.89;95%CI:0.85–0.94). MPWAL(day 1) predicted also gas exchange, ultrasonographic and inflammatory biomarker responses, as markers of VILI, on linear multivariate analysis. Conclusions: In the framework of PPPM, early bedside MPWAL calculation may provide added value to predict response to NIV and guide subsequent therapeutic choices i.e. prone position adoption during NIV or upgrading to invasive ventilation, to reduce hazardous MPWAL delivery, prevent VILI progression and improve clinical outcomes in COVID-19-related AHRF.