Patients with moderate to severe respiratory failure brought on by COVID-19 underwent capnodynamic monitoring of end-expiratory lung volume (EELVCO2<) and effective pulmonary blood flow (EPBF) while receiving a step increase in positive end-expiratory pressure (PEEP) of 50% above the baseline (PEEPlow to PEEPhigh). The key finding was a difference in arterial oxygen tension to inspired fraction of oxygen (P/F) ratio of more than 20 mm Hg between responders and non-responders. The secondary objectives were physiological dead space changes, correlations with independently measured recruited lung volume, and recruitment-to-inflation ratios with an instantaneous, one breath decrease in PEEP. Researchers gave group mean differences by mixed component ANOVA, correlations using Pearson’s correlation coefficient, and 95% CI for these correlations. About 15 of the 27 patients assessed responded when PEEPlow(11±2.7 cm H2O) was increased to PEEPhigh (18±3.0 cm H2O), raising the P/F ratio by 55 [24-86] mm Hg in comparison to 12 non-responders (P<0.01). Responders’ EELVCO2decreased by 461 [82-839] ml at PEEPlow(P=0.02), while there was no statistically significant difference between the groups at PEEPhigh. Respondents’ EELVCO2 and EPBF increased at PEEPhigh(r=0.56 [0.18-0.83], P=0.03). Comparatively to responders, non-responders demonstrated a negative relationship between increased lung capacity and decreased pulmonary perfusion (r=-0.65 [-0.12 to −0.89], P=0.02). Reduced dead space was observed in the respondents (-0.06 [-0.02 to -0.09]%, P<0.01). The recruitment-to-inflation ratio (r=0.87 [0.74-0.94], P<0.01) and recruited lung volume (r=0.85 [0.69-0.93], P<0.01) were linked with the decrease in EELVCO2. In mechanically ventilated patients with moderate to severe COVID-19 respiratory failure, improved oxygenation in response to greater PEEP was associated with higher end-expiratory lung capacity and pulmonary perfusion. Positive associations between the change in end-expiratory lung volume and the recruitment-to-inflation ratio and lung volume recruited were observed. This work demonstrates that capnodynamic monitoring can be utilised at the bedside to track physiological responses to PEEP. Positive associations between the change in end-expiratory lung volume and the recruitment-to-inflation ratio and lung volume recruited were observed. This work demonstrates the efficacy of capnodynamic monitoring to assess physiological reactions to PEEP at the bedside in order to provide an individualised PEEP setting.
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