Mechanical power ratio and respiratory treatment escalation in COVID-19 pneumonia: a secondary analysis of a prospectively enrolled cohort

Background: Under the hypothesis that mechanical power ratio could identify the spontaneously breathing patients with higher risk of respiratory failure, we assessed lung mechanics in non-intubated patients with COVID-19 pneumonia aimed at: 1) describe their characteristics; 2) compare lung mechanics between patients who received respiratory treatment escalation and those who did not; 3) identify variables associated with the need for respiratory treatment escalation. Methods: Secondary analysis of prospectively enrolled cohort involving 111 consecutive spontaneously breathing adults receiving continuous positive airway pressure, enrolled from September 2020 to December 2021. Lung mechanics, other previously reported predictive indices were calculated, as well as a novel variable: the mechanical power ratio (the ratio between the actual and the expected baseline mechanical power). Patients were grouped according to the outcome: 1) no-treatment escalation (patient supported in continuous positive airway pressure until improvement); 2) treatment escalation (escalation of the respiratory support to non-invasive or invasive mechanical ventilation); and the association between lung mechanics/predictive scores and outcome was assessed. Results: At day 1, patients undergoing treatment escalation had similar spontaneous tidal volume than patients who did not (7.1 ± 1.9 vs 7.1 ± 1.4 mL/KgIBW; p=0.990). In contrast, they showed higher respiratory rate (20 ± 5 vs 18 ± 5 bpm; p=0.028), minute ventilation (9.2 ± 3.0 vs 7.9 ± 2.4 L/min; p=0.011), tidal pleural pressure (8.1 ± 3.7 vs 6.0 ± 3.1 cmH2O; p=0.003), mechanical power ratio (2.4 ± 1.4 vs 1.7 ± 1.5; p=0.042) and lower PaO2/FiO2 (174 ± 64 vs 220 ± 95; p=0.007). Mechanical power (AUC 0.738 [95%CI 0.636-0.839] p<0.001), the mechanical power ratio (AUC 0.734 [95%CI 0.625-0.844] p <0.001) and the pressure-rate index (AUC 0.733 [95%CI 0.631-0.835] p <0.001) showed the highest AUC. Conclusions: In this COVID-19 cohort, tidal volume was similar in patients undergoing treatment escalation and in patients who did not; mechanical power, its ratio, and pressure-rate index were the variables presenting the highest association with the clinical outcome.