Ventilatory Ratio Higher in Patients With COVID-19 vs Other Respiratory Failures

Among tracheotomized patients undergoing prolonged weaning, those with COVID-19 had significant differences in ventilation efficiency and respiratory mechanics, with higher ventilatory ratio (VRs) and mechanical power (MP), investigators reported in Therapeutic Advances in Respiratory Disease.

The retrospective, observational, cohort study aimed to determine the VR and MP distributions and trajectories in prolonged mechanically ventilated patients after COVID-19 pneumonia vs those with respiratory failures of other etiologies.

The COVID-19 group were consecutive patients with tracheostomies referred from intensive care units (ICUs) in Germany to a specialized weaning unit from March 2020 to June 2021. The control group, treated between October 2018 and June 2021, included tracheotomized patients with respiratory failure of other etiologies than COVID-19 who were ventilated and required prolonged weaning.

Both group’s VR and MP distributions were calculated at different time points, and a factorial repeated-measures analysis of variance (ANOVA) was conducted to detect within-subject time effects and between-group differences in the trajectories of ventilatory variables.

The analysis included 249 patients — 53 patients (median age, 65 years; 77.4% male) on prolonged mechanical ventilation after acute respiratory distress syndrome associated with laboratory-confirmed COVID-19 pneumonia, and 196 patients (median age, 69 years; 64.8% male) in the control group.

The patients with COVID-19 had higher respiratory rates, tidal volumes, and mechanical ventilation partial pressure of carbon dioxide in arterial blood (PaCO₂)  — all of which were associated with significantly increased minute ventilation and VRs throughout — median VR, 1.54 (interquartile range [IQR], 1.28-1.89) vs 1.27 (IQR, 1.08-1.50) at weaning onset, P <.01; and median VR, 1.38 (IQR, 1.19-1.73) vs 1.24 (IQR, 1.04-1.49) at weaning completion, P <.01.

Patients in the COVID-19 group also had consistently higher dynamic lung-thorax compliance (median LTC_dyn, 37 [IQR, 33-45] vs 35 [IQR, 28-43] mL/cmH₂O at weaning onset, P =.046; median LTC_dyn, 40 [IQR, 35-48] vs 37 [IQR, 30-44] mL/cmH₂O at weaning completion, P <.01) and MP (median MP, 26.0 [IQR, 22.1-31.1] vs 21.3 [IQR, 18.5-25.3] Joule/minute at weaning onset, P <.01; median MP, 24.2 [IQR, 20.8-28.6] vs 20.1 [IQR, 17.1-24.4] Joule/minute at weaning completion, P <.01).

Patients in the COVID-19 group had significantly lower weaning failure rates (9% vs 30%, P <.01), compared with the control group. In logistic regression analysis, VR and MP were independently associated with weaning failure in univariable analysis, but not in multivariable analysis.

The researchers noted that external validity is undetermined because the study is based on a monocentric approach. Also, the COVID-19 group had a low sample size, and information was lacking about intubation practices of most referring ICUs. In addition, diaphragm activation for ventilator triggering may have affected tidal volumes and, consequently, calculation of dynamic lung-thorax compliance and MP.

“COVID-19 patients demonstrated marked differences in ventilation efficiency and respiratory mechanics among prolonged mechanically ventilated individuals with tracheostomies, resulting in higher VRs and MP throughout weaning,” concluded the investigators. “The differences in MP were linked with higher lung-thorax compliance in COVID-19 patients, which may account for the lower weaning failure rate observed.”