Determining respiratory rate using measured expiratory time constant: A prospective observational study.

PURPOSE: Potential negative implications associated with high respiratory rate (RR) are intrinsic positive end-expiratory pressure (PEEPi) generation, cardiovascular depression and possibly ventilator induced lung injury. Despite these negative consequences, optimal RR remains largely unknown. We hypothesized that without consideration of dynamics of lung emptying (i.e., the expiratory time constant [RCEXP]) clinician settings of RR may exceed the frequency needed for optimal lung emptying. MATERIALS AND METHODS: This prospective multicenter observational study measured RCEXP in 56 intensive care patients receiving pressure-controlled ventilation. We compared set RR to the one predicted with RCEXP (RRP). Also, the subgroup of patients with prolonged RCEXP was analyzed. RESULTS: Overall, the absolute mean difference between the set RR and RRP was 2.8 bpm (95% CI: 2.3-3.2). Twenty-nine (52%) patients had prolonged RCEXP (>0.8 s), mean difference between set RR and RRP of 3.1 bpm (95% CI: 2.3-3.8; p < 0.0001) and significantly higher PEEPi compared to those with RCEXP ≤ 0.8 s: 4.4 (95% CI: 3.6-5.2) versus 1.5 (95% CI: 0.9-2.0) cmH2O respectively, p < 0.0001. CONCLUSIONS: Use of RRP based on measured RCEXP revealed that the clinician-set RR exceeded that predicted by RCEXP in the majority of patients. Measuring RCEXP appears to be a useful variable for adjusting the RR during mandatory mechanical ventilation.

Programmed multi-level ventilation in COVID-19-related acute respiratory distress syndrome: a multi-center retrospective observational study.

OBJECTIVE: We evaluated pressure-controlled ventilation (PCV) with multiple programmed levels of positive end expiratory pressure (programmed multi-level ventilation; PMLV) in patients with coronavirus disease 2019 (COVID-19)-related acute respiratory distress syndrome (ARDS). METHODS: We conducted a multicenter, retrospective study from November 2020 to February 2021. PMLV was used with PCV in all patients with intensive care admission until improvement in oxygenation (fraction of inspired oxygen [FiO2] ≤0.50 and oxygen saturation [SpO2] >92%). The observed outcomes were improvement of hypoxemia, length of mechanical ventilation, partial pressure of carbon dioxide (PaCO2) stability, and adverse events. RESULTS: Of 188 mechanically ventilated patients with COVID-19-related ARDS, we analyzed 60 patients treated with PMLV. Hypoxemia improved in 55 (92%) patients, as measured by the change in partial pressure of oxygen/FiO2 and SpO2/FiO2 ratios on day 3 versus day 1, and in 32 (66%) ventilated patients on day 7 versus day 3. The median (interquartile range) length of mechanical ventilation for survivors and non-survivors was 8.4 (4.7-14.9) and 6.7 (3.6-10.3) days, respectively. CONCLUSIONS: PMLV appears to be a safe and effective ventilation strategy for improving hypoxemia in patients with COVID-19-related ARDS. Further studies are needed comparing the PMLV mode with the conventional ARDS ventilatory approach.