Time constant to determine PEEP levels in mechanically ventilated COVID-19 ARDS: a feasibility study

BACKGROUND: We hypothesized that the measured expiratory time constant (TauE) could be a bedside parameter for the evaluation of positive end-expiratory pressure (PEEP) settings in mechanically ventilated COVID-19 patients during pressure-controlled ventilation (PCV). METHODS: A prospective study was conducted including consecutively admitted adults (n = 16) with COVID-19-related ARDS requiring mechanical ventilation. A PEEP titration using PCV with a fixed driving pressure of 14 cmH(2)O was performed and TauE recorded at each PEEP level (0 to 18 cmH(2)O) in prone (n = 29) or supine (n = 24) positions. The PEEP setting with the highest TauE (TauE(MAX)) was considered to represent the best tradeoff between recruitment and overdistention. RESULTS: Two groups of patterns were observed in the TauE plots: recruitable (R) (75%) and nonrecruitable (NR) (25%). In the R group, the optimal PEEP and PEEP ranges were 8 ± 3 cmH(2)O and 6–10 cmH(2)O for the prone position and 9 ± 3 cmH(2)O and 7–12 cmH(2)O for the supine position. In the NR group, the optimal PEEP and PEEP ranges were 4 ± 4 cmH(2)O and 1–8 cmH(2)O for the prone position and 5 ± 3 cmH(2)O and 1–7 cmH(2)O for the supine position, respectively. The R group showed significantly higher optimal PEEP (p < 0.004) and PEEP ranges (p < 0.001) than the NR group. Forty-five percent of measurements resulted in the most optimal PEEP being significantly different between the positions (p < 0.01). Moderate positive correlation has been found between TauE vs C(RS) at all PEEP levels (r(2) = 0.43, p < 0.001). CONCLUSIONS: TauE may be a novel method to assess PEEP levels. There was wide variation in patient responses to PEEP, which indicates the need for personalized evaluation.