Using exhalation dynamics to evaluate PEEP levels in COVID-19 related ARDS

Background: We hypothesized that measured expiratory time constant (TauE) could be a bedside parameter for evaluation of PEEP settings in mechanically ventilated COVID-19 patients during pressure-controlled ventilation (PCV) mode. TauE is an easily measured parameter to assess lung physiology, even in non-homogeneous lungs including COVID-19 ARDS. Methods A prospective study was conducted including consecutively admitted adults (n = 16) with COVID-19 related ARDS requiring mechanical ventilation. Ventilator settings for all patients included: PCV, RR 18/min, constant inspiratory pressure 14 cmH 2 O, I:E ratio 1:1.5 and FiO 2 1.0. Escalating levels of PEEP (0 to 18 cmH 2 O) were applied and measured TauE and expiratory tidal volume (Vte) recorded. Next, a new parameter, TauE Index (TEI) was calculated (TEI = TauE * Vte) at each PEEP level in prone (n = 29) or supine (n = 24) positions. TEI maps were created to graphically show changes in individual physiology with PEEP. The PEEP setting with the highest TEI corresponded to the highest product of TauE and Vte and was considered the most suitable PEEP. Most suitable PEEP range was calculated as ± 10% from highest TEI. Results Two groups of patterns were observed in the TEI maps, recruitable (R) (75%) and non-recruitable (NR) (25%). In R group, the most suitable PEEP and PEEP range was 9±3 cmH 2 O and 6-12 cmH 2 O for prone position and 11±3 cmH 2 O and 7-13 cmH 2 O for supine position. In NR group, the most suitable PEEP and PEEP range was 7±3 cmH 2 O and 0-8 cmH 2 O for prone position and 4±2 cmH 2 O and 0-7 cmH 2 O for supine position, respectively. The R group showed significantly higher suitable PEEP (p<0.01) and PEEP ranges (p<0.01) than NR group. 45% of measurements resulted in most suitable PEEP being significantly different between the positions (p < 0.01). Conclusions Based on TEI mapping, responses to PEEP were easily measured. There was wide variation in patient responses to PEEP that indicate the need for personalized evaluation.