Inspiratory effort estimated by airway occlusion pressure in the presence of intrinsic positive end-expiratory pressure

In patients with auto- or intrinsic positive end-expiratory pressure (PEEPi), a portion of the inspiratory effort is spent to overcome PEEPi before lung inflation begins. End-expiratory whole-breath airway occlusion pressure (ΔPocc) is a useful tool to estimate inspiratory muscle pressure (ΔPmus) but it may not capture this component. We retrospectively analyzed data from patients with various degrees of PEEPi enrolled in a study who underwent PEEP titration during pressure support ventilation (PSV) with esophageal pressure (Pes). Inspiratory effort was partitioned into the effort generated before inflation and the effort required for ventilator triggering and inflation. ΔPmus, Pes swing (ΔPes) and dynamic transpulmonary pressure (ΔPL,dyn) were both measured and predicted from ΔPocc using established conversion factors. Linear mixed-effects models were used to evaluate the effect of PEEPi on estimation accuracy. The results showed that 1) PEEPi values ranged from mean (±SD) of 4.7 (±5.0) to 1.2 (±0.7) cmH2O from PEEP 2 to 14; 2) ΔPocc does not represent the total inspiratory effort when PEEPi or relaxation of active expiration is present, and is limited to the triggering and inflation components; 3) when the airway pressure following ΔPocc exhibits a visible stable plateau, PEEPi may be estimated under selected waveform conditions on the ventilator screen; 4) Baydur’s maneuver for esophageal balloon calibration might be biased in case of PEEPi or active expiration; 5) the predicted estimate of ΔPL,dyn appears acceptable at group level but can lack precision. Conclusion: this proof-of-concept study shows that ΔPocc may underestimate inspiratory effort in case of PEEPi. When a plateau airway pressure can be observed in the end of ΔPocc, it seems possible to estimate PEEPi noninvasively.