Intraoperative PEEP selection by pressure-based capnography: a proof of concept study

We aimed to test a new method to determine the positive-end expiratory pressure (PEEP) that maintains the lungs open after a recruitment maneuver (RM).

In eleven anesthetized patients, we compared the standard RM searching for the optimal PEEP based on the highest respiratory compliance (PEEP_Crs), with a new method. This method performs a RM during a slow pressure-volume curve and detects the optimal PEEP using the novel barometric capnography curve (BCap); i.e. the plot of expired carbon dioxide versus airway pressure. The lungs' closing pressure was detected when the slope of phase III of the BCap changed along this slow expiration (PEEP_BCap). The main objective was to compare PEEP_BCap with the reference PEEP_Crs. As a secondary objective, we explored the association between PEEP_BCap and the polarity change in end-expiratory transpulmonary pressure (PEEP_PL) during the deflation phase of a slow flow PV curve.

We found a PEEP_BCap of 8.5(3.3) cmH₂O that was no statistically different from the PEEP_Crs of 10.0(4.0) cmH₂O (p = 0.72). Both methods correlated well with a Rho of 0.84 (p < 0.001). The Bland-Altman plot showed a bias of 0.19 and LOA of 1.92 cmH₂O (95%CI -0.39 to 0.77 cmH₂O). During the PV slow deflation limb, PEEP_PL was 9.3(4.3), which was statistically similar to PEEP_BCap (p = 0.61). Both pressures were strongly correlated (Rho = 0.93, p < 0.001) with a bias of -0.3 cmH₂O and LOA of 1.52 (95%CI -0.76 to 0.16 cmH₂O).

We concluded that BCap is feasible to detect lungs collapse using a constant flow PV curve.