Continuous monitoring of intrinsic PEEP based on expired CO kinetics: an experimental validation study.

Background: Quantification of intrinsic PEEP (PEEPi) has important implications for patients subjected to invasive mechanical ventilation. A new non-invasive breath-by-breath method (etCOD) for determination of PEEPi is evaluated.

Methods: In 12 mechanically ventilated pigs, dynamic hyperinflation was induced by interposing a resistance in the endotracheal tube. Airway pressure, flow, and exhaled CO were measured at the airway opening. Combining different I:E ratios, respiratory rates, and tidal volumes, 52 different levels of PEEPi (range 1.8-11.7 cmHO; mean 8.45 ± 0.32 cmHO) were studied. The etCOD is based on the detection of the end-tidal dilution of the capnogram. This is measured at the airway opening by means of a CO sensor in which a 2-mm leak is added to the sensing chamber. This allows to detect a capnogram dilution with fresh air when the pressure coming from the ventilator exceeds the PEEPi. This method was compared with the occlusion method.

Results: The etCOD method detected PEEPi step changes of 0.2 cmHO. Reference and etCOD PEEPi presented a good correlation (R 0.80, P < 0.0001) and good agreement, bias - 0.26, and limits of agreement ± 1.96 SD (2.23, - 2.74) (P < 0.0001).

Conclusions: The etCOD method is a promising accurate simple way of continuously measure and monitor PEEPi. Its clinical validity needs, however, to be confirmed in clinical studies and in conditions with heterogeneous lung diseases.