Continuous monitoring of intrinsic PEEP based on expired CO2 kinetics: an experimental validation study

Quantification of intrinsic PEEP (PEEPi) has important implications for patients subjected to invasive mechanical ventilation. A new non-invasive breath-by-breath method (etCO 2 D) for determination of PEEPi is evaluated. In 12 mechanically ventilated pigs, dynamic hyperinflation was induced by interposing a resistance in the endotracheal tube. Airway pressure, flow, and exhaled CO 2 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 cmH 2 O; mean 8.45 ± 0.32 cmH 2 O) were studied. The etCO 2 D 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 2 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. The etCO 2 D method detected PEEPi step changes of 0.2 cmH 2 O. Reference and etCO 2 D PEEPi presented a good correlation ( R 2 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). The etCO 2 D 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.