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.