Partial pressure of end-tidal CO2 sampled via an intranasal catheter as a substitute for partial pressure of arterial CO2 in dogs

Objective: To demonstrate correlation and clinical usefulness of the partial pressure of end-tidal CO2 (ETCO2) measurement by nasal catheter placement in sedated dogs with and without concurrent nasal oxygen administration as a substitute for partial pressure of arterial CO2 (PaCO2). Design: Prospective, cross-over trial. Setting: University of Saskatchewan veterinary research laboratory. Animals: Six cross-breed dogs with a mean (+/- SD) weight of 29.1 +/- 4.03 kg. Interventions: All dogs were sedated with 5 mu g/kg medetomidine intravenously (IV) and an arterial catheter was placed in a dorsal pedal artery for removal of blood for gas analysis. A nasal catheter was placed in the ventral meatus and connected to a capnometer for ETCO2 measurements in all dogs. Dogs receiving supplemental nasal oxygen had a second nasal catheter placed in the contralateral naris. Measurements and main results: In the group without nasal oxygen supplementation, the ETCO2 measurement underestimated (negative bias) the PaCO2 by -2.20 mmHg with limits of agreement (95% confidence interval) of -5.79, 1.39 mmHg. In the group receiving oxygen supplementation, ETCO2 measurement underestimated (negative bias) the PaCO2 by -2.46 mmHg with limits of agreement (95% confidence interval) of -8.42, 3.50 mmHg. Conclusions: The results of this study demonstrate that ETCO2 monitoring via a nasal catheter provides a clinically acceptable substitute to arterial blood gas analysis as a means of monitoring ventilation in healthy, sedated dogs. The limits of agreement were within acceptable limits with and without concurrent insufflation of oxygen.