Capnographic monitoring of extubated postoperative patients

Postoperative respiratory monitoring of surgical patients requires assessment of both oxygenation and ventilation. Arterial blood gas (ABG) measurements traditionally have been used to detect elevated arterial carbon dioxide (PaCO2) concentrations. The recent availability of a noninvasive technique for end-tidal CO2 measurements (EtCO2) may allow substitution of this real-time modality for the more cumbersome blood gas determinations. This study examines 41 extubated postoperative patients monitored with both modalities and evaluates whether capnography can replace routine blood gas determinations in selected patients. Paired ABG and EtCO2 measurements were obtained at 30 and 90 min after admission to the recovery room. A new nasopharyngeal catheter was employed to obtain exhaled gas samples for EtCO2 measurement. Overall, EtCO2 was lower than PaCO2 by 2.8 torr (p < .05), with a precision of +/- 2.6 torr. Correlation between EtCO2 and PaCO2 was excellent (r = 0.87, p < .01). We conclude that on-line EtCO2 measurements provide a useful substitute for routine ABG determinations of PaCO2 in selected patients. The nasopharyngeal catheter provides both a patent airway and undiluted gas for evaluation. This methodology can improve patient comfort and safety considerably while decreasing cost and discomfort.