Evaluation of two commercially available carbon dioxide sampling nasal cannulae

Our study compared two commercially available carbon dioxide sampling nasal cannulae for efficacy of oxygenation and relationship of end-tidal carbon dioxide (PETCO2) to arterial carbon dioxide (PaCO2). The two-prong nasal cannula (2PNC) has one prong dedicated to delivering O2 via one naris and the second prong dedicated to sampling exhaled gases via the other naris. The four-prong nasal cannula (4PNC) delivers O2 via a prong in each naris, and samples exhaled gases via another set of prongs in each naris. Forty six patients were divided into three groups, which received either 2 (n = 15), 3 (n = 16), or 4 (n = 15) L/min O2, respectively, and were studied sequentially with standard nasal cannula (SNC), the 2PNC, and then the 4PNC. At each O2 flow rate, PaO2 was equivalent regardless of whether the SNC, 2PNC, or 4PNC was used. Seventy-four percent (34/46) of the 2PNC and 0% (0/46) of the 4PNC PETCO2 values were within +/- 4 torr of the PaCO2 value. The authors conclude that the 2PNC and 4PNC are equally effective compared with an SNC in oxygenating patients, but the PETCO2 measured by the 2PNC provides a superior quantitative estimate of the PaCO2 than that obtained by the 4PNC.