A Comparison of Carbon Dioxide Monitoring and Oxygenation between Facemask and Divided Nasal Cannula

Abstract

The divided nasal cannula is a device recently released in Australia that couples oxygen delivery and end-tidal carbon dioxide (P_ET CO₂) monitoring. This study compares the accuracy of P_ET CO₂ measurements by the divided nasal cannula and those measured by a modified facemask (as currently used in this institution), with arterial partial pressure of carbon dioxide (P_aco₂). In this crossover study, 30 patients who had arterial lines as part of their routine monitoring were given oxygen via nasal cannula and facemask preoperatively. The P_ETCO₂ was measured with each device and a simultaneous P_aco₂ and P_ao₂ measured after equilibration. The results demonstrate a significant difference between the P_ET CO₂ as measured by each technique. The divided nasal cannula more accurately reflects P_aco₂ (mean arterial to end expired gradient of 5 mmHg) and provides a more representative trace when compared to a traditional facemask system. Both methods provided adequate oxygenation.