Transcutaneous PCO2 monitors are more accurate than end-tidal PCO2 monitors

Purpose. The accuracy of monitors for measuring transcutaneous P-CO2 (TcPCO2), end-tidal P-CO2 (EtPCO2), and nasal EtPCO2 was evaluated. Methods. The measuring devices included a TcPCO2 monitor (TCM3; Radiometer Trading), an EtPCO2 monitor (Ultima; Datex-Ohmeda), and a nasal EtPCO2 monitor (TG-920P; Nihon Kohden). The sensor electrode of the TCM3 TcPCO2 monitor was applied to the skin of the subject's upper arm. A sampling tube attached to the proximal end of the tracheal tube was connected to the Ultima EtPCO2 monitor. The miniature sensor of the TG-920P nasal EtPCO2 monitor was attached to the nostril. The values obtained were compared with direct measurements of arterial P-CO2(Pa-CO2) obtained by means of an ABL700 blood gas analyzer (Radiometer Trading) in surgically treated patients. The means +/- 2 SD of the differences between variables were calculated. Results. The TcPCO2 monitor (0.19 +/- 4.8 mmHg, mean +/- 2-SD) was more accurate than the EtPCO2 monitor (-4.4 +/- 6.5 mmHg, mean +/- 2-SD) in patients receiving artificial ventilation via an endotracheal tube and the TcPCO2 monitor was also more accurate than the nasal EtPCO2 monitor (-6.3 +/- 9.8 mmHg, bias +/- 2-SD) in patients breathing spontaneously. Conclusion. We found that the TcPCO2 monitor was more accurate than the EtPCO2 or nasal EtPCO2 monitor in surgically treated patients.