Technical validation of the EMMA capnometer under hyperbaric conditions

Introduction: End-tidal carbon dioxide (ETCO2) monitoring is essential for monitoring intubated critical care patients, yet its use in hyperbaric environments can be problematic. We postulated that the EMMA mainstream capnometer may function accurately under hyperbaric conditions. Methods: Stage 1. The EMMA mainstream capnometer was tested at 101 kPa against a reference side-stream capnometer, Philips IntelliVue M3015B microstream, using 10 customised reference gases of various carbon dioxide (CO2) concentrations (2.47%−8.09%, or 18.5−60.7 mmHg at 101 kPa) in either air or oxygen. Stage 2. The functionality and accuracy of the EMMA capnometer was tested under hyperbaric conditions, 121–281 kPa, using the same test gases. Results: At 101 kPa, the EMMA capnometer measured CO2 at levels lower than expected (mean of differences = -2.5 mmHg (95% CI -2.1 to -2.9, P < 0.001)). The Philips capnometer measured CO2 more closely to expected CO2 (mean of differences = -1.1 mmHg (95% CI -0.69 to -1.4, P < 0.001). Both devices demonstrated a significant linear relationship with expected CO2. The EMMA capnometer functioned up to the maximum test pressure (281 kPa). The device over-read CO2 measurements at pressures > 141 kPa. Although variance increased at pressures in the therapeutic range for hyperbaric treatments, a significant linear relationship between expected and EMMA measured CO2 was demonstrated. The EMMA capnometer tolerated pressures to 281 kPa, but its display was limited to CO2 < 99 mmHg. Conclusions: This study validated EMMA capnometer function to 281 kPa in the hyperbaric environment. The device overread CO2 measurements at pressures >141 kPa, however there was a linear relationship between expected and measured CO2. The EMMA capnometer may be clinically useful for monitoring expired CO2 in patients undergoing hyperbaric oxygen treatment.