Validity of transcutaneous capnometry in prolonged use in a patient population with acute respiratory failure

BACKGROUND: Transcutaneous capnometry is a widespread method for monitoring carbon dioxide in respiratory care. Studies on its use in emergency medicine, the sensors long-term stability its practicability in this setting are lacking. This study aimed to clarify whether transcutaneous capnometry is a valid and feasible method for monitoring critically ill patients. METHODS: 100 patients with acute respiratory failure were monitored simultaneously with arterial blood gas analysis (paCO2) and transcutaneous capnometry (tcpCO2), using Radiometer TCM5, at baseline (T1) and after a maximum of 12 h (T2) an analyzed regarding clinically acceptable concordance and interruptions. RESULTS: Ninety-three patients (176 paired samples of paCO2 and tcpCO2) were included in the analysis. We found a good correlation between pCO2 and tcpCO2 (r = 0.9706) at T1, which weakened at T2 (r = 0.7760). However, the difference in the concordance of the measured values at T1 and T2 was not significantly different (p = 0.0545). Significantly frequent deviations between T1 and T2 occurred in patients with circulatory impairment (p = 0.0039). 22.9% of all values were outside the clinically acceptable range, but with paCO2 underestimated by tcpCO2 in only 5 cases (2.8%). In all clinically relevant deviations, we found an underlying technical error which would have been found by a trained examiner. CONCLUSIONS: trends. However, its successful application requires thorough knowledge of the analysis technique and potential sources of error. The validity of the method is limited in patients with significant circulatory dysregulation. Additionally, long-term use in clinical practice is often restricted by suboptimal patient conditions.