Detection of hypoventilation during deep sedation in patients undergoing ambulatory gynaecological hysteroscopy: a comparison between transcutaneous and nasal end-tidal carbon dioxide measurements

Abstract

BackgroundTranscutaneous measurement of carbon dioxide (Tcco2) provides a non-invasive estimation of arterial carbon dioxide (Paco2). Nasal capnography (Pe′co2) is used to assess ventilation during monitored anaesthesia care (MAC) with sedation since it can readily detect apnoea. We compared the agreement between Tcco2 and Pe′co2 with Paco2 and the ability to detect hypercarbia in patients under deep sedation. MethodsForty healthy female subjects receiving deep sedation for hysteroscopy were studied. A Tcco2 (TOSCA 500, Radiometer, Inc., Westlake, OH, USA) electrode was applied to the earlobe and Pe′co2 capnography was monitored using nasal side-stream sampling. All subjects received oxygen (3 litre min−1). Subjects were evaluated at intervals using a modified Ramsay sedation score until they reached a score ≥5. Arterial blood gas values were compared with Tcco2 and Pe′co2 values. Bland–Altman, linear regression, and receiver operator characteristics analysis were performed. ResultsThe mean (sd) absolute difference between the Tcco2, Pe′co2, and the Paco2 were 0.43 (0.35) and 1.06 (0.8) kPa, respectively (P=0.002). Tcco2 demonstrated a mean bias (2 sd) of 0.23 (0.07–0.4) kPa with Paco2 compared with −0.93 (−1.24 to −0.63) kPa for Pe′co2. One minute before blood sampling, the sensitivity of the Tcco2 monitor for detecting Paco2 >6.65 kPa was greater than for Pe′co2 (66.7% vs 33.3%, P<0.01). ConclusionsTcco2 demonstrated better agreement with Paco2 than Pe′co2 for patients under MAC with deep sedation. Tcco2 monitoring was more sensitive for detection of Paco2 >6.65 kPa than Pe′co2.