Ventilatory frequency influences accuracy of end-tidal CO2 measurements. Analysis of seven capnometers.

An accurate high-frequency response is mandatory when end-tidal CO2 (PETCO2) is monitored during pediatric general anesthesia. The purpose of this study was to assess the accuracy of six infrared-based capnometers and one multiplexed mass spectrometer available at our institution at increasing frequency. Capnometers studied were the Datascope Accucap, Hewlett-Packard 47210A capnometer, Narkomed 3 Capnomed, Novametrix Capnogard model 1250, Perkin-Elmer Advantage, Puritan-Bennett Datex CO2 monitor, and Traverse Medical Monitor model 2200 capnometer. Changes in CO2 concentration were generated by a solenoid valve switching between 100% O2 and 7% CO2 in O2. Frequencies, 8-101 cycles/min were chosen to stimulate a range that might be generated by children during general endotracheal anesthesia. At every rate the displayed PETCO2 was recorded. Differences in displayed PETCO2 from known CO2 ranged from -16.4 to +6.6. At or below frequencies of 31 cycles/min, four capnometers overreported and three underreported PETCO2. At frequencies above 31 cycles/min, six capnometers underreported and one overreported PETCO2. Errors may be clinically significant if they influence ventilator settings for patients.