Ventilatory Frequency Influences Accuracy of End-Tidal CO2 Measurements Analysis of Seven Capnometers

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Abstract
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 Data-scope 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 over-reported and three underreported PETCO2. At frequencies above 31 cycles/min, six capnometers underreported and one over-reported PETCO2. Errors may be clinically significant if they influence ventilator settings for patients.

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