Monitoring anesthetic vapor concentrations using a piezoelectric detector: evaluation of the Engstrom EMMA.

The Engstrom anesthetic gas analyzer (EMMA) was evaluated to determine the reproducibility, response time, gas interference, water vapor dependence, and sensitivity. The analyzer also was evaluated clinically in 20 children undergoing orthopedic surgery. Difference between the analyzer output and anesthetic gas standard (reproducibility) ranged from 0.013 +/- 0.008 vol % to 0.018 +/- 0.018 vol %. Response times decreased from 710 ms at 5 l X min-1 to 149 ms at 30 l X min-1. Nitrous oxide caused an offset of +0.11 +/- 0.007 vol %. Water vapor caused positive offsets of 0.25 +/- 0.044 vol %, 0.51 +/- 0.027 vol %, and 0.80 +/- 0.037 vol % at 25 degrees C, 30 degrees C, and 34 degrees C, respectively. The analyzer reproducibly measured dry gas concentrations, but compensation had to be made for water vapor when measuring wet gases. The analyzer's usefulness for end-tidal monitoring was questioned because of its slow response time and its sensitivity to water vapor.