Cross-sensitivity in water vapor in the Engstrom EMMA
Halothane, enflurane, and isoflurane vapor concentrations (0-3%) were simultaneously measured by a calibrated Engstrom EMMA and Beckman LB-2 gas analyzer, and were heated and/or humidified by an inline Bird humidifier. Data were treated by regression analysis for lines of best fit. Water vapor produced increasing cross-sensitivity as a function of temperature in all vapors measured by the Engstrom EMMA but not in the Beckman LB-2. At 38°C cross-sensitivity by water vapor was 0.97, 0.92, and 1.12 volumes percent reading for halothane, enflurame, and isoflurane, respectively. Water vapor cross-sensitivity with the EMMA in the isoflurane selector position was statistically higher (P < 0.05) than in the other two positions. We conclude that water vapor cross-sensitivity in the Engstrom EMMA is in excess of the manufacturer's specifications (0.3 volumes percent at 37°C) and different with respect to the anesthetic gas being measured.