Fig. 2. Two-point sensor calibration line derivations for low (38.5-ppm) and high (385-ppm) carbon monoxide concentrations with nitrous oxide present. All volatile anesthetics (halothane, enflurane, isoflurane, desflurane, and sevoflurane) with nitrous oxide concentrations (45–64%) demonstrate negative deflection of the calibration points from room air control results. The average negative instrument bias approximated 13% for a nitrous oxide concentration of 60%.