Does monitoring end-tidal isoflurane concentration improve titration during general anesthesia?

Study Objective: To assess the value of end-tidal anesthetic gas monitoring with respect to intraoperative hemodynamic stability and recovery times. Design: Randomized blinded study. Setting: Operating rooms at a university teaching hospital. Patients: 120 ASA I and II patients receiving general anesthesia maintained with isoflurane and nitrous oxide (N₂O). Interventions: Following a standardized induction technique, patients were assigned to either an end-tidal isoflurane monitored (n = 60) or unmonitored (n = 60) group. During each operation, the anesthesiologist attempted to maintain an adequate "depth of anesthesia" by varying the administered concentration of isoflurane with or without information from an end-tidal isoflurane monitor. Intraoperative hemodynamic stability was assessed by determining the variation from a preincisional "baseline" mean arterial pressure (MAP) value established during a 10 minute interval immediately prior to the surgical incision. Recovery times were recorded from discontinuation of isoflurane and N₂O until awakening, orientation, and postanesthesia care unit discharge. Measurements and Main Results: Intraoperative hemodynamic stability was assessed in each patient and reported as the average error from the baseline MAP, absolute average error from the baseline MAP, coefficients of variation of heart rate (HR), systolic and diastolic MAP, and end-tidal isoflurane concentrations. Both study groups had similar intraoperative MAP and HR values, average error and coefficients of variation for the hemodynamic variables, as well as similar numbers of episodes of hypertension, hypotension, tachycardia, and bradycardia. Finally, the two groups were comparable with respect to early recovery times and postoperative side effects. Conclusions: This study suggests that end-tidal isoflurane monitoring does not improve the titration of isoflurane during general anesthesia.