DOES MONITORING END-TIDAL ISOFLURANE CONCENTRATION IMPROVE TITRATION DURING GENERAL-ANESTHESIA

Study Objective: To assess the value of end-tidal anesthetic gas monit oring with respect to intraoperative hemodynamic stability and recover y times. Design: Randomized blinded study. Setting: Operating rooms at a university teaching hospital. Patients: 120 ASA I and II patients r eceiving general anesthesia maintained with isoflurane and nitrous oxi de (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 anest hesiologist attempted to maintain art adequate ''depth of anesthesia'' by varying the administered concentration of isoflurane with or witho ut information from an end-tidal isoflurane monitor. Intraoperative he modynamic stability was assessed by determining the variation from a p reincisional ''baseline'' mean arterial pressure (MAP) value establish ed during a 10 minute interval immediately prior to the surgical incis ion. Recovery times were recorded from discontinuation of isoflurane a nd N2O until awakening, orientation, and postanesthesia care unit disc harge. Measurements and Main Results: Intraoperative hemodynamic stabi lity was assessed in each patient and reported as the average error fr om the baseline MAP, absolute average error from the baseline MAP, coe fficients of variation of heart rate (HR), systolic and diastolic MAP, and end-tidal isoflurane concentrations. Both study groups had simila r 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 suggest s that end-tidal isoflurane monitoring does not improve the titration of isoflurane during general anesthesia.