Effects of end-tidal gas monitoring and flow rates on hemodynamic stability and recovery profiles

This study was designed to evaluate the impact of routine end-tidal anesthetic gas monitoring on the intraoperative hemodynamic stability and early recovery profile in 253 consenting ASA physical status I-III patients undergoing elective otolaryngologic procedures with isoflurane or enflurane anesthesia. Patients were randomly assigned to one of six treatment groups: Group I, monitored high-flow isoflurane; Group II, unmonitored high-flow isoflurane; Group III, monitored low-flow isoflurane; Group IV, unmonitored low-flow isoflurane; Group V, monitored low-flow enflurane; or Group VI, unmonitored low-flow enflurane. After a standardized induction sequence, anesthesia was maintained by administering variable concentrations of isoflurane or enflurane in an air/oxygen mixture at two different total gas flow rates (0.7 L/min or 3.5 L/min, respectively). Mean arterial pressure (MAP), heart rate (HR), and end-tidal (ET) anesthetic concentrations were recorded by a computer throughout the operation. The resident anesthesiologist was instructed to maintain an adequate 'depth of anesthesia' by varying the administration of isoflurane (Groups I-IV) or enflurane (Groups V and VI) with or without end-tidal gas monitoring. Intraoperative hemodynamic stability was assessed in each patient and reported as the average error from the preincisional (baseline) MAP, average absolute error from the baseline MAP, coefficients of variation for HR, systolic, diastolic, and MAP values, and ET anesthetic concentrations. Recovery times from discontinuation of the volatile drug until awakening, following commands, and postanesthesia care unit (PACU) discharge were recorded. The six study groups had similar intraoperative MAP and HR values, coefficients of variation, and numbers of episodes of hypertension, hypotension, tachycardia, and bradycardia. The groups were also similar with respect to early recovery times and postoperative side effects. In conclusion, end-tidal anesthetic monitoring did not improve intraoperative hemodynamic stability or decrease emergence times from general anesthesia with isoflurane or enflurane, even when low gas flows (0.7 L/min) were used in this patient population.