Etomidate versus Thiopental for Induction of Anesthesia

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Abstract
Hemodynamic changes and side effects of anesthesia induction with etomidate or thiopental were evaluated in 83 ASA [American Society of Anesthesiologists] class I or II patients. Patients were randomly assigned to 1 of 12 groups according to pretreatment drug (fentanyl, 100 .mu.g or normal saline i.v.), induction agent (etomidate, 0.4 mg/kg or thiopental, 4 mg/kg), and maintenance anesthetic technique (isoflurane-oxygen, isoflurane-nitrous oxide-oxygen or fentanyl-nitrous oxide-oxygen). The aim of this experiment, of factorial design, was to evaluate the combined effects of 2 or more experimental variables used simultaneously and to observe interaction effects. There were significant increases in heart rate in all groups, especially after tracheal intubation. These increases were attenuated but not eliminated by fentanyl pretreatment. Systolic arterial blood pressure increased significantly after intubation and was unaffected either by fentanyl pretreatment or by the induction agent. Patients in whom anesthesia was induced with etomidate had a greater incidence of pain on injection and myoclonus and a lesser incidence of apnea than patients in whom anesthesia was induced with thiopental. Fentanyl pretreatment significantly decreased the incidence of pain on injection and myoclonus, but it increased the incidence of apnea when anesthesia was induced with etomidate. The incidence of postoperative nausea and vomiting was similar after thiopental and etomidate and was unaffected by fentanyl pretreatment. Patients in whom anesthesia was maintained with isoflurane (with and without nitrous oxide) had a significantly lower incidence of nausea and vomiting than did patients given fentanyl-N2O-O2 for maintenance of anesthesia. There evidently is no significant difference between etomidate and thiopental as anesthetic induction agents in healthy patients. Pretreatment with a small dose of fentanyl attenuates the increases in heart rate associated with induction of anesthesia and tracheal intubation with either etomidate or thiopental and reduces but does not eliminate side effects associated with etomidate induction.