TITLE: COMAINTENANCE OF ANESTHESIA AND PLANNED AWAKENING: A NEW TECHNIQUE FOR AMBULATORY SURGERY

AUTHORS: Ronald Vinik, MD
AFFILIATION: University of Alabama at Birmingham, Birmingham, AL.

INTRODUCTION: Propofol and midazolam are synergistic for induction of anesthesia. The induction dose of propofol can be reduced by 45% by the addition of 1/10 of the ED50 of midazolam (0.02 mg/kg)¹. A similar reduction in the maintenance infusion of propofol from 100 mg/kg/minute to 50 mg/kg/minute can be achieved by a simultaneous infusion of midazolam in subhypnotic doses.
HYPOTHESIS: The concurrent use of two subhypnotic doses of propofol and midazolam will synergistically produce adequate anesthesia for strabismus surgery, which can be antagonized with flumazenil, and the patient will be sufficiently alert to perform rapid saccadic eye movement within 10 minutes of the end of surgery, which will enable the surgeon to make final adjustments of the eye muscle in the operating room, instead of next day.
METHODS: 50 IRB approved, ASA 1+2 consenting adult patients aged 18-65 undergoing strabismus surgery with adjustable suture were randomly induced with midazolam 2 mg, fentanyl 100 mg, and 1-1.5 mg/kg propofol. Anesthesia was maintained with a stepped-down infusion of propofol, (10 minute intervals) 167, 133 and 100 mg/kg/minute (control group P100). Test group: Infusion further reduced to 50 mg/kg/minute of propofol + 1 mg/kg/minute of midazolam (P50). All patients breathed 65% N₂O spontaneously with LMA. Five minutes after surgery the P50 group received 0.4 mg of flumazenil. Bispectral index (BIS) monitoring was used on all patients.
CONCLUSIONS: Comaintenance of anesthesia with mida- zolam and propofol reduces the conventional maintenance infusion dose of propofol by approximately 50% and is a practical, realistic technique for ambulatory surgery. Control of recovery is predictable and consistent in the antagonized group. Additionally, the patients have no recall for surgery or adjustment of suture 20 minutes after surgery. This is a cost effective technique for patient, surgeon and institution. BIS values correlated appropriately with hemodynamics, spontaneous respiratory rate and ETCO₂.
REFERENCE:

1.) Triple anesthetic combination: Propofol-midazolam- alfentanil. Anesth Analg 78:354-58, 1994.