Subarachnoid bupivacaine blockade decreases midazolam and thiopental hypnotic requirements.
OBJECTIVE
To test the hypothesis that subarachnoid bupivacaine blockade decreases hypnotic requirements for thiopental sodium and midazolam.


METHODS
Randomized, double-blind, placebo-controlled study.


METHODS
Teaching hospital.


METHODS
53 nonpremedicated ASA physical status I and II adult male patients scheduled for elective lower abdominal, pelvic, or lower limb surgery.


METHODS
Intravenous injections of midazolam or thiopental were administered with or without subarachnoid bupivacaine blockade (12.5 mg) at the L3-L4 level. Thiopental or midazolam hypnotic requirements were determined using loss of ability to open eyes in response to verbal command as an endpoint. The thiopental requirements were determined by titration; the midazolam requirements were determined from dose-response curves obtained with bolus injections of predetermined doses of the drug.


RESULTS
Subarachnoid bupivacaine blockade decreased the hypnotic dose of thiopental from 3.40 +/- 0.68 mg/kg (mean +/- SD) with a dose range of 2.3 to 4.5 mg/kg (intramuscular saline) to 2.17 +/- 0.48 mg/kg with a dose range of 1.3 to 2.8 mg/kg (p < 0.005 for the difference). The ED50 value of midazolam decreased with the bupivacaine blockade, from 0.23 mg/kg (95% confidence limits: 0.08 to 0.38 mg/kg) to 0.06 mg/kg (0.01 to 0.14 mg/kg), with p < 0.0001 for the difference.


CONCLUSIONS
Subarachoid bupivacaine blockade decreases hypnotic requirements for both thiopental and midazolam. The results suggest that the reduction in hypnotic requirements is due to the decrease in afferent input induced by spinal anesthesia.
Tverskoy
M
M
Department of Anesthesiology, Rebecca Sieff Hospital, Safed, Israel.
Shagal
M
M
Finger
J
J
Kissin
I
I
D000328:Adult; D000344:Afferent Pathways / Q000187:drug effects; D000368:Aged; D000771:Anesthesia, Intravenous; D000775:Anesthesia, Spinal; D002045:Bupivacaine / Q000008:administration & dosage*; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D017558:Elective Surgical Procedures; D006801:Humans; D006993:Hypnotics and Sedatives / Q000008:administration & dosage*; D008297:Male; D008874:Midazolam / Q000008:administration & dosage*; D008875:Middle Aged; D009407:Nerve Block; D010919:Placebos; D013346:Subarachnoid Space; D013874:Thiopental / Q000008:administration & dosage*
D006993:Hypnotics and Sedatives; D010919:Placebos; D013874:Thiopental; D008874:Midazolam; D002045:Bupivacaine