Dose-finding study of intravenous midazolam for sedation and amnesia during spinal anesthesia in patients premedicated with intramuscular midazolam.

PURPOSE

We investigated the effective and safe dose of intravenous midazolam for sedation and amnesia during spinal anesthesia in patients premedicated with intramuscular midazolam.

METHODS

One hundred and eighty patients aged 20-50 years scheduled for spinal anesthesia received midazolam 0.06 mg.kg(-1) and atropine 0.01 mg.kg(-1) intramuscularly 15 min before entering the operating room. Spinal anesthesia was performed with 0.5% hyperbaric tetracaine. Five minutes after starting surgery, midazolam 0 (control group), 0.01, 0.02, 0.03, 0.04, or 0.05 mg.kg(-1) was intravenously administered (30 patients each). Blood pressure, heart rate, respiratory rate, percutaneous oxygen saturation (S(p)(O)(2)), verbal response, eyelash reflex, and involuntary body movement were measured every 5 min for 30 min. Memory during surgery was also investigated.

RESULTS

The number of the patients with loss of verbal response, with loss of eyelash reflex, and with no memory during surgery were significantly larger in the groups receiving midazolam >or=0.03 mg.kg(-1), >or=0.04 mg.kg(-1), and >or=0.02 mg.kg(-1), respectively. The decrease in blood pressure or increase in respiratory rate with decrease in S(p)(O)(2) was significantly larger in the groups receiving midazolam >or=0.03 mg.kg(-1) or 0.05 mg.kg(-1), respectively.

CONCLUSION

For sedation and amnesia of the patients aged 20-50 years in spinal anesthesia with about 1 h duration receiving intramuscular midazolam 0.06 mg.kg(-1) as a premedication, intravenous midazolam 0.02 mg.kg(-1) might be effective and safe.