Anticholinergic Premedication for Sedation With Dexmedetomidine During Spinal Anesthesia

Before entering the operation room, patients are randomized in one group (A or C). For sedative premedication, all patients will be injected intramuscularly with midazolam 1mg. After entering the operation room, all patients will be monitored blood pressure, ECG and oxygen saturation. Before induction of spinal anesthesia, all patients will be loaded with plasma solution 5mL/kg. After induction of spinal anesthesia, block level will be checked. After fixation of block level, the loading dose(0.6ug/kg) of dexmedetomidine which is diluted with normal saline as 4ug/mL would be started for 10 minutes. However, just before starting dexmedetomidine,atropine .01~0.03mg/kg up to 0.5mg would be injected in group A. Otherwise normal saline 0.5mL would be injected in group C. The syringed would be blinding not to be noticed. After loading of dexmedetomidine, the diluted solution would be injected with 0.25ug/kg/hr until the end of the surgery. Every patients undergoing sedation would be applied the oxygen by nasal prong.

The heart rate decreasing 30% from initial heart rate or under 40/min would be regarded as bradycardia needing treatment, and atropine 0.5mg will be injected intravenously. Systolic blood pressure decreasing 30% from basal blood pressure or under 90 mm Hg would be regarded as hypotension needing treatment, and ephedrine 5mg will be injected intravenously. The number of medication treated would be noted.