ABSTRACT
Factors which may influence the extent of spinal anesthesia include gravity, baricity, volume, doee and concentration of the injected local anesthetic solution, and patient position. We have often experienced unexpected high level of spinal anesthesia and incomplete muscle relaxation when 0.1% tetracaine mixed in distilled water was injected intradurally for the perianal operation in jack-knife position as hypobaric technique. We have done this study to see whether injected volume or patient position influence the level for the perianal surgery. Fourty-eight patients were divided into two groups, group I, 0.1% tetracaine 5 ml, n=24, and group 11, 0.4% tetracaine 1.25 ml, n=24 in the jack-knife position of which cephalad downward angle was 15 degree, 18degree and 23degree. Sensory dermatomal levels of anesthesia were assesed using loss of pinprick aensation at 5 min and 30 min following completion of injection. Results are as follows: 1) Tetracaine mixtures of both groups were consistently hypobaric compared to patient CSF. 2) In both groups, there were significant differences in the sensory block level between 15degree and 18degree and 15degree and 23degree position but no difference between 18degree and 23degree position after 30 min. 3) Level of anesthesia were higher after 30 min than 5 min in the both groups. 4) The effect of volume of injected anesthetic solution could not be seen in the bath groups.