Influence of Whitacre spinal needle orifice direction on the level of sensory blockade.

The purposes of the present study were to determine if the direction of the needle orifice during injection of anesthetic into the subarachnoid space, using a 25-gauge Whitacre spinal needle (Becton Dickinson, Franklin Lakes, NJ) to deliver 15 mg of 0.75% hyperbaric bupivacaine, affected the level of sensory blockade achieved, and if there was a difference in time from injection to surgical anesthesia based on needle orifice direction. A convenience sample was selected from patients presenting for elective surgical procedures. All patients received a standard anesthetic solution using a standard technique and duration of injection. Mean maximum height of sensory blockade was compared between treatment groups using a Student t test. Progression of the sensory blockade was compared at each data collection point using a chi-square test. There was no statistically significant difference in the mean maximum height of block between the treatment groups. The mean maximum height of block for the cephalad group was T4 with an SD of 2.5 dermatomes, and T5 with an SD of 4.57 dermatomes for the caudad group. An incidental finding was that all failed blocks were from the caudad group. There was no statistically significant difference in time from injection to surgical anesthesia between the treatment groups. Although the data support no statistically significant difference between the treatment groups for either research question, the cephalad group provides for a more precise height of block.