Needle Direction Affects the Sensory Level of Spinal Anesthesia

Abstract

The effect of the direction of the spinal needle on the sensory level of anesthesia was investigated. Three ml plain bupi-vacaine 0.5%, previously equilibrated to 37°C, were injected intrathecally in two groups of twenty patients, who were kept sitting for three minutes after injection. In patients in group 1 a paramedian approach was used with an angle between the spinal needle and the patient's back of 50° or less. In patients in group 2 a median or paramedian approach was used, the resultant angle between the spinal needle and the patient's back being between 70° and 100°. The differences between segmental levels of sensory loss between groups 1 and 2 (T 3.4 and T 5.1, respectively) and of temperature loss (T 2.6 and T 4.2, respectively) 30 minutes after injection of bupivacaine were statistically significant. It is concluded that a steep paramedian approach of the subarachnoid space with an angle of less than 50° results in a cephalad spread averaging about 1.6 segments greater than when the needle is in the perpendicular position.