Depth of spinal needle insertion and its associated factors among patients who underwent surgery under spinal anesthesia

Background: Lumbar puncture is a difficult medical skill and used by anesthetists for administering local anesthetics to the subarachnoid space. Prior knowledge of how far the needle needs to be inserted from skin to the subarachnoid space distance (SSD) has a paramount role to guide spinal needle placement and reduce complications related to lumbar puncture. Therefore, we aimed to determine the depth of spinal needle insertion and its associated factors among patients who underwent surgery under spinal anesthesia.

Methods: An institutional based cross-sectional study design was conducted among 274 patients who underwent surgery under spinal anesthesia. Following very successful lumbar puncture procedure, the distance from skin entry point to the tip of the spinal needle was measured. The data were entered into an Epi data version 4.3.1 and exported to SPSS software version 20 for analysis. Descriptive analysis, simple linear and multiple linear regression analysis were used. Then, in order to assess the correlation of depth of spinal needle insertion with other independent variables Pearson’s correlation coefficient (r) was applied.

Results: Two hundred seventy four patients comprising 112 (40.8%) male and 162 (59.1%) female were included in the study with a mean height, weight and body mass index (BMI) of 1.63 m, 62.9 kg, and 23.9 kg/m2 respectively. The mean distance from skin to the subarachnoid space was 5.13 ± 0.69 cm ranging from 3.5 to 7.1
cm. Pregnancy, weight and BMI had statistically significant effect on the mean SSD (p < 0.001, p < 0.001 and p = 0.014) respectively.

Conclusions: The distance from the skin to the subarachnoid space was differed among individuals. The SSD was affected by individuals’ pregnancy status, BMI and weight. Hence, to minimize complications, these factors should be taken into consideration at the time of spinal needle insertion.