The Relationship Between Patients’ Anthropometric Characteristics and Depth of Spinal Needle Insertion

Many surgeries are performed under spinal anesthesia. Inexperienced practitioners may find it difficult to obtain subarachnoid access. This study aimed to examine the relationship between patients’ anthropometric characteristics and depth of spinal needle insertion to the subarachnoid cavity. 385 patients with ASA class I – II, aged 18 - 65 years and undergoing elective surgery of the lower abdomen and extremities under spinal anesthesia, were selected for this cross-sectional study. The patients’ demographic characteristics, body mass index (BMI), and anthropometric characteristics (height, weight, waist circumference, and arm circumference) were recorded. Linear regression and t-student tests were used to study the relationship between anthropometric characteristics and BMI, and depth of needle insertion. Of the 385 patients studied, 88 were female and 297 were male. There was a strong correlation between the depth of needle insertion and BMI (24.9 ± 3.9), and between depth and weight/height ratio (r = 0.95 and r = 0.92, respectively). There was no significant correlation between depth of needle insertion and weight, height, gender, or arm circumference, when considered separately. The statistical predicting models showed that the following relationship was observed between the needle depth and the weight/height ratio: A: needle depth = 0.69 + (10.1 × weight/height); B: needle depth = 0.56 + (0.18 × BMI). The results of this study show that there is a strong relationship between depth of needle insertion and BMI, and between depth and the weight/height ratio; appropriate depths can be determined according to the equations obtained.