Relationship of abdominal circumference and trunk length with spinal anesthesia level in the term parturient

Background We hypothesized that body shape metrics influence the anatomy of spinal canal and intraabdominal pressure in three dimensions. We explored the effects of abdominal circumference, trunk length, and their combination on the level of spinal anesthesia in the term parturient in this study. Methods Thirty term parturients, ASA class I-II, from 20 to 41 years of age, scheduled for cesarean section were enrolled in this observational study. Abdominal circumference (AC) and trunk length (TL) were recorded preoperatively. Spinal anesthesia was performed with 10 mg 0.5 % hyperbaric bupivacaine at the L4-L5 intervertebral space in all parturients. Correlation between maximal sensory spinal anesthesia level and physical parameters was analyzed with Spearman rank correlation coefficients. The calculated r value was compared with r = 0 with p < 0.05 as the significant level. The prediction power of these physical parameters for spinal level was evaluated by prediction probability. Results The parameter TL/AC(2) was statistically correlated with maximal sensory level (Spearman correlation coefficient, -0.45 with p < 0.02). The prediction probability of TL/AC(2) for the dermatomal level was P-K = 0.685. If the dermatomal levels were lumped as higher (above T2) and lower (below T3) levels, the prediction probability of TL/AC(2) was as high as P-K = 0.856. Conclusions TL/AC(2), which simulated the ratio of the long axis and transection area of the abdomen, was correlated with maximal spinal level, and parturients with low TL/AC(2) values tended to have higher dermatomal levels during spinal anesthesia.