The effect of body mass index on the spread of spinal block in patients with rheumatoid arthritis.

Purpose: Body mass index (BMI) has a significant effect on the spread of sensory spinal block in rheumatoid patients. We tried to achieve the same spread of spinal block for patients in three different BMI groups and, on the basis of the results from a preliminary study, used a simple method feasible for clinical practice. We hypothesized that BMI-related inverse dosing of plain bupivacaine according to low, normal, and high BMI would result in no difference in block extent.