Do patient variables influence the subarachnoid spread of hyperbaric lidocaine in the postpartum patient?

Age, height, weight, body mass index (weight/height2), and vertebral column length may affect the subarachnoid spread of local anesthetics. Little information exists concerning the relationship between these variables and the spread of hyperbaric lidocaine. The authors studied the influence of patient demographics on the block produced by hyperbaric lidocaine in women undergoing postpartum tubal ligation.

Within 48 hours of vaginal delivery, the authors studied 44 ASA class 1-2 women agreeing to spinal anesthesia for postpartum tubal ligation. Before induction of anesthesia, the authors weighed each patient, measured her height and vertebral column length, and calculated body mass index. In a standardized manner, the authors induced spinal anesthesia with 5% lidocaine 75 mg. An observer, blinded to the measured variables, evaluated loss-of-temperature sensation and loss-of-sensation of sharpness to pinprick bilaterally every 5 minutes for 30 minutes and again at 45 and 60 minutes.

There was no correlation between age, weight, body mass index, vertebral column length, or time from delivery to placement of the block, and the spread of sensory block after subarachnoid injection of hyperbaric lidocaine. Only height weakly correlated with the spread of block (r2 = 0.15).

While height may have some small influence on the spread of sensory block, the variation in spread of block within patients of the same height is large. The data suggest that adjusting the dose of local anesthetic injected based on differences in patient height would provide no clinically significant benefit.