Level of spinal anesthesia can be predicted by the cerebrospinal fluid pressure difference between full-flexed and non-full-flexed lateral position.

We studied whether cerebrospinal fluid pressure difference between full-flexed and non-full-flexed lateral position (dP) influences the spread of intrathecally (i.e., spinal) administered anesthetic solution (SSA). Forty-two women, 18-60 yr old, who underwent gynecologic surgery under spinal anesthesia were enrolled in the study. They were divided into two groups (group 1: less than 40 yr old, group 2: greater than or equal to 40 yr old). Before spinal anesthetic injection, we measured the pressure difference produced by postural change from the right lateral decubitus position (non-full-flexed) for needle insertion at the L2-3 interspace to a full-flexed lateral decubitus position with a spinal needle in place. After they returned to the non-full-flexed lateral position, 14 mg of plain tetracaine in 10% dextrose solution (2.8 mL) was injected intrathecally in each patient. Pressure differences had a significant correlation with the cephalad levels of spinal anesthesia in each group; the larger pressure difference was associated with a larger SSA. The relationship was stronger in the younger group (correlation coefficients, 0.82 and 0.63; P-values less than 0.01 in groups 1 and 2, respectively). Three patients in group 1 developed T-2 anesthesia, whereas no one in group 2 did (P less than 0.01), and their pressure difference values ranged from 12 to 16 cm H2O, substantially larger than those of the other patients in group 1. Five patients in group 2 developed T-3 anesthesia, whereas no patient in group 1 (P less than 0.01) did, and their pressure differences were not essentially larger than those of the rest in the same group. The authors conclude that pressure differences correlated with the SSA, although the mechanism remains to be clarified. It seems possible to predict which patient in the younger patient group may develop unintentional high spinal anesthesia (T-3 or higher) by measuring pressure differences.