[Paresthesia and spinal anesthesia for cesarean section: comparison of patient positioning]

To determine the incidence of paresthesia during lumbar puncture performed with the patient in different positions.

A single-blind prospective study of patients scheduled for elective cesarean section, randomized to 3 groups. In group 1 patients were seated in the direction of the long axis of the table, with heels resting on the table. In group 2 they were seated perpendicular to the long axis of the table, with legs hanging from the table. In group 3 they were in left lateral decubitus position. Lumbar punctures were performed with a 27-gauge Whitacre needle.

One hundred sixty-eight patients (56 per group) were enrolled. Paresthesia occurred most often in group 3 (P = .009). We observed no differences in blood pressure after patients moved from decubitus position to the assigned position. Nor did we observe between-group differences in blood pressure according to position taken during puncture.

Puncture undertaken with the patient seated, heels on the table and knees slightly bent, is associated with a lower incidence of paresthesia than puncture performed with the patient seated, legs hanging from the table. Placing the patient's heels on the table requires hip flexion and leads to anterior displacement of nerve roots in the dural sac. Such displacement would increase the nerve-free zone on the posterior side of the sac, thereby decreasing the likelihood of paresthesia during lumbar puncture. A left lateral decubitus position would increase the likelihood of paresthesia, possibly because the anesthetist may inadvertently not follow the medial line when inserting the needle.