THE DIRECTION OF THE WHITACRE NEEDLE APERTURE AFFECTS THE EXTENT AND DURATION OF ISOBARIC SPINAL-ANESTHESIA

The use of Whitacre spinal needles results in directional flow out of the needle aperture, diverting local anesthetic from the longitudinal axis of the needle. Thus, a change in orientation of the needle apertu re would be expected to result in a different local anesthetic distrib ution in the subarachnoid space. We studied 40 outpatients undergoing elective knee arthroscopy under spinal anesthesia with 60 mg plain lid ocaine 2% in a prospective, double-blinded manner. Patients were rando mly assigned to either Group I (needle aperture oriented in a cephalad direction throughout intrathecal injection) or Group II (aperture dir ected caudally). Onset and offset of sensory and motor block were anal yzed at frequent intervals. Times to completion of ambulatory mileston es, including discharge, were recorded. Group I was characterized by a higher sensory level (T 3.4 +/- 1.3 vs T 6.6 +/- 2.8, P < 0.001). Gro up I had significantly shorter duration of lumbar sensory anesthesia ( 149.2 +/- 30.6 min vs 177.8 +/- 23.5 min, P < 0.01) and motor blockade (117.6 +/- 26.1 min vs 150.0 +/- 22.8 min, P < 0.001). Mean time to o utpatient discharge was approximately 32 min shorter in Group I. The o rientation of the Whitacre needle aperture exerts a major influence on sensory level, as well as the duration of isobaric Lidocaine spinal a nesthesia.