Unilateral spinal anesthesia or combined sciatic-femoral nerve block for day-case knee arthroscopy. A prospective, randomized comparison.

BACKGROUND: To evaluate the time required to achieve surgical block and fulfill standardized discharge criteria in outpatients receiving knee arthroscopy with either unilateral spinal anesthesia or combined sciatic-femoral nerve block.

METHODS: After a standard midazolam/ketoprofen premedication and baseline measurement of cardiovascular parameters, 50 ASA physical status I-II patients scheduled for elective outpatient knee arthroscopy were randomized to receive unilateral spinal anesthesia with 8 mg of 0.5% hyperbaric bupivacaine injected without barbotage through a 25-gauge Whitacre spinal needle (group USA, n = 25), or combined sciatic-femoral nerve block with 25 ml of 2% mepivacaine (15 ml for femoral nerve block and 10 ml for sciatic nerve block) (group SFNB, n = 25). Times from local anesthetic injection to achievement of surgical block defined as the presence of adequate motor (complete motor blockade of the operated limb in the USA group and inability to move the ankle and the knee of the operated limb in the SFNB group) and sensory (loss of pinprick sensation at T12 on the operated side in the USA group, or in the femoral and sciatic nerves distribution in the SFNB group) blocks was recorded. Times to block resolution, urination, unassisted ambulation, and readiness to home discharge were also recorded by a blind observer, as well as occurrence of untoward events during surgery.

RESULTS: Surgical block was achieved in 15 +/- 6 min in group USA and 16 +/- 6 min in group SFNB (p = NS). No differences in hemodynamic undesired effects and success rate were observed. Even though USA patients showed a faster time to ambulation (166 +/- 44 min versus 217 +/- 49 min, p = 0.002) and later urination (240 +/- 90 min versus 145 +/- 36 min, p = 0.0001) than SFNB group, no differences in home discharging were reported (246 +/- 98 min versus 211 +/- 77 min, respectively). Bladder catheterization was required in 2 patients of USA group only; however, no patient was admitted to the hospital because of urinary retention.

CONCLUSIONS: In outpatient knee arthroscopy, a combined sciatic-femoral nerve block with 2% mepivacaine provides similarly successful anesthesia with onset times and home discharge similar to those provided by unilateral spinal anesthesia.