Selective sensory spinal anaesthesia with hypobaric lidocaine for anorectal surgery

Lidocaine has been used for spinal anaesthesia since 1948, seemingly without causing concern until recently. This study aimed at evaluating the feasibility of performing anorectal surgery in outpatient settings with low hypobaric lidocaine doses.

Three groups of 50 patients, physical status ASA I-II, undergoing anorectal surgical procedures in a prone jack-knife position, received 3 ml (18 mg), 4 ml (24 mg) or 5 ml (30 mg) of hypobaric 0.6% lidocaine. Sensory and motor blockade, time until first urination, ambulation, complications and the need for analgesics were evaluated. Patients were followed until the third post-operative day.

Adequate sensory block was obtained in all patients. Blockade was significantly lower in Group 1. The level at 15 min was L(1) with 3 ml, T(11) with 4 ml and T(10) with 5 ml. Only 24 patients presented a moderate motor block. There was no hypotension, nausea or vomiting, urine retention, transitory neurological symptom or post-dural puncture headache in any patients. There was one case of bradycardia with 4 ml and two cases with 5 ml.

Hypobaric lidocaine predominantly provided a sensory block after injection in the prone jack-knife position. The smallest dose (3 ml=18 mg) provides sufficient analgesia with a lesser dispersion and a shorter duration. The major advantages were haemodynamic stability and a high degree of patient satisfaction.