Dosage finding for low-dose spinal anaesthesia using hyperbaric prilocaine in patients undergoing perianal outpatient surgery.

BACKGROUND Hyperbaric prilocaine 20 mg/ml may be preferable for perianal outpatient surgery. The aim of this prospective, single-centre, randomised, single-blinded, controlled clinical trial was to determine the optimal dosage of hyperbaric prilocaine 20 mg/ml for a spinal anaesthesia (SPA) in patients undergoing perianal outpatient surgery. METHODS One hundred and twenty patients (18-80 years/American Society of Anesthesiologists grade I-III) were enrolled in this study. The patients were randomised to receive 10, 20 or 30 mg of prilocaine for SPA. We measured expansion of the sensory and motor block, evaluated times to walk, void and being eligible for discharge, and determined the demand of analgesics. RESULTS 116/120 patients were available for analysis. The expansion of the sensory block gained with an increasing dosage: 10 mg: 3(1-6) dermatomes; 20 mg: 4(2-6) dermatomes; 30 mg: 5(3-7) dermatomes (P < 0.0001). Dermatomes were counted upwards beginning with S(5). Also, the motor block gained with an increased dosage (Bromage score 1-3: 10 mg: n = 3, 20 mg: n = 8 and 30 mg: n = 18, P = 0.0002). Patients receiving 10 mg were ready for discharge earlier compared with both other groups (10 mg: 199 ± 39 min; 20 mg: 219 ± 47 min; 30 mg: 229 ± 32 min, P = 0.0039). Pain occurred earlier in the 10 mg group than in the 30 mg group (10 mg: 168 ± 36 min; 30 mg: 205 ± 33 min, P = 0.0427). The demand of additional analgesics was comparable in all dosage groups. CONCLUSION Hyperbaric prilocaine 20 mg/ml can be applied in dosages of 10, 20 and 30 mg for SPA in perianal surgery. Because of sufficient analgesia, missing motor block and shorter recovery times, 10 mg of hyperbaric prilocaine 20 mg/ml can be recommended for perianal outpatient surgery.