Spinal anaesthesia for ambulatory arthroscopic surgery of the knee: a comparison of low-dose prilocaine and fentanyl with bupivacaine and fentanyl

Background. Prospective data on the use of prilocaine for ambulatory spinal anaesthesia remain limited. We compared the behaviour and characteristics of subarachnoid block using prilocaine and fentanyl with that of bupivacaine and fentanyl. Methods. In a prospective, double-blind, randomized controlled trial, 50 patients undergoing elective ambulatory arthroscopic knee surgery received subarachnoid anaesthesia, with either prilocaine 20 mg and fentanyl 20 mg (Group P) or plain bupivacaine 7.5 mg and fentanyl 20 mg (Group B). Primary endpoints included times for onset of maximum sensory block level and regression of sensory block to L4, and also motor block at 1 and 2 h, and levels of haemodynamic stability. Comparisons between the groups were made by chi(2) test for proportions and the Mann-Whitney test for ordinal data. Time-to-event data were analysed by the Mann-Whitney test for uncensored data or the logrank test for censored data. Results. At 2 h, motor block in Group P had fully resolved in 86% of patients, compared with 27% in Group B (P<0.001). Median time to regression of sensory block to L4 was significantly shorter in Group P (97 min) than in Group B (280 min) (P<0.001). A clinically significant decrease in arterial pressure was more common in Group B (73%) than in Group P (32%) (P=0.004). Two patients in Group P required conversion to general anaesthesia, but for reasons unrelated to prilocaine itself. Conclusions. The combination of prilocaine and fentanyl is a better alternative to that of low-dose bupivacaine and fentanyl, for spinal anaesthesia in ambulatory arthroscopic knee surgery.