[Does the mixture of bupivacaine and prilocaine as opposed to bupivacaine afford a clinical advantage in epidural anesthesia?].

Local anaesthetic mixtures are often used to shorten the onset of regional anaesthesia. However, the results of these mixtures of epidural anaesthesia (EDA) are controversial. Alkalinisation of bupivacaine shortens the onset of EDA. Since mixing prilocaine with bupivacaine results in a local anaesthetic mixture with a pH of 6.8, we investigated whether this mixture can shorten the onset of EDA compared to plain bupivacaine. METHOD. In a randomised, double-blind study, 60 patients received single-shot EDA with a standardised amount of local anaesthetic (1 ml/segment for 150 cm body height +0.1 ml/segment for each further 5 cm). Group A received plain bupivacaine 0.5%, group B bupivacaine 0.5% and prilocaine 2% in a 1:1 ratio. Sensory (loss of warm/cold and pinprick sensation) and motor blockade (modified Bromage score) were studied 5, 10, 15, 20, 30, and 40 min after injection of the local anaesthetic. RESULTS. There was no difference in the onset of sensory blockade: loss of warm/cold and pinprick sensation developed in the same manner in both groups. Ten minutes after injection all patients showed changes in the perception of warm and cold stimuli. In group A this ranged from T 8.1 +/- 2.14 to L 4.36 +/- 1.79 and in group B from T 8.8 +/- 2.0 to L 4.4 +/- 1.55. Forty minutes after injection loss of warm/cold sensation ranged from T 6.6 +/- 2.89 to L 5.4 +/- 1.42 in group B and from T 7.2 +/- 1.24 to L 5.7 +/- 0.88 in group A. Nearly the same results were obtained for the pinprick test. Motor blockade developed more rapidly and intensely in group B. At the end of the observation period there were still 5 patients without any motor blockade in group A, while all patients in group B showed signs of motor blockade. DISCUSSION. Shortening of the onset times has been observed when alkalinized local anaesthetic solutions with a pH above 7.0 are used for EDA. In the present study the mixture of prilocaine and bupivacaine did not shorten the onset of EDA, most likely because the pH of this mixture is only 6.8. In contrast to peripheral nerve blocks, mixtures of local anaesthetics for EDA do not offer a clinical advantage with respect to onset time compared to plain local anaesthetics.