Comparison of ropivacaine 2 mg ml-1 and prilocaine 5 mg ml-1 for i.v. regional anaesthesia in outpatient surgery

Background. Ropivacaine 2 mg ml(-1) (0.2%) provides longer-lasting analgesia after deflation of the tourniquet cuff, with fewer side-effects, than lidocaine 5 mg ml(-1) (0.5%) after i.v. regional anaesthesia (IVRA). Whether ropivacaine 2 mg ml(-1) also exerts this advantage over prilocaine 5 mg ml(-1), the local anaesthetic of choice in IVRA in most European countries was investigated in this study. Methods. Sixty outpatients scheduled for forearm or hand surgery received IVRA with 40 ml of ropivacaine 2 mg ml(-1) (Ropi) or prilocaine 5 mg ml(-1) (Prilo) in a randomized, double-blinded fashion. The development and recovery of pin-prick analgesia and motor power of the hand, as well as ropivacaine and prilocaine plasma concentrations (n=30), were assessed during and after operation. Results. Anaesthesia for surgery was adequate in both groups. Pin-prick analgesia was achieved at a similar rate, except in the radial nerve distribution area where at 10 min 60% of Ropi and 90% of Prilo patients had analgesia (P=0.017). At 10 min 100 and 97% had motor block of the hand in the Ropi and Prilo groups, respectively. Recovery of the sensory block in all innervation areas was already observed 2 min after the tourniquet cuff release. At 10 min after releasing the tourniquet cuff 31% of the Ropi patients and none of the Prilo patients still had analgesia in the median nerve distribution (P=0.004). At 12 min, 42% in the Ropi group and none in the Prilo group had decreased grip strength. After the release of the tourniquet, mean plasma concentrations of ropivacaine were higher than those of prilocaine. The highest individual concentration of ropivacaine was 1.65 mu g ml(-1) and that of prilocaine 0.6 mu g ml(-1). None of the Ropi patients experienced any symptoms of local anaesthetic toxicity. Conclusions. Compared with prilocaine 5 mg ml(-1), analgesia in IVRA with ropivacaine 2 mg ml(-1) developed slightly more slowly, while motor block developed at a similar rate. After the release of the tourniquet, sensation recovered quickly and at a similar rate in the two groups, except for a slightly slower recovery after ropivacaine in the innervation area of the median nerve, but no surgically useful extended analgesia after the cuff deflation was observed. Despite a 60% lower milligram-dose, ropivacaine plasma concentrations were markedly higher than those of prilocaine.