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-lastinganalgesia after deflation of the tourniquet cuff, with fewerside-effects, than lidocaine 5 mg ml^–1 (0.5%) after i.v.regional anaesthesia (IVRA). Whether ropivacaine 2 mg ml^–1also exerts this advantage over prilocaine 5 mg ml^–1,the local anaesthetic of choice in IVRA in most European countrieswas investigated in this study. Methods. Sixty outpatients scheduled for forearm or hand surgeryreceived IVRA with 40 ml of ropivacaine 2 mg ml^–1 (Ropi)or prilocaine 5 mg ml^–1 (Prilo) in a randomized, double-blindedfashion. The development and recovery of pin-prick analgesiaand motor power of the hand, as well as ropivacaine and prilocaineplasma concentrations (n=30), were assessed during and afteroperation. Results. Anaesthesia for surgery was adequate in both groups.Pin-prick analgesia was achieved at a similar rate, except inthe radial nerve distribution area where at 10 min 60% of Ropiand 90% of Prilo patients had analgesia (P=0.017). At 10 min100 and 97% had motor block of the hand in the Ropi and Prilogroups, respectively. Recovery of the sensory block in all innervationareas was already observed 2 min after the tourniquet cuff release.At 10 min after releasing the tourniquet cuff 31% of the Ropipatients and none of the Prilo patients still had analgesiain the median nerve distribution (P=0.004). At 12 min, 42% inthe Ropi group and none in the Prilo group had decreased gripstrength. After the release of the tourniquet, mean plasma concentrationsof ropivacaine were higher than those of prilocaine. The highestindividual concentration of ropivacaine was 1.65 µg ml^–1and that of prilocaine 0.6 µg ml^–1. None of theRopi patients experienced any symptoms of local anaesthetictoxicity. Conclusions. Compared with prilocaine 5 mg ml^–1, analgesiain IVRA with ropivacaine 2 mg ml^–1 developed slightlymore slowly, while motor block developed at a similar rate.After the release of the tourniquet, sensation recovered quicklyand at a similar rate in the two groups, except for a slightlyslower recovery after ropivacaine in the innervation area ofthe median nerve, but no surgically useful extended analgesiaafter the cuff deflation was observed. Despite a 60% lower milligram-dose,ropivacaine plasma concentrations were markedly higher thanthose of prilocaine.