Complications and local anaesthetic toxicity in regional anaesthesia

Local anaesthetic agents are administered every day in clinical practice. These agents are relatively safe when administered in proper dosages at appropiate anatomical sites. However, when excessive dosages are administered or the incorrect site of administration is used there is a potential for toxic reactions. Ropivacaine, a pure S-enantiomer, and levobupivacaine, a single isomer of bupivacaine, have been introduced as new long-acting local anaesthetic agents with a potentially reduced toxicity compared with bupivacaine. The present review deals with recent knowledge about systemically induced local anaesthetic toxicity and localized toxicity.

Studies have compared cardiotoxicity directly between ropivacaine and levobupivacaine in intracoronary injection in sheep and pigs, in small mammals, and arrhythmias and resuscitation in dogs. Direct left coronary arterial infusions of local anaesthetics in a conscious sheep model precludes central nervous system actions. Intracoronary studies showed similar toxicity for levobupivacaine and ropivacaine. When comparing and interpreting in-vivo animal studies of local anaesthetic toxicity, species variations, differences in the mode and site of local anaesthetic administration, and whether the animal is under the influence of anaesthesia must all be considered. Stereoselectivity may play a role in the lengthening of the atrioventricular conduction time for bupivacaine. In-vitro studies have revealed that intracellular calcium concentrations may contribute to myotoxicity.

Current evidence suggests that ropivacaine is slightly less toxic than levobupivacaine; however, the difference in potency between the two agents is greater. The new local anaesthetic agents can be regarded as 'safer', but must not be regarded as safe.