Local Anaesthetics and Nerve Conduction


Local Anaesthetics

The World Federation of Societies of Anaesthesiologists have this excellent article on “The Pharmacology of Local Anaesthetic Agents” as part of “Update in Anaesthesia”, a journal for anaesthetists in developing countries. They also have this page on local anaesthetic toxicity. See alsoWikipedia, Anaesthetist.com, FRCA site and E-Medicine.

See also a related chapter on Local and Regional Anaesthetic Techniques.


Bupivacaine has been widely used as a long-lasting amide local anaesthetic. Adrenaline improves duration of block by say 30-50% (the effect is less obvious than for lignocaine). The most feared toxicity is prolonged cardiac arrest which may occur before convulsions commence. CPR should be maintained for at least an hour. Adrenaline +/- vasopressin are important during CPR to maintain blood pressure. Adrenaline may worsen the arrythmias Insuling/Glucose/K, clonidine and lipid have been suggested as adjunctive therapy. See Weinberg 2002.

Overview from Wikipedia.

The levo (S) enantiomer of bupivacaine is less cardiotoxic but provides similar analgesia than the racemic mixture. The additional margin of safety may be 25% to 40% with risk of cardiotoxicity bupivacaine > L-bupivacaine > ropivacaine. See Royse 2005.


The original amide local anaesthetic. Information from Wikipedia, History Holmdahl 1998.


Information from Wikipedia.


Only the s-racemate was marketed; it should result in less chance of cardiac arrest than bupivacaine following overdose or IV administration but otherwise be clinically similar. See also this paper by Morrison 2000. A detailed meta-analysis of its use in labour suggests that any clinical differences are minor.

Pharmacology: Wikipedia, RxList: physical properties and kinetics.


EMLA is a eutectic mixture of 2.5% each lignocaine and prilocaine. Topical application provides good superficial skin anaesthesia. Information from Medicines.org.au

LMX is a 4% lignocaine only micro formulation. Works maybe a little more quickly than EMLA with less blanching. Also Topicaine. See this excellent review of the newer topical local anaesthetics by Friedman.

Nerve Conduction

Ritchi Song’s web page on nerve conduction is great. This paper explains how nodes of ranvier and myelination is helpful (the depolarisation jumps at the speed of light from one node of ranvier to the next).

Leave a Reply

Your email address will not be published. Required fields are marked *