Contents

• Local Anaesthetics
  • Bupivacaine
  • Lignocaine
  • Mepivacaine
  • Ropivacaine
  • EMLA
• 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 also Wikipedia, Anaesthetist.com, FRCA site and E-Medicine.

Allan Palmer has set up a slide show on Local Anaesthetics. It includes some very clear images but can be slow to download.

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

Bupivacaine

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. More detail from drugs.com.

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.

Lignocaine

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

Mepivacaine

Information from Astra Wikipedia.

Ropivacaine

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 s of its use in labour suggests that any clinical differences are minor. This paper from Washington University provides a concise summary.

Pharmacology: Wikipedia, RxList: physical properties and kinetics. Ropivacaine in obstetric anaesthesia by Stephen Gatt. Also experience with ropivacaine for labour analgesia by Genevieve Goulding, all from Manbit, from about 1995. Brief summary from Astra.

EMLA

Eutectic mixture of local anaesthetics. Topical application provides good superficial skin anaesthesia. Information from the Astra-Zeneca site

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). For a more detailed explanation see this page.