Local issues

Many surgical procedures that involve a horse's head can be carried out under local anaesthetic, to the benefit of both horse and vet. Liz Richardson MRCVS explains

- Liz Richardson and Peter Green

LOCAL anaesthetic techniques are valuable adjuncts to sedation and systemic analgesia (whole-body pain relief without loss of consciousness), facilitating diagnostic procedures and any surgery needed in standing, conscious horses.

These techniques are useful for providing pain relief to perform surgery, to minimise movement, and for postoperative analgesia.

They are used for:

• ocular examination
• eye surgery
• facial wound repairs
• dental extractions
• periodontal (gum) treatments
• jaw fracture repairs
• sinus procedures

THE MEDICATION 

LOCAL anaesthesia involves injection of a local anaesthetic medication into tissue surrounding specific nerves (perineural infiltration). These anaesthetics are designed to penetrate nerves and interrupt (or “block”) nerve conduction, resulting in reversible anaesthesia for a predictable period of time.

Perineural infiltration with local anaesthetic can block nerves of sensation, resulting in numbness of a specific area. Motor nerves can also be blocked, preventing movement. Blocking transmission of information along nerves can therefore allow for desensitisation or paralysis of various structures, and so enable veterinary procedures to be performed safely, humanely, and effectively.

Vets select appropriate local anaesthetics to use for head blocks, which will often be one that offers a relatively fast onset of action, short duration and safety profile. Toxicity and side effects of local anaesthetics can occur if enough of the medication is absorbed into the blood, and toxic effects of the nervous and cardiovascular systems are possible. A short duration of action of the local anaesthetic used will tend to mean low possible toxicity.