Premedication is a integral part of any anaesthetic protocol; it involves the administration of specific drugs that have been selected to use prior to induction, and which form part of an overall anaesthetic protocol. The reasons for premedicating patients are as follows:
Minimise stress and anxiety. Sedative and anti-anxiolytic effects of the drugs used will calm the patient, making them easier to handle and avoid unnecessary raised levels of catecholamines. This results in a safer environment for both patient and staff.
Reduce the dose of induction and maintenance agents. This is a key feature of premedication drugs. By lowering the amount of anaesthetic drug needed, this reduces the likelihood of adverse side effects on major body systems such as the cardiovascular and respiratory systems.
Promote a smooth induction of anaesthesia.
Reduction of muscle tone which is helpful during surgery.
Contribute to pre-emptive analgesia. By administering pain relief before a painful stimulus is experienced, it reduces the patient's response to pain and enables it to be more controlled. This will be explored further in the analgesia section.
Promote a smooth recovery. Many drugs will last into the post-operative period. This helps promote a calm recovery which is beneficial for both patient and staff.
There a variety of drugs that are suitable for use as premedicants.
In general, a drug with sedative properties is combined with an opioid analgesic; by adding an opioid, the dose of sedative required is lowered (this is referred to as 'synergism'). In addition, analgesia is also provided by the opioid drug.
There are various options for premedication and only a selection are discussed here. For the purposes of routine spay-neuter surgeries, the following combinations are commonly used used:
- Alpha-2 agonists/opioid mixtures: this combination is used at our ITC clinics.
- ACP/opioid mixtures
- Benzodiazepine/opioid mixtures
At our ITCs we use a combination of xylazine, with the addition of buprenorphine.
Prior to administering premedication, the patient should be receive a full clinical examination, and anaesthetic risk assessment. An accurate bodyweight is required (where possible) to ensure the correct dose of medication is given.