Tuesday, May 13, 2014

Anaesthesia and pets

Dixie with her collection of toys.

Last week I put together an article about the late Dr Martin Pearson, a veterinary anaesthetist who was tragically killed in a hit-and-run incident on Anzac Day. The driver remains at large. Its a really sad, abrupt end to the life of someone who clearly put his heart and soul into the profession. Hopefully the person involved in the accident will come forward and Dr Pearson's family can get some closure.

In talking to former colleagues and reading about Dr Pearson's career I learned that he had much to do with the registration of alfaxan CD, an anaesthetic agent used commonly in dogs and cats. Compared to many other agents it has a very high safety margin and is widely used in Australia. That and his many other achievements are a very special legacy.

On the topic of anaesthesia, one question pet owners often ask is what is the risk of anaesthetic death? Fortunately these are very rare.

It depends mostly on the underlying health of the patient at the time. We talk about ASA scoring, which is essentially providing a health score to patients - ASA I refers to healthy animals that are admitted for elective surgery (e.g. desexing), right up to ASA V which is a severely unwell, moribund animal. Why would anyone anaesthetise such a patient? The point is to avoid it where possible, but often its the only chance we have of saving them.

Dr Thierry Beths presented an excellent webinar last night for the ASAVA on anaesthesia of compromised patients. He reminded us that:
  • Animals undergoing emergency procedures were 1.6x more likely to die (Brodbelt 2007) - mostly because emergency procedures are carried out in compromised patients because they cannot be delayed.
  • An increased ASA score is associated with increased mortality. So in one study, dogs with an ASA score of I or II had a 0.05% risk of anaesthetic death, while those with a score of III-V had a 1.33% of death (Brodbelt 2008) - more than double. The numbers are very low, but the impact on the animal (and owner) is devastating of course.
  • Most anaesthetic deaths occur in the recovery period - usually within three hours of recovery. Dr Beths said this may be due to removal of monitoring equipment. Other factors such as hypothermia can play a role.

Many anaesthetic complications can be avoided simply by chosing drugs carefully, monitoring the patient and taking standard precautions (fasting patients prior to surgery, providing intravenous fluids where required, maintaining the airway, minimising anaesthetic time etc.) and anaesthesia in companion animal practice is generally very safe.