A general anaesthetic is one of the key tools of a veterinary surgeon. So many anaesthetics are carried out in a typical vet clinic that it is easy to take the procedure for granted.
Two types of drugs are used in anaesthesia: one drug to “knock out” the animal , and the other to “maintain the anaesthesia”.
Induction of anaesthesia
The first drug is given by injection. This causes the animal to smoothly lapse into a safe level of unconsciousness, but the effect usually only lasts for a few minutes.
Maintenance of anaesthesia
This is enough time for a rubber or plastic tube to be introduced, through the mouth, into the windpipe. The tube is connected to an anaesthetic machine which provides a controlled concentration of the second drug, which is an anaesthetic gas. This ensures that the animal remains at the ideal stage of unconsciousness.
Newer drugs have made anaesthesia far safer
Both types of anaesthetic drugs have been much improved in the past thirty years. Earlier versions were relatively toxic. There was a significant risk, especially in old or weakened animals. Even healthy animals suffered a slow recovery and a ‘hangover’.
The latest drugs are ultra-short acting and very safe. In the past, some “high-risk” cases could take several hours to recover from a short anaesthetic. In contrast, I recently saw a twenty-year-old cat recovering so rapidly that he was looking for his dinner within fifteen minutes of waking up.
Anaesthetic monitoring is essential
Anaesthetic monitoring has also improved. A general anaesthetic does not just cause the brain to lapse into unconsciousness. There are other effects on many body systems, and the changes are often not visible to the naked eye. Monitoring equipment allows anaesthetists to identify the earliest, most subtle changes in essential organs such as the heart and the respiratory systems. It is then possible to take rapid corrective action before it is too late.
The new drugs and the improvements in monitoring mean that vets can now safely anaesthetise animals that would formerly have been considered too risky, including geriatric pets and patients with serious illness.
A case study: anaesthetising a guinea pig
Traditionally, guinea pigs have been high-risk anaesthetic patients. Gertie had a broken leg, She was a wriggly, active little creature, and anaesthesia was needed to allow the X-ray to be taken.
Gertie’s veins were so small that it was not possible to give her the usual injection of induction agent. Instead, she was anaesthetised using a mask with a safe, odourless gas. When she was asleep, the mask was kept over her face, and the gas concentration was reduced to a safe maintenance level. A monitoring probe was attached to her right front paw, and this gave a continual display of the oxygen level in her blood. At the first hint of a problem, we would have been able to step in to assist her. Tiny creatures like guinea pigs are very susceptible to chilling during anaesthesia. Gertie was placed on a sheet of plastic “bubble-wrap” to keep her warm and she was returned to a warm bed as soon as we had finished.
The X-rays showed that Gertie had a “good” fracture. No operation or plaster cast was needed. The broken leg would heal by itself. Gertie recovered from the anaesthetic within ten minutes, and was nibbling hay soon afterwards.
General anaesthesia is very similar for all animals, from guinea pigs to Great Danes. The gas used to keep Gertie comfortably asleep is used for all animals, regardless of size. The same monitoring probe that was attached to Gertie’s leg would be placed on the tip of the tongue of a Great Dane.
I could not do my job as a vet without the help of safe general anaesthesia for my patients.
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