When a routine procedure goes wrong Print E-mail
News - Rubrieke
Tuesday, 25 March 2014 12:28
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Dr Liesel van der Merwe is a small animal medicine specialist. Send her your questions: This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

Dr Liesel van der Merwe

No procedure is ever 100% without complications – that would be a perfect world. Unfortunately this also applies to anaesthesia in our pets. There is always a small risk of a complication, no matter how routine the procedure.

Studies in human medicine show anaesthetic-related deaths to occur in 0.01-0.019% of patients. In the UK a study has shown that anaesthetic-related deaths occurred in 0.063% of dogs and 0.062% of cats. This number includes all surgical procedures, including emergency trauma surgery where the patient is already high risk.

Routine procedures in veterinary science include sterilisations, dental procedures and the removal of small lumps and bumps. There are definite species and breed-related risks. Large breed dogs and some cats may have occult heart disease. A dilated heart with a weakened muscle is frequent in some canine breeds and may not show any clinical signs, whereas a very thick heart muscle may occur in cats. The use of anaesthetic drugs and intravenous fluids will result in a decompensation and development of heart failure while anaesthetised.  

Small breed dogs with a heart murmur, but no clinical disease, or well-managed early heart disease, are not at a greater risk than dogs without a heart murmur.

Brachycephalic dogs such as boxers and bulldogs have excessive folds of tissue in their throats which can flop down and obstruct breathing. This muscle relaxation can be exacerbated by certain sedatives, which are contra-indicated in these breeds.

Once an endotracheal tube is placed in these patients they actually breathe beautifully as their obstructive upper airway folds have been bypassed. The risk is when the endotracheal tube is removed and they are waking up. They need constant supervision until they are wide awake to check that the upper airway doesn’t close up or collapse.

Cats are at increased risk when they have to be entubated, as their larynxes and trachea are very sensitive and can go into a spasm and severely swell. For short procedures, an injectable anaesthetic is preferable. Inhalation anaesthesia is only used for long procedures. They are also very sensitive to too much intravenous fluids and may develop fluid in the lungs.

Smaller animals and thin older animals are at increased risk due to low body weight, which may result in relative anaesthetic overdose, and also their tendency to develop hypothermia during the procedure. Animals with hypothermia compensate poorly for decreased blood pressure and are inclined to develop shock more easily.

Not withholding food and water from the patient can result in vomiting and aspiration of gastric contents while under anaesthesia. Most of the anaesthetics and sedatives relax the junction of the stomach and oesophagus, causing reflux. The risk of aspiration is minimised if a cuffed endotracheal tube has been placed. 

Before you get so stressed that you never take your animal for a procedure again, you need to realise that veterinarians are aware of these risks. Improved patient monitoring by dedicated staff and newer monitoring devices decrease many of these complications.

There are few veterinary specialist anaesthetists and they would dramatically increase the cost of any procedure. Veterinarians sometimes operate and keep an eye on the anaesthetics at the same time with a technician or veterinary nurse assisting. This multitasking is facilitated by monitors connected to the patient, which beep every time the patient breathes, and check blood pressure and heart rate.

If a patient goes too deep under anaesthetic, the breathing slows down before the heart slows down and there is ample warning. Resuscitation of these patients is very successful, so this is a small cause of anaesthetic deaths.

In cats and smaller animals we use infusion pumps which can carefully regulate the amount of fluid they receive intravenously. This fluid can go through warmers or be wrapped around hot water bottles to counteract hyperthermia. Heating pads are also used in surgery to try to maintain body temperature, which is inclined to drop.

The newer anaesthetics are safe and there is a greater variety available for specific types of patients. Patients are put in a recovery ward where they are monitored before returning to the general ward.

If you are worried about the anaesthetic, ask your veterinarian what his systems and procedures are like to get peace of mind.


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