Anaestheia - How Safe is it?

The fact is, anaesthesia is as dangerous or as safe as your animal hospital makes it.  All anaesthesia contains risks.  Anaesthesia is defined as a state of controlled and and reversible unconsciousness characterized by a lack of pain sensation and a lack of memory, and relatively depressed reflex responses.  Ideally, it is the goal of the veterinarian and technician to achieve this with minimal affect on your pets vital systems, particularly circulation and respiration.  There are a series of steps your veterinarian and technician will take to ensure your pet’s anaesthetic goes as smooth and safe as possible.

Microscopic evaluation of blood

Typical red blood cells at100X

The first step is a thorough history from you, the client.  Your veterinarian needs to know how your pet has been doing at home.  Any signs of illness like coughing, sneezing, vomiting or diarrhea?  Has there been an increase in water consumption?  Any changes in behaviour?  Any relevant travel history?  Does your pet have a history of any medical problems?  Is your pet on any current medications or supplements?  Answers to these questions may give your veterinarian insight as to whether your pet is at risk for an illness or disease process that may affect his/her reaction to anaesthetic drugs.

The next step is a thorough physical examination by the veterinarian.  The vet will take your pets temperature, palpate his/her internal organs, assess hydration and evaluate his/her circulatory and respiratory systems.  This will further help the veterinarian assess health. 

Pre-anaesthetic blood work is the next vital step in creating a safe anaesthetic.  Blood chemistry helps the veterinarian determine the health of your pets liver and kidneys.  These two organs are very important in the metabolism and excretion of anaesthetic drugs from your pet’s body.  If they are not functioning properly your pet may suffer an overdose of medication and have difficulty waking up from anaesthesia.  As part of pre-anaesthetic testing, a complete blood count will also be run.  This will determine how well your pet moves oxygen around his/her body.  It will also tell us if there are signs of inflammation/infection or if your pet’s immune system is not functioning properly.  Most important for patients undergoing a surgery is a platelet count.  If platelets are low the patient may not be able to clot properly and may bleed during surgery. Sometimes, if certain blood values come back out-of-range, further testing may be required (ie a urinalysis) before an anaesthetic can proceed.  Knowing all of this allows the veterinarian to determine the safest drug protocol for your pet. 

The drug protocol should be chosen by the veterinarian with specific regard for the individual patient.  Any drug administered incorrectly can have adverse effects.  The veterinarian will determine the dose and route of each drug bearing in mind the findings of the patient history, the physical exam and the laboratory testing.

One of our basic gas anaestheia machines

“Balanced anaesthesia” should be used whenever possible.  This means that more than one drug is used to induce and maintain anaesthesia.  First a patient is given a “pre-med” to relieve anxiety and provide pre-emptive pain control.  This may make the patient drowsy but is not yet considered “general anaesthesia”.  Then the patient is induced with an induction agent which will put them under enough to allow a breathing tube to be placed in their airway.  “Intubation” allows the technician to control the patient’s airway and breathe for the patient if necessary.  It also protects the patient from aspirating fluids (blood, water, stomach contents), and allows the delivery of oxygen and anaesthetic gas.  The patient is then maintained on anaesthetic gas for the remainder of the procedure until recovery.  “Balanced anaesthesia” means that lower doses of each drug can be used minimizing the side effects of each drug. 

Rarely, some drugs can cause adverse effects in patients even when administered correctly.  It is impossible to predict which animals will react adversely to a drug that they have never had before.  Because of this is it very important to monitor anaesthetic patients closely and have an intravenous catheter in place.

If a problem arises, it is vital that the vet and technician be able to administer life saving drugs immediately.  The fastest route for these drugs is intravenously.  Unfortunately, trying to get IV access on a patient that is having a reaction (and probably has very low blood pressure) is difficult at best.  That is why an IV catheter should always be placed BEFORE anaesthesia is administered.  IV fluids can be used to increase blood pressure and provide a very fast way to administer emergency drugs.  If necessary we can also administer blood and blood products through the IV if the patient is bleeding.

All patients should have a dedicated technician monitoring them from pre-med to recovery.  While the patient is under general anaesthesia they should have their blood pressure, heart rate, respiratory rate and depth, and temperature checked regularly  and recorded on an anaesthetic record.  Trends in these values allow the veterinarian and technician to determine anaesthetic depth and adjust the amount of anaesthetic gas required to maintain a surgical plane of anaesthesia.  It is this close attention to trends in your pet’s vital signs that will alert the vet and technician that a patient is not doing well.  Early detection of an adverse reaction allows the vet and tech to correct the situation before it actually becomes a problem.  This level of monitoring should extend into the post operative recovery period.

Meghan
Reg. AHT