Anaesthesia

What is Anaesthesia?

Anaesthesia is the process where we use various chemicals to create a state where and animal won't experience any pain. This can be in 2 forms, local and general anaesthesia. In local anaesthesia just the area which is to be operated on is infiltrated with local anaesthetic to temporarily deaden the nerve fibre and block pain. This is what dentist generally do when doing fillings. Unfortunately with local anaesthesia the patient can still move around so this limits its applications in veterinary medicine. The more common anesthesia used is general anaesthesia where drugs are given which depress the central nervous system blocking pain and essentially putting the patient into a deep, sensory free state of sleep.

Is it safe?

General anaesthesia in veterinary medicine is a very safe procedure in the vast majority of animals. Certain medical conditions mean that a different anaesthetic drug combinations be used. Generally when anaesthesia is being considered the risks of not treating the condition easily outweigh any risks associated with anaesthesia. These risk factors will be decided upon by your veterinarian based on clinical exam and any blood testing. As with in people, there are always some individuals who have undiagnosed underlying conditions which can increase the risks. This is one reason why we recommend pre-anaesthetic blood screening to identify any possible risk factors so they can be taken care of and their effect minimized. Your veterinarian should always discuss with you any possible risk factors and what they mean for your pet.

Why must I not feed my pet before anaesthesia?

It is very important that animals have an empty stomach when they are being anasthetised. This is because when they are anaesthetised they have no swallowing reflexes so if food were in the stomach it could possibly regurgitate and then pass down into the lungs which causes a very nasty form of pneumonia called aspiration pneumonia. Animals are much more likely to vomit while recovering anaesthesia if they have food in the stomach. There are times when we are unable to delay surgery after an animal has eaten such as after being hit by a car. In these cases we take extra precautions such as leaving its endotracheal tube in for as long as possible. We still however prefer to avoid the situation occurring where at all possible. Ideally one should withhold solid food for 12 hours prior to surgery and liquids about 8 hours. We usually tell our clients "No food after 7pm and no water after 11pm" if surgery is the next day.

What happens when I bring in my pet for a procedure involving anaesthesia?

When you bring in your pet it is generally given a drug which relaxes them and makes for a much smoother recovery from the anaesthetic. They are also often given a pain killer if the anaesthetic is part of a surgical procedure. Some pets may not have a pre-anaesthetic sedative because the veterinarian has decided that a different anaesthetic protocol is better for that individual.

When it is time for the anaesthetic the pets forearm is clipped to make it easier to see their vein and a anaesthetic drug is slowly injected. The dose is calculated, based on the size of the animal and whether a pre-anaesthetic was given. Usually just enough anaesthetic is given to allow us to then place a tube into the pets airway. This allows us to ensure there is a constant open airway and allow us to provide a steady mixture of oxygen and anaesthetic gas. There animal adsorbs the anaesthetic gas through their lungs and allows us to maintain a constant state of anaesthesia.

When the procedure is finished the anaesthetic gas is stopped and they are maintained on oxygen for a few minutes before being switched to normal air. The endotracheal tube that was placed in the windpipe is left in until the animal starts to swallow and is then removed. Once the pet is swallowing it is then placed back into its cage.

Most procedures usually allow the animal the pet to go home in the afternoon or evening

How do we monitor the anaesthesia?

The Karingal Veterinary Hospital employs a number of means to monitor the anaesthetics we give our patients to ensure it is as safe as possible. Here are some descriptions of equipment we use alongside the expert attention of our veterinary nurses

Apalert monitor. This registers each breath the animal makes and will sound an alarm if no breath is recorded after 30 seconds has lapsed

Pulse Oximeter. This registers the animals heart rate and degree of saturation of the patients blood with oxygen. (i.e. tells us that enough oxygen is getting in to the patient) Alarms sound if the patient drops below any preset parameters.

Blood Pressure Monitor Blood pressure and heart rate can be monitored during surgery with this. .

Is my pet to old for an anaesthetic?

This is generally a decision to be made by owner and veterinarian based on each individual case. However the anaesthetics available today for our use mean that any age animal can be safely anaesthetised. High risk patients have to have the risks of their conditions weighed up against any risks of anaesthesia. For instance dental disease presents a much higher risk to the geriatric patients than having an anaesthetic so the teeth can be cleaned.

If your veterinarian utilizes the latest drugs and equipment, you won't have to worry too much about the anaesthetic.

What about when my pet comes home?

After general anesthesia, animals are likely to be affected by the anesthetic drugs for several days. 

An animal may exhibit behavioral changes for several days after general anesthesia. They may act as if they do not recognize familiar surroundings, people or other animals. Behavioral changes after general anesthesia are extremely common; fortunately they usually resolve within a few days. Do not leave young children unattended with an animal that has just recovered from general anesthesia no matter how trustworthy that animal normally is. Remember, your pet has been through a lot and probably won't fully recover and be himself/herself for several days. There are reports of normally well-behaved dogs returning home after surgery and anesthesia and biting young children for no apparent reason. 

The pet’s ability to control its body temperature may be affected during the recovery period. Many anesthetics alter the temperature set point in the brain and cause blood vessels in the skin to dilate promoting heat loss. Conversely, an animal's natural cooling mechanisms may be unable to adequately respond to increases in environmental temperature. For the first few days after general anesthesia, it is recommended to keep your pet in a warm, though not overly hot room. Cold weather breeds such as Malamutes and Huskies tend to retain heat easily and a cooler environment may be more appropriate for these breeds. 

Obese animals often have delayed recoveries. Most general anesthetics are very fat soluble so the greater the amount of body fat and the longer the animal is anesthetized, the greater amount of anesthetic agent that will be absorbed into body fat. Anesthetic taken up by body fat will leach back into an animal’s blood for days or even weeks after anesthesia. This low residual amount of anesthetic may continue to affect an animal's behavior for several days.