Anaesthesia is the total loss of sensation in a body part or in the whole body, generally induced by a drug or drugs to create loss of feeling, unawareness and muscle relaxation either locally, regionally or centrally. There are many reasons for administering anaesthetics to animals; the main purpose is to provide a convenient, safe and effective means of facilitating medical and surgical procedures while minimising stress, pain, discomfort and adverse side effects to your pet and the veterinary team.
Many veterinarians are presented with the challenge of anaesthetising pets with pre-existing conditions in their practices. Conditions such as heart, lungs, liver and kidney disease, the age and weight of the animal all play a part in affecting anaesthetic management. Certain breed differences can also result in increased anaesthesia-related morbidity and mortality. Some examples are:
- Brachycephalic breeds (Pug, Boston Terrier, Pekingese, Boxer, Bulldog, Shih Tzu or any one of the other breeds with pushed in or short faces) – increased respiratory effort; potential for upper airway obstruction
- Herding breeds (e.g., Shetland sheepdog, Australian Shepherd, Border collie) – a genetic mutation that allows a select group of drugs to accumulate within the brain, which may cause marked sedation and respiratory depression.
- Toy breeds (eg, Shih Tzu, Pomeranian, Chihuahua, Papillion, Toy Poodle, Silky Terrier, Maltese) – lower body temperatures from large body surface area relative to body size; difficulty monitoring; low blood sugar
As with all aspects of medicine, complications will occur with anaesthesia. It has the potential to compromise your pet’s state of being at unpredictable times and in unpredictable ways, including causing animal death. Therefore, a thorough assessment of your pet is made before they undergo anaesthesia to maximise safety and minimise the potential for complications.
A pre-anaesthetic evaluation is essential before any anaesthesia to identify and address abnormalities. This includes finding out patient history and doing a physical examination. A pre-anaesthetic blood test may be performed to check blood sugar, liver/kidney values, and red blood cell count. Many pets will require more extensive pre-anaesthetic blood tests. Even in pets under one year old, blood work will occasionally detect abnormalities that could affect anaesthesia. These will often be performed on the same day of the procedure
A personalised anaesthesia plan will be created and addresses pre- and post-anaesthetic sedation and/or tranquillisation, induction and maintenance drugs, perioperative pain relief, ongoing physiologic support, monitoring parameters, and responses to adverse events.
You will be asked to withhold food and water for your pet before the day of procedure for a certain time to reduce the risk of regurgitation and aspiration, which means breathing in the contents of the stomach and gastric juices into the lungs. Your veterinarian or veterinary technician will explain the procedure to you and discuss the patient assessment and risks, the proposed anaesthesia plan, and any medical or surgical alternatives before obtaining informed consent to anaesthetise your pet and perform the procedure. To help reduce the risk of complications, it is very important that you follow the directions of the veterinarian, especially regarding patient preparation.
Every pet under general anaesthesia requires continuous monitoring of their vital parameters (heart activity, breathing, temperature and degree of consciousness). The goals of monitoring are to:
- Watch the physiological status of your pet
- Adapt anaesthesia depth to an adequate level
- Anticipate problems
A variety of monitoring equipment is available for determining your pet’s status during anaesthesia. Improved anaesthetic safety depends on both the correct use of equipment and the correct interpretation of information obtained. Written anaesthetic records are sometimes used. Despite the electronic aids available, the most important monitor still remains a dedicated vet / vet nurse who is constantly monitoring the patient.
Many drugs used for general anaesthesia tend to cause blood pressure to decrease. Intravenous fluids administered during anaesthesia will counter this decrease. In addition, if there are any adverse reactions under anaesthesia, an intravenous catheter allows immediate administration of emergency drugs.
All animals, especially cats and small dogs, lose a lot of body heat under anaesthesia. The resulting hypothermia can slow the anaesthetic recovery. Anaesthetised pets are placed on a recirculating warm water pad and / or under a warm air blanket.
Pets are generally intubated when undergoing anaesthesia, which means that they have an endotracheal tube placed through the mouth and into the trachea, through which anaesthetic gas is administered. The endotracheal tube allows controlled respirations if your pet is not breathing well on their own, and prevents regurgitation if the pet vomits under anesthesia.
Your pet is continuously monitored during the recovery period for after effects such as:
- Partial or complete airway obstruction
- Lack of oxygenation
- Low body temperature
- Nausea and vomiting
- Behavioural changes including delayed recovery of consciousness
Some effects may last for 12-24-hours after anaesthesia.
When your pet is awake, aware, warm, and comfortable, he or she will be discharged. But first, the veterinary team will:
- Review the procedure and how it went.
- Explain follow-up care, including when your pet can begin to eat and drink.
- Explain how to recognise signs of complications in your pet. It is important that you call your veterinarian immediately if your pet has a complication.
- Tell you when to bring your pet back for a re-check.
- In addition to telling you the instructions, the veterinary team should give you a written copy of the aftercare instructions.
Anaesthesia is more than the delivery of anaesthetic drugs. With proper perioperative assessment and appropriate patient monitoring, safe and successful anesthesia can be performed in any breed of dog.
References
1. “Veterinary Information Network (VIN) – For Veterinarians, By Veterinarians.” Veterinary Information Network (VIN) – For Veterinarians, By Veterinarians. Web. 18 Apr. 2015. <http://www.vin.com/>.
2. Muir, William W., John A. E. Hubbell, Richard M. Bednarski, and Phillip Lerche. Handbook of Veterinary Anesthesia. 5th ed. St. Louis: Mosby, 2013. Print.
3. Bednarski, Richard, et al. “AAHA Anesthesia Guidelines for Dogs and Cats.” American Animal Hospital Association. 1 Jan. 2011. Web. 16 Apr. 2015.
4. “Canine Anesthesia.” www.vetlearn.com. 1 Jan. 2011. Web. 17 Apr. 2015.
This article is written by Dr Clare Koh of The Joyous Vet Pte Ltd. Dr Clare Koh graduated from the University of Queensland. She has special interests in emergency and critical care and internal medicine. Dr Clare finds a great sense of satisfaction through helping pet owners and their fur kids. She believes that keeping up with the latest information in vet medicine will allow her to serve them better. Whenever away from the hustle and bustle of the clinic, Dr Clare winds down by watching movies, reading fiction, and cycling.
