Anaesthesia means, literally, loss of feeling, but is generally used
to mean that the patient is unconscious. Anaesthetics are the means by which
anaesthesia is reached; in other words they are substances that bring about
unconsciousness and loss of feeling. Animals have to be anaesthetised in order
to undergo any form of surgery and, usually, for such procedures as x-ray and
MRI scanning. This is called general anaesthesia, which means that it
involves the entire body. There is also local anaesthesia, which
involves only that part of the body to which it is applied, and is used for
such procedures as stitching a wound where it is not necessary to have the
animal completely unconscious.
Problems that occur with anaesthesia in wolfhounds are to do with general, not local, anaesthesia and where the word anaesthesia is used from now on it describes general, not local anaesthesia, unless a statement is made to the contrary.
General anaesthesia is also used in euthanasia, where an overdose of the anaesthetic drug is given in order to kill the animal. At one BSAVA Congress, Dr. Barbara Weaver, Reader in Anaesthetics at Bristol University Veterinary School, said that a general anaesthetic in animals or humans brings the patient to the point of death and it is only the skill of the anaesthetist and subsequent monitoring that ensures that the majority of patients recover. A survey carried out into anaesthetic deaths in animals at the Royal Veterinary College, Potters Bar showed that 1 in 700 comparatively fit dogs and cats died unexpectedly under a general anaesthetic. A comparable figure in humans would be 1 in 10,000
Wolfhounds, like all the Sighthound breeds, can have a problem with the barbiturate anaesthetics. This is because their ratio of bone to bodyweight is high. It is also true that large breeds require less anaesthetic per pound of bodyweight generally than smaller breeds because of the difference in their metabolic rate. When calculating the amount of anaesthetic to give, surface area should be used as the indication, not bodyweight. There are charts available for converting size and bodyweight to surface area in order to calculate the correct amount of anaesthetic required.
Wolfhounds are at risk anyway from the use of barbiturate anaesthetics because of being Sighthounds and a giant breed, but there are health problems they can have which will make them even more susceptible. These include heart disorders such as dilated cardiomyopathy (DCM) and arrhythmias such as ectopic beats, but von Willebrands disease (VWD, which see) and hypothyroid (which see) also predispose them to major problems with anaesthesia, including death. As anaesthetic drugs are processed by the liver, a hound with liver dysfunction could also have a problem and this is most likely to show up as the hound taking a very long time to recover from anaesthesia.
Strictly speaking, only completely healthy animals should be given general anaesthesia but this is obviously not going to be the case very often (except, possibly, for x-rays) since the reason for the ga in the first place is that the animal is either damaged or ill. However, defects of the heart, lungs and airways should be discovered before induction, which is the first part of anaesthesia. For victims of road accidents or major falls, x-rays should always be taken before induction because of the danger of there being damage to ribcage, lungs, pleura, etc.
If any problems are discovered in the initial examination, then an ECG may be taken, blood pressure checked, and checks made for electrolyte imbalance as this can affect both the heart and anaesthesia itself.
Wherever possible animals should be starved for 8-12 hours before anaesthesia. This is because of the danger of food in the stomach causing vomiting, which might be inhaled and block the airway.
It is usual to give a premedication to calm the dog, as a calm dog requires less anaesthetic. The premed usually includes drugs which will check the side effects of anaesthesia and will consist of sedative, pain killer, perhaps heart stimulant, anti-spasmodic, etc. It is given 20-30 minutes prior to anaesthesia. However, it should be borne in mind that wolfhounds can react badly to the barbiturate sedatives given in premedications. This is especially true of Acepromazine (ACP), of which more later.
Anaesthesia is carried out in stages, the first of which is Induction, which should be fast and smooth. There are two main ways of giving anaesthetics. One is to give gases, the other injection into a vein. Gas involves putting a mask over the nose, which would upset most dogs, and most of the gases have an unpleasant smell which a dog would object to. This method is normally only used in young puppies because the liver is not fully grown until six months of age and so a young puppy can not deal with other anaesthetic agents. Injection for dogs over six months is faster and more pleasant for both dog and anaesthetist.
Where there is a problem such as something wrong with the heart or lungs, an I.V. cannula (a plastic tube) is inserted into a vein before induction. This is because the veins collapse if the dog goes into a state of collapse and it would then be difficult if not impossible to insert a needle into a vein in order to give drugs in an emergency.
A plastic tube is inserted into the airway to keep it clear during the operation. When the dog is anaesthetised its muscles relax and the tongue can fall back and block the airway if there is no tube. If the dog has a tumour in the back of its throat, obviously a tube cannot be inserted and in such cases a hole has to be cut direct into the trachea from the outside in order to keep the airway open.
The second stage is maintenance of anaesthesia. The induction agent usually lasts only 3-4 minutes, so gas is generally used to keep the dog under. The most commonly used is halothane but there are others which have advantages in some cases, such as if the dog has a bad heart. Nitrous oxide (laughing gas) can be used as well as anaesthetic as it helps kill the pain and so less halothane is needed. Oxygen also has to be given. During anaesthesia the dog needs at least 30% oxygen and this is particularly necessary if the operation is going to last more than five minutes.
In some cases the dog has to be completely paralysed and so cannot breathe, in which case it has to be connected to a machine which forces air into the lungs. This is mostly for abdominal surgery and operations performed inside the chest cavity. The machines used are mostly modified versions of the ones used for human surgery.
It is possible to maintain anaesthesia by using the induction agent and this can be done simply by giving more when the animal starts to wake. A long lasting agent such as Immobilon can be given, which is then reversed after the operation.
Anaesthesia must be monitored closely. Firstly to check that the animal is actually unconscious, which can be done by checking the response to reflex stimuli such as brushing the eyelashes. Secondly to monitor respiratory rate, blood pressure, pulse rate, etc. Preparations have to be made to give fluids when necessary to replace lost blood.
Recovery from anaesthesia should also be fast and smooth, apart from some specific instances, such as with major fractures, when it is better slow. The speed of recovery is mainly reliant on the drugs used as some fade quicker than others. The recovery period is one of the most dangerous parts of surgery. Most drugs depress respiration and heart rate so that the dog requires more oxygen. If the dog gets too cold it will not recover from the anaesthetic because of the drain on the available oxygen. Shivering uses more oxygen, so a cold dog will take longer to recover. Also, the tongue can fall back and block the airway. It is an advantage if this period is short so that there is less time for things to go wrong.
A dog which has had surgery will almost certainly be in pain when it comes round, although it is difficult to tell how much pain is present. Pain killers work better if given before pain is felt, which is why a pain killer is usually given in the premed. The usual pain killers used after surgery are the morphine-type drugs, or local anaesthetic is infiltrated round the nerves which will be causing the pain.
As far as recovery from anaesthesia goes, most of us desperately want to have our hounds back in our care as soon as possible, but, if barbiturates have been used, this may not be the best thing for the reasons stated above. We cannot give extra oxygen, and it may be difficult to keep a hound warm enough without getting it too warm, which is just as risky. Obviously, decisions have to be made at the time, based on individual circumstances. However, if there is no-one at the veterinary office to monitor the hound, then it would be best to have it at home.
There are more recent additions to the anaesthetic arsenal, which are reversed by giving an antidote once the need for anaesthesia is past and wolfhounds (and other Sighthounds and large/giant breeds) do much better on these. In the UK it is Rapinovet, but this is not always given automatically as it is more expensive. However, it is worth asking (and paying) for. With this anaesthetic, your hound should be able to walk out to the car almost immediately whatever protocol it was anaesthetised for is completed, although it may well then become very sleepy and spaced out later. However, in older hounds this kind of anaesthetic may not be a good idea because of the likelihood of the hound reverting to a state of sedation once it has returned home.
Some dogs given this kind of anaesthetic can go into a comatose state for several days on reaching home. This is because the antidote reverses the pain killer part of the anaesthetic but not the sedative part. Also, with drugs such as Immobilon, the heart and lungs are affected thus reducing the amount of oxygen in the blood and, unless extra oxygen is given, there can be a shortage of oxygen to the brain and this can cause character changes such as apprehension or, occasionally, viciousness. Such changes are not, however, usually permanent.
When a hound has had a major problem during or following anaesthesia it is usually due to:
1. Overdosing. Even if the dosage rate has been worked out properly, based on surface area rather than bodyweight, it is not possible to calculate the exact amount of drug to give because there are so many variables for each animal. A calculated dosage should never just be given as a complete dose but should be trickled in slowly while checking the depth of anaesthesia which has been reached and stopping immediately the required depth has been attained. If the circulation is slowed by heart disease, the anaesthetic will take a long time to take effect and there is a risk of inadvertently giving an overdose.
2. Lack of constant monitoring of anaesthesia, which is often because there is no-one available to keep a check. For example, a solitary vet may move away to set up the x-ray or whatever and, if the dog then went into collapse, it would not be noticed immediately and remedial treatment might come too late. Also, monitoring during recovery needs to be maintained, which is not always possible in some practices.
3. An undiagnosed disorder such as von Willebrands disease, which makes an animal more susceptible to death from anaesthesia.
Anaesthesia and water deprivation before surgery may worsen some medical conditions, such as kidney disorders, and the dog may die some days or weeks after apparent recovery from surgery.
Barbiturate sedatives such as Acepromazine can have very serious effects on wolfhounds. Great care should be given with dosage and it is safest not to give these drugs at all, if they are not absolutely necessary. For conditions such as anxiety or behavioural problems, it is much better to use homeopathy and/or flower essences than to use barbiturate sedatives. Hounds have died or, at least, been completely unconscious for days, following what has been suggested as a normal dose for their size and weight.
Also, the sedative action may be prolonged in elderly dogs, and the heart action and breathing systems may be depressed in the same way as from an anaesthetic, but it is not easy to give respiratory support to a dog under sedation.
When I was taking Moppet for her first session of radiotherapy, it was suggested that she be given a sedative before we started off so that, by the time we reached the veterinary hospital, she would be ready for immediate anaesthesia. My vet suggested six tablets of ACP as the right dose for her. I gave her one and even so, by the time we arrived, she was completely off her legs and had to be carried on a stretcher to the hospital. I hate to think what might have happened had I given her the full suggested dose.
And when we had the problem with Gaia (mentioned in the Homeopathy section) when she was so restless and anxious every evening until the early hours of the morning, the vet gave her a dose of ACP which was supposed to calm her down and make her comfortable. It simply made her unable to walk off her anxiety because she could not stand up, let alone move about and that was far worse for her as it had no calming effect whatsoever.
I have always insisted on being present when my hounds have to be given anaesthetics, which was just as well in at least one instance. One bitch had to have an x-ray on her hips to find out why she was so lame and it was being done by a young vet new to the practice. He asked her weight, made some calculations, and filled up three syringes with anaesthetic. I watched, appalled, and then asked whether he was just going to pour all that lot into her, to which he said of course, it was the correct amount for a dog of her size. I insisted that he just trickle it in slowly and, since I made a fuss and was obviously willing to just walk out with her if I did not get my way, he did as I asked. She was completely out before she had two-thirds of the first syringe! He went white and was horrified at what might have happened had he done as he intended. I was just glad I had insisted on staying!
The following comes from the Clin Tech Small Anim Pract 1999 Feb;14(1):38-43 Anesthesia of the sighthound. Court MH Department of Pharmacology and Experimental Therapeutics, Sackler School of Graduate Biomedical Sciences, Tufts University, Boston, MA, USA.
" The sighthounds are an ancient group of dog breeds that have been selectively bred for high-speed pursuit of prey by sight. Probably as a consequence of this selection process, these dogs have a number of idiosyncrasies that can potentially adversely affect their anesthetic management. These include
(1) nervous demeanor which can lead to stress- induced clinical complications, such as hyperthermia;
(2) lean body conformation with high surface-area-to-volume ratio, which predisposes these dogs to hypothermia during anesthesia;
(3) hematological differences such as a higher packed cell volume and lower serum protein compared with other dog breeds which may complicate interpretation of preanesthetic blood work;
(4) Impaired biotransformation of drugs by the liver resulting in prolonged recovery from certain intravenous anesthetics, especially thiopental; and increased risks of drug interactions.
Safe anesthetic management of sighthounds should include sedative premedication and appropriate use of analgesic drugs to minimize perioperative stress. Thiopental, or any other thiobarbiturate, should not be used in these dogs. Propofol, ketamine/diazepam combination, and methohexital are recommended alternative intravenous anesthetics. Avoid coadministration of agents that inhibit drug biotransformation, such as chloramphenicol. Inhalation anesthesia using isoflurane is the preferred anesthetic maintenance technique. Core body temperature should be monitored closely and techniques to minimize hypothermia should be employed both during anesthesia and into the recovery period."
|Article by Dr. Becker on how some breeds have difficulty in handling anaesthesia|
|Article on Greyhound Anaesthesia by Susanne Stack, DVM|
The homeopathic remedy ARNICA can help enormously with any procedure such as surgery, x-rays, and so on. Give in a 30C potency twice a day for at least three days prior to the procedure, where possible, or every few minutes before if it is an emergency. This remedy will lessen bruising, help prevent haemorrhaging, and speed recovery. Following surgery give the same remedy in a higher potency such as 10M or 1M, one three times daily for 5-7 days. HYPERICUM is also useful as a pain killer, given in as high a potency as you can get. Homeopathic vets always use this.
With the Bach Flower Remedies, give CRAB APPLE prior to surgery, and a mixture of CLEMATIS, OLIVE, STAR OF BETHLEHEM and WALNUT afterwards, with RESCUE REMEDY given to any animal which is slow to recover from the anaesthetic.