Before the anesthetic procedure
There are many types of anesthetic regimes including the use of drugs that are injected into a vein or muscle or inhalant drugs that are breathed in and out of the body. Your veterinarian will select the anesthetic regime based on the health of your pet and on the type of surgical procedure to be performed.
An endotracheal tube and intravenous catheter are often placed prior to general anesthesia. Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â Ã‚Â After pre-anesthetic sedation, an intravenous (IV) catheter is placed into a vein in either a front or hind limb, or occasionally in the neck. An IV catheter is the patient’s lifeline while (s)he is under the effects of general anesthesia. Through the IV catheter your veterinarian will have ready access to your petÃ¢â‚¬â„¢s blood stream to administer fluids and other drugs during surgery. To prevent life threatening bacterial infections, it is important that the skin overlying the catheter site be clipped of fur and scrubbed with a surgical disinfectant.
General anesthesia is often begun by giving a short-acting anesthetic agent IV. As soon as the pet loses consciousness, a soft plastic tube (endotracheal tube or ET tube) is inserted into the windpipe and is connected to an anesthesia machine. The anesthesia machine is used to deliver an inhalant anesthetic in oxygen and other gases. Many anesthetic drugs can depress breathing; having an ET tube in place allows the veterinarian to assist or control breathing if it becomes necessary. The loss of consciousness that occurs during anesthesia is often accompanied by loss of the ability to cough and gag. In awake animals, coughing and gagging are protective reflexes which prevent inhaling stomach contents or other foreign materials into the lungs. Insertion of a proper size ET tube prevents inhalation of stomach contents into the airways and lungs during anesthesia.
At the completion of the surgical procedure, the concentration of the anesthetic that the animal is breathing is reduced and the animal slowly regains consciousness. When the pet regains its swallowing reflexes, the ET tube is removed and the patient is monitored until it is fully conscious.
Vital signs such as heart rate, respiratory rate, and blood pressure can be monitored using specialized devices.
Rapid-acting, anesthetic drugs are easier to control if they are continuously administered. The anesthetic is Ã¢â‚¬Å“titratedÃ¢â‚¬Â? to achieve the desired level of anesthesia and analgesia. In other words, most general anesthetics are “dosed to effect”.
The animal’s depth of anesthesia is determined by evaluating reflexes, muscle tone, and response of vital signs to surgical stimulation. If an animal is judged to be too light for the surgical procedure being performed, an increased amount of anesthetic is administered. Conversely, if the patient is judged to be in an excessively deep plane of anesthesia, the amount of anesthetic administered is decreased.
Newer anesthetics such as IsofluraneÃ‚Â® are less likely to aggravate a pre-existing abnormal heart rhythm. Additionally, inhalation agents such as IsofluraneÃ‚Â® enter and exit the brain rapidly, allowing for a rapid onset of and recovery from anesthesia.
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 petÃ¢â‚¬â„¢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 animalÃ¢â‚¬â„¢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.
A common question posed to veterinarians is about the “sensitivity” of a particular breed of dog or cat to anesthetic drugs. This is a difficult question to answer, as there are few scientific studies that have evaluated the sensitivities of different breeds of animals to anesthetics. Many of the reported breed sensitivities are based on the clinical experience of veterinarians. Many giant breed dogs seem to require less of a pre-anesthetic sedative (a smaller dose per unit of body weight) than miniature or toy breeds. The reason for this apparent difference is unclear.
It has been documented that sight hound breeds of dogs are more sensitive to some of the ultra short-acting thiobarbiturate induction drugs. The administration of thiobarbiturates for induction of anesthesia in sight hound breeds has been associated with a slower recovery from anesthesia. The reason for this breed sensitivity is unclear at this time but may be related to a difference in liver metabolism of the drug and/or differences in body fat. When sight hound breeds are to be anesthetized, it has been recommended that non-thiobarbiturate induction drugs be used to prevent a prolonged recovery from anesthesia.
Within the same breed, individual animals respond to the same anesthetic in differing degrees. Vigilant monitoring of vital signs during general anesthesia will enable the veterinarian to recognize and respond to life-threatening changes in heart and lung function.
A patient who displays an abnormal response to any drug (anesthetic or not) should be monitored carefully if the situation dictates that the same drug be re-administered at a later date.
Probably, the most desirable general anesthetic for a young, healthy dog is the one your veterinarian is most familiar with. There are a great many anesthetic drugs available to today’s practicing veterinarian, however most practitioners use a few carefully chosen anesthetics with which they have the most experience and the most confidence. Your veterinarian’s experience in the use of a certain anesthetic drug often will more than offset one or two undesirable properties of a general anesthetic agent.
1. Communicate concerns about your petÃ¢â‚¬â„¢s health to your veterinarian prior to scheduling surgery. Any signs of exercise intolerance, weight loss, a recent change in urination or defecation, and mental alertness are particularly informative and may require further diagnostic workup.