To experienced cat owners, nothing is quite as frightening as being told your cat needs to be anesthetized for a procedure. Anesthesia -- defined as a "loss of feeling or sensation" -- is commonly used in veterinary practices, and provides an essential tool for surgical or other painful procedures.
Certainly no one would ever expect their cat to be spayed or neutered without anesthesia. Therefore, a better understanding of some of the commonly-used types of anesthetics and analgesics (pain relievers), how they work, and their potential drawbacks, will help us make the best decisions when it comes to sedating our cats.
Cats are generally given sedatives or tranquilizers prior to the induction of anesthesia, or as a first step to induction. These drugs sedate and calm the animal for introduction of the mask or tracheal tube required for an inhalant anesthesia. They also allow for a smaller amount of general anesthetic, help to minimize vomiting, and foster a quicker recovery period. Sedating drugs are generally administered by injection, intravenously for the most part, although Ketamine can be given intramuscularly. Injectable anesthetics are often used for relatively quick procedures, such as C-sections or spay/neutering.
Injectable anesthetic agents fall into three main groups: Barbiturates, Dissociative Anesthetics (DAs), and Nonbarbiturate Hypnotics. Acepromazine, the most commonly used sedative, is used in conjunction with an analgesic, such as pethidine or buprenorphine to provide a reliable sedation.
Propofol (a nonbarbiturate hypnotic), is the "injectable of choice" for certain veterinary procedures, as it is quick-acting, offers a rapid recovery period, and rarely induces drug aftereffects. Dosage for propofol, as for all licensed drugs, is governed by the FDA. However, propofol is contraindicated for cats with certain liver diseases, since it is primarily metabolized via the liver.
Ketamine, (DA) has been widely used as both a pre-anesthetic drug, and in combination with other drugs, such as Acepromazine, as full anesthesia for some procedures. It is generally considered safe, although some people believe that certain breeds of cats or dogs may be at risk with its use. Ketamine is nonnarcotic and nonbarbiturate, but interestingly, is an hallucinogenic and is used by some people as a recreational drug for that purpose. Ketamine is contraindicated in cats suffering from renal disease (kidney) or hepatic lipidosis (a liver condition), and certain other conditions.
Isofluorane revolutionized veterinary anesthesia because of its safety (particularly with older or compromised patients), rapid recovery of the patient after surgery, and because it's not likely to induce nor exacerbate heart arrhythmias. Isofluorane lost its patent, so it's becoming less expensive than newer inhalants, and is still considered the anesthetic of choice in veterinary medicine for pregnant animals (including c-sections) and for animals with heart problems.
It has been said that there is no such thing as the perfect anesthetic, and there is always potential for risk with any of them. It therefore behooves us to do our homework prior to allowing any procedure requiring anesthesia, and to insist on a pre-anesthetic blood screening. This precaution is not a guarantee by any means (for instance, Cardiomyopathy will not show up on a blood panel), but it can help your veterinarian determine what is the best anesthetic or combination of anesthetics for your cat. Certain conditions may not obviate the need for anesthesia, but other precautions, such as heart monitoring and/or oxygen assistance can be added for additional safety.
Potential Hazards by Drug Name
This list is not intended to instill fear or to cause you to micromanage your veterinarian. Instead, use it as a guideline to ask questions. Your veterinarian will be glad to ease your mind about the type of anesthetic(s) he intends to use, and why.
- Barbiturates (thiopental, thiamylal, methohexital):
This drug has potential for respiratory depression with excessive doses. Prolonged anesthetic recovery can also be a problem when barbiturates are used in older animals, obese animals (who often require a higher dosage), or other animals with compromised hepatic and renal function, which decreases metabolism of the drugs.
- Ketamine: This anesthetic has the potential for depressed cardiac function, compromised respiratory function, including apnea (failure to breathe and/or sudden pulmonary edema or fluid in the lungs) for cats with cardiac disease or severe debilitation.
- Propofol (sold as PropoFlo, Rapinovet, and Dipravan): This drug can cause apnea when inducted quickly, and overdosage can cause cardiac arrest, however, ordinarily there are minimal effects on the cardiovascular system.
- Acepromazine: Because it is not an analgesic, acepromazine is usually used in conjunction with another sedative. It is contraindicated in animals with CNS (central nervous system) lesions, and can sometimes cause hypothermia.
- Halothane (inhalant): This drug can lead to cardiopulmonary depression, and a risk of malignant hypothermia in some breeds/strains.
- Isoflurane (inhalant): This drug could lead to respiratory depression and cardiovascular depression.
From University of Minnesota Guidelines for Anesthesia, Analgesia, and Sedation