Anesthesia and It’s Effects in Cats

By:  Dawn Skupin

Cats usually require surgery at some point in one of their “nine” lives.  Quite often this can be done as routine neuter or spay procedure.  With advances in veterinary anesthesia today, the anesthesias administered are quite safe.  It is important to realize that anesthesia is not a routine drug.  Anesthesia has a profound effect on the cat’s physiology because of the generalized central nervous system effect as well as specific effects on all other body systems. 

Anesthesia is a state of unconsciousness induced in the animal.  There are three components of anesthesia.  They are analgesia (pain relief), amnesia (memory loss), and immobilization.  The medications used to induce anesthesia have varying effects in each of these areas.  Some drugs may be used individually to achieve all three.  Others have only analgesic or sedative properties and may be used individually for these purposes or in combination with other drugs to achieve full anesthesia.

Anesthetics are drugs used to block the sensation of pain. Pain is difficult to assess in cats because of the inability to communicate directly about what the animal is experiencing.  Therefore, it is assumed that if something is painful to a human it will also be painful to an animal. Animal welfare regulations require that analgesia be provided whenever a procedure is being performed or a condition is present that is likely to cause pain to the animal.

There are two categories of anesthesia:  local anesthesia and general anesthesia.  Localized anesthesia is injected into the tissues and regional nerves around the area of the procedure.  It may be applied to mucous membranes.  Local anesthetics, such as xylocaine, lidocaine, mepivacaine and bupivacaine have the fewest risks and side effects but are not suitable for most surgeries. Local anesthesia is primarily used for wound closure and removal of small tumors, whereas sedation without general anesthesia is used for more involved or prolonged procedures.  Sedatives used for more involved procedures may include acepromazine, diazepakm, xylazine and medetomidine. The guidelines regarding the dosage of injectable anesthetic is computed by the cat’s weight.   

General anesthesia is used for major surgery.  It relaxes the cat’s entire body, blocks all pain sensation and renders the cat unconscious.  It may be administered by injection or inhalation. With gas anesthesia, the mixture of oxygen and anesthetic is balanced.  The dose is adjusted according to the breathing of the cat.  The exact dosage is customized to the individual animal. Inhaled gases such as Halothane, Isoflurane and Sevoflurane are administered through a tube placed in the trachea or the cat can be masked.  The advantage of gas anesthesia is the control of the depth of the anesthesia; it can be deepened or lightened as needed during a procedure.  If a complication arises during surgery the cat can be awakened almost immediately if it is safe to do so.  

While there is no 100% safe anesthesia, gas anesthesia has the fewest risks associated with it. With gas anesthesia, the cat wakes up shortly after the gas is discontinued.  If injectable anesthesia is used, the cat can take 24 or more hours before the animal returns to normal.  Inhalation anesthesia is superior to most injectable forms of anesthesia in safety and efficacy.  Because the anesthetics are eliminated from the blood by exhalation, with less reliance on drug metabolism to remove the drug from the body, there is less chance for drug-induced toxicity.  Inhalations anesthetics are safer for use in sick or debilitated animals because there is minimal metabolism.

Combinations of anesthesia are often used to lessen potential side effects.  Ketamine and xylaziine are commonly used injectable anesthetics used together for short surgeries.  Injectable drugs often keep the animal under the influence of the anesthetics for a longer period of time, thereby lessening the onset of pain to the animal.

Certain breeds of cats have an increased sensitivity to barbiturates and other anesthesia.  This may be related to the structure of the animal.  Factors may include short faced cats, such as Persians, or confirmation, like Siamese, contribute to the weight or fat and the amount of anesthesia required for proper administration.

Occasionally anesthesia can cause upset stomach resulting in vomiting both before and after surgery.  Vomit can cause a blocked trachea and cause asphyxiation.  To avoid this, keep the stomach empty for 12 hours prior to surgery.   Food and water should be removed the night before the scheduled surgery.    Diabetic cats may need adjustments in their feeding schedule and insulin injections.  Small, frequent meals should be fed to the cat for the first 24 hours post-surgery.

Cats, especially kittens, are unable to regulate their body temperature while under anesthesia.  The longer a cat is under anesthetic the more the body temperature drops.  It is important that the cat or kitten be kept warm during the surgery and recovery.

Anesthesia is eliminated from the cat’s system by the lungs, liver and kidneys. Impaired function of the organs can cause dose-related complications.  A reaction to the anesthetic is one of the most dangerous side effects of anesthesia.  Respiratory distress, such as labored or stopped breathing, heart arrhythmia and failure are examples of the side effects of general anesthetic.  If the cat has a history of lung, liver or kidney disease, the risk from anesthesia is elevated.  These animals require adjusted anesthetic to attain the needed depth of anesthesia or may take longer to become fully aware after their anesthesia.  Pre-surgery blood work is suggested to detect any possible problems.  Geriatric animals should always have a complete blood work profile before anesthetic.  Often, the side effects exacerbate an underlying problem in the cat such as cardiac or lung disease.

In rare cases anesthesia can cause temporary behavior changes in the cat.  The cat may not recognize the owner or other pets in the household.  They may act shy or timid, whereas before surgery they were friendly and outgoing.  Most behavior changes should return to normal within a few days.  If the condition persists, a veterinarian should be consulted.

Some of the more commonly used anesthesia for cats include:

Injectable Anesthetics:

Ketamine is controversial drug that has been widely used as a pre-anesthetic drug and in combination with other drugs as full anesthesia for some procedures.  It is generally safe however some believe that certain breeds of cats, (and dogs), may be at risk with its use.  Ketamine is a rapid-acting drug and has a hallucinogenic effect although it is a nonnarcotic and nonbarbiturate drug. It is administered as an intramuscular injection. Following administration of the recommended dose, cats become ataxic in about five minutes with the anesthesia usually lasting from 30 to 45 minutes.  At lower doses, complete recovery usually occurs in four to five hours but with higher doses recovery time may take as long as 24 hours.   

Ketamine is contraindicated in cats afflicted with kidney or liver disease.  Ketamine has a potential for depressed cardiac function; compromised respiratory function, including apnea, (failure to breathe and/or sudden pulmonary edema.  Pulmonary edema is fluid in the lungs.) It also should not be used in cats with severe debilitation. Ketamine is contraindicated for cats diagnosed with head trauma.  In addition, although it is a rare side effect, Ketamine can potentially change a cat’s personality.  This can be a temporary condition, but it can also be a permanent condition.  In cats, cases of prolonged recovery and death have been reported.

Propofol (a nonbarbiturate hypnotic) is the injectable of choice for specific veterinary procedures.  It is fast acting, with a rapid recovery time, and it seldom induces drug aftereffects.  Overdose can cause cardiac arrest, however ordinarily there are minimal effects on the cardiovascular system.  The FDA governs the dosage, as they do with all licensed drugs.  Propofol is contraindicated in cats with certain liver diseases since it is primarily metabolized in through the liver.

Barbiturates (pentobarbital, thiopental, thiamylal, methohexohexital)  these drugs have a potential for respiratory depression with excessive doses.  They are contraindicated in pregnant cats.  A prolonged anesthetic recovery can be a problem when barbiturates are used in older animals or obese animals, which require a higher dosage.  Cats with compromised hepatic and renal function decreases metabolism of the drugs.  Pentobarbital is no longer accepted for anesthetic induction due to its prolonged rough recovery.

Acepromazine  It is not an analgesic, consequently, 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.

Inhalant Anesthetics:

Isofluorane, particularly with older or compromised cats, this gas anesthesia revolutionized veterinary anesthesia.  Isoflurorane gas does not induce or exacerbate heart arrhythmias.   It is  considered the anesthesia of choice in veterinary medicine for pregnant animals and for animals with heart problems. Additionally, Isoflourane gas has recently lost its patent so it is becoming less expensive than the newer inhalants.

Sevoflurane is a relatively new anesthesia to the market, costing about four times more than Isofluorane.  Sevoflurane is a very fast acting gas anesthesia which results in a quick loss of consciousness and a quick return to consciousness.  Because of its cost, Sevoflurane is often used to induce anesthesia and then a switch to Isoflurane to maintain anesthesia during a procedure.  Both Isofluorane and Sevoflurane gases are very commonly used in human medicine.

Halothane gas costs even less to use than Isofluorane.  However, halothane produces a dose related depression of both the respiratory and cardiovascular systems.  Cardiopulmonary depression may be insignificant during short routine procedures performed on healthy cats, but may have significant effects in animals that have compromised cardiopulmonary function, especially if cardiopulmonary support is not instituted.

While anesthesia is necessary to prevent pain or distress, it must not be ventured into lightly.  The animals overall health in addition to the surgery necessary and the anesthesia used to do it must be considered as the whole picture.

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