While feline anesthesia is a routine procedure in many veterinary practices, studies show that the likelihood of anesthetic mortality is higher in cats than it is in dogs.
In 2018 the American Association of Feline Practitioners (AAFP) issued new safety guidelines in an effort to prevent anesthetic-related mortalities. These guidelines address some of the most common side effects and complications that tend to affect cats, from pre-operative evaluation to patient recovery.
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The AAFP recommends a thorough pre-anesthetic evaluation for all cats. This involves taking a medical history and performing a physical examination. During the physical exam, all body systems should be evaluated and all vital signs should be recorded.
Cats should also be observed for signs of stress, which has been observed to be a significant risk factor for anesthetic complications due to catecholamine release. Anxious cats should be rescheduled for a different day, with the owner giving gabapentin prior to loading the cat into its carrier for the trip to the veterinary clinic.
Cats should also be fasted prior to anesthesia. Although there is little definitive evidence to suggest an ideal fasting time in cats, the AAFP recommends a 3-4 hour fast prior to anesthesia.
The American Society of Anesthesiologists’ (ASA) physical status classification can also be a valuable component of pre-anesthetic evaluation. It divides patients into 5 groups, based upon anesthetic risk:
- ASA 1: normal patient with no health problems
- ASA 2: patient with mild systemic disease (for example, skin infection)
- ASA 3: patient with severe systemic disease that is limiting but not incapacitating (for example, well-regulated diabetes mellitus)
- ASA 4: patient with uncontrolled severe systemic disease that is a threat to life (for example, gastrointestinal obstruction)
- ASA 5: moribund patient, not expected to survive 24 hours without surgery (for example, severe shock and trauma)
Feline studies have shown that ASA status is a better predictor of anesthetic complications than patient age, with cats having an ASA status of 3 or higher experiencing a higher risk of complications. Senior cats (those over 10 years old) are also at a higher risk of surgical complications, regardless of ASA status.
Pre-anesthetic bloodwork is also recommended, to screen for abnormalities that cannot be detected upon exam. A 2014 retrospective study showed that nearly 10% of feline patients have abnormalities on pre-anesthetic blood work that warrant changes to the pet’s anesthetic plan.
Recommended pre-anesthetic testing varies, depending on the cat’s life stage. The AAFP guidelines suggest the following:
- Cats ≤ 2 years old: Retroviral testing required; complete blood cell count (CBC), serum biochemistry, and urinalysis (UA) recommended.
- Cats 3-6 years old: Retroviral testing, CBC, serum biochemistry, UA, T4, blood pressure, ECG, thoracic radiographs, and NT-proBNP recommended.
- Cats 7-9 years old: CBC, serum biochemistry, UA required; retroviral testing, T4, blood pressure, ECG, thoracic radiographs, and NT-proBNP recommended.
- Cats ≥ 10 years old: CBC, serum biochemistry, UA, T4, and thoracic radiographs required; retroviral testing, blood pressure, ECG, and NT-proBNP recommended.
Once the pre-anesthetic evaluation has been complicated, pre-anesthetic medications can be given.
Opioids such as buprenorphine, butorphanol, morphine and hydromorphone are generally recommended for premedication in cats. Acepromazine is also sometimes added, despite its inconsistent effects and tendency to cause hypotension, because it can have a beneficial anesthetic-sparing effect.
Benzodiazepines should be avoided since they may cause agitation or dysphoria. This effect is less common in very sick or geriatric cats, however, on which benzodiazepines may be therefore be used.
Dexdomitor and other alpha-2 agonists may also be used for premedication. These drugs are effective sedatives, but common side effects include bradycardia, decreased cardiac output, vasoconstriction, and increased systemic vascular resistance.
Prior to anesthesia induction, an IV catheter should be placed. This will allow delivery of induction drugs, emergency drugs (if necessary), and IV fluids while the pet is under anesthesia.
Additionally, the AAFP guidelines recommend that a customized emergency drug sheet (with dosages) be calculated for each patient. Recommended dosages to have available include doses and volumes of atropine, glycopyrrolate, epinephrine, lidocaine, atipamezole and naloxone, as well as fluid boluses to administer in the case of hypotension.
There are a variety of veterinary anesthesia machines and induction drugs that can be appropriate for cats. Drugs such as Telazol® and ketamine/valium can be administered either intravenously, intramuscularly, or subcutaneously, while propofol must be administered intravenously.
Chamber induction should be avoided if at all possible. This is especially true in agitated cats that have not received premedication. Agitated cats will require high amounts of anesthetic gas in order to go to sleep, resulting in significant cardiovascular depression; the large release of catecholamines triggered by the stress of chamber induction may also result in an increased likelihood of arrhythmias.
Special care must be taken during intubation in order to reduce the likelihood of laryngospasm and tracheal tears. Airway-related problems, especially obstruction, are a common cause of anesthetic death in cats during and after surgery.
Most adult cats can be intubated with a 3.5-5 mm cuffed endotracheal tube. A small amount of 2% lidocaine (0.2 ml) can be used to to facilitate intubation. The endotracheal tube cuff should be lubricated with a small amount of sterile, water-soluble lubricant. If laryngospasm occurs, administer oxygen and wait for the laryngospasm to spontaneously resolve.
Feline anesthesia monitoring
Careful monitoring is essential for anesthetized pets. The AAFP guidelines recommend monitoring of the following parameters:
- Physical observation: heart rate, respiratory rate, pulse, mucous membrane color, jaw tone, palpebral reflexes, response to surgical stimulation
- Circulation: evaluated via pulse, heart rate/rhythm, blood pressure
- Oxygenation: evaluated via pulse oximeter
- Ventilation: evaluated via capnography (if available) or respiratory rate (a crude indicator of ventilation, because it does not provide info about tidal volume)
- Body temperature
Each of these parameters should be assessed every 5-15 minutes for the duration of anesthesia.
Anesthesia complications in cats
Hypotension, hypothermia and hyperthermia are three of the most commonly observed complications in cats following anesthesia.
Hypothermia is a common complication during and after anesthesia. Anesthetized cats should have their body temperature closely monitored, with active warming utilized as needed.
Limiting how much of the cat’s hair is clipped, keeping the cat dry, and using warmed surgical scrub and IV fluids can also help prevent hypothermia.
Some cats experience a phenomenon known as rebound hyperthermia after anesthesia, in which their temperature may rise as high as 41.1–42.2°C (106–108°F). Hyperthermia is associated with a number of opioids, as well as ketamine.
Treatment is supportive in nature, including removing heat sources, using a fan, and administering naloxone. It has been shown that cats experiencing significant hypothermia under anesthesia are at higher risk of post-op hyperthermia; this underscores the importance of preventing hypothermia.
Sixty percent of feline anesthesia deaths occur in the recovery period, typically in the first three hours after surgery. Patients should receive careful monitoring during this time, including heart rate, respiratory rate, pulse quality, pulse oximetry, blood pressure, and body temperature.
Although it is best for the patient to be in a quiet, calm area, the patient should remain within visual observation of a veterinary team member. The intravenous catheter should not be removed until vital signs have returned to normal and the pet is sternal.
Delayed recovery is often attributable to hypothermia, so heat support should be considered in any patient experiencing a slow anesthetic recovery. Intravenous fluids and oxygen therapy can also be beneficial in such cases.
Emergence delirium may also occur in recovering cats, characterized by wild thrashing. In severe cases, a small amount of dexdomitor may be administered, sedating the cat until the other anesthetic drugs have had the opportunity to wear off. Hypoxemia may cause similar behaviors, however, so it is important to make sure the cat is oxygenating effectively; if not, provide oxygen therapy.
Cats are at a higher risk of anesthetic complications than dogs, so special care should be given to feline anesthetic protocols. Preventing stress prior to surgery and conducting a thorough pre-anesthetic evaluation can help minimize risks, along with using appropriate anesthetic protocols.
Patients should be closely monitored, both during and after anesthesia, in order to allow early detection and correction of complications.
Sources and additional reading
- Dyson DH, Maxie MG, Schnurr D. 1998. Morbidity and mortality associated with anesthetic management in small animal veterinary practice in Ontario. J Am Anim Hosp Assoc. 34: 325–335.
- Robertson S, et al. 2018. AAFP Feline Anesthesia Guidelines. Retrieved from https://journals.sagepub.com/doi/full/10.1177/1098612X18781391
- Davies M, Kawaguchi S. 2014. Pregeneral anaesthetic blood screening of dogs and cats attending a UK practice. Vet Rec. 174: 506.
- Posner L, et al. 2007. Post-anesthetic hyperthermia in cats. Veterinary Anaesthesia and Analgesia. 34: 40-47. Retrieved from https://www.vaajournal.org/article/S1467-2987(16)30904-7/pdf
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