Feline Anesthesia: Protocol, Side Effects and Complications

Feline anesthesia is a common procedure in many veterinary clinics, but research indicates that the risk of anesthetic mortality is greater in cats compared to dogs.

In 2018, the American Association of Feline Practitioners (AAFP) released updated safety guidelines aimed at reducing anesthetic-related fatalities. These guidelines focus on prevalent side effects and complications that can impact cats, covering everything from pre-operative assessments to post-anesthesia recovery.

The AAFP emphasizes the importance of a comprehensive pre-anesthetic evaluation for all cats. This includes gathering medical history and conducting a thorough physical examination. During the exam, it’s crucial to assess all body systems and document vital signs.

Additionally, it’s essential to monitor cats for signs of stress, as this is a significant risk factor for anesthetic complications due to catecholamine release. If a cat appears anxious, it’s advisable to reschedule the procedure and have the owner administer gabapentin before transporting the cat to the veterinary clinic.

Cats should also undergo fasting prior to anesthesia. While there is no definitive evidence for an ideal fasting duration, the AAFP recommends a fast of 3-4 hours before the procedure.

Incorporating the American Society of Anesthesiologists’ (ASA) physical status classification can also enhance the pre-anesthetic assessment. This system categorizes patients into five groups based on their anesthetic risk.

• ASA 1: Normal patient with no health issues.
• ASA 2: Patient with mild systemic disease (e.g., skin infection).
• ASA 3: Patient with severe systemic disease that is limiting but not incapacitating (e.g., well-regulated diabetes mellitus).
• ASA 4: Patient with uncontrolled severe systemic disease posing a life threat (e.g., gastrointestinal obstruction).
• ASA 5: Moribund patient not expected to survive 24 hours without surgery (e.g., severe shock and trauma).

Studies on feline anesthesia indicate that ASA status is a more reliable predictor of anesthetic complications than patient age, with cats having an ASA status of 3 or higher facing an increased risk. Additionally, senior cats (those over 10 years old) are at greater risk for surgical complications, irrespective of their ASA status.

Pre-anesthetic bloodwork is also advised to identify abnormalities that may not be apparent during a physical exam. A 2014 retrospective study found that nearly 10% of feline patients exhibit abnormalities in pre-anesthetic blood tests that could necessitate adjustments to their anesthetic plans.

The recommended pre-anesthetic testing may vary based on the cat’s life stage. The AAFP guidelines provide the following suggestions:

Once the pre-anesthetic evaluation is complete, pre-anesthetic medications can be administered.

Opioids such as buprenorphine, butorphanol, morphine, and hydromorphone are generally recommended for premedication in cats. Acepromazine may also be included, despite its inconsistent effects and potential to cause hypotension, due to its anesthetic-sparing properties.

Benzodiazepines should typically be avoided, as they can induce agitation or dysphoria. However, this response is less common in very sick or geriatric cats, where benzodiazepines may be appropriate.

Dexdomitor and other alpha-2 agonists can also be used for premedication. While these drugs are effective sedatives, they may cause side effects such as bradycardia, decreased cardiac output, vasoconstriction, and increased systemic vascular resistance.

Before inducing anesthesia, an IV catheter should be placed to facilitate the administration of induction agents, emergency medications if needed, and IV fluids during the procedure.

Additionally, the AAFP guidelines recommend creating a customized emergency drug sheet, including dosages for each patient. Suggested medications to have on hand include atropine, glycopyrrolate, epinephrine, lidocaine, atipamezole, and naloxone, along with fluid boluses for managing hypotension.

There are various veterinary anesthesia machines and induction drugs suitable for cats. Agents like Telazol® and ketamine/valium can be administered intravenously, intramuscularly, or subcutaneously, whereas propofol must be given intravenously.

Chamber induction should be avoided whenever possible, particularly in agitated cats that have not received premedication. These cats will require higher amounts of anesthetic gas to achieve sedation, leading to significant cardiovascular depression. The stress of chamber induction can trigger a large release of catecholamines, increasing the risk of arrhythmias.

Special care is necessary during intubation to minimize the risk of laryngospasm and tracheal tears. Airway-related complications, especially obstruction, are a common cause of anesthetic fatalities in cats during and after surgery.

Most adult cats can be intubated using a cuffed endotracheal tube sized between 3.5-5 mm. A small amount of 2% lidocaine (0.2 ml) can be used to facilitate intubation. The cuff of the endotracheal tube should be lubricated with a small amount of sterile, water-soluble lubricant. If laryngospasm occurs, provide oxygen and wait for it to resolve spontaneously.

Careful monitoring is crucial for anesthetized pets. The AAFP guidelines recommend tracking the following parameters:

• Physical Observation: Monitor heart rate, respiratory rate, pulse, mucous membrane color, jaw tone, palpebral reflexes, and response to surgical stimulation.
• Circulation: Evaluate through pulse, heart rate/rhythm, and blood pressure.
• Oxygenation: Assess using a pulse oximeter.
• Ventilation: Monitor with capnography (if available) or respiratory rate, which serves as a basic indicator but doesn’t provide information about tidal volume.
• Body Temperature: Keep track of body temperature throughout the procedure.

Each of these parameters should be assessed every 5 to 15 minutes throughout the duration of anesthesia.

Hypotension, hypothermia, and hyperthermia are three of the most frequently observed complications in cats after anesthesia.

Hypothermia

Hypothermia is a common complication during and after anesthesia. Anesthetized cats should have their body temperature closely monitored, and active warming measures should be employed as needed.

Limiting the amount of hair clipped from the cat, keeping the cat dry, and using warmed surgical scrub and IV fluids can also help prevent hypothermia.

Hyperthermia

Some cats may experience rebound hyperthermia after anesthesia, with temperatures rising as high as 41.1–42.2°C (106–108°F). This condition is often associated with certain opioids and ketamine.

Supportive treatment includes removing heat sources, using a fan, and administering naloxone. Notably, cats that experience significant hypothermia during anesthesia are at a greater risk for post-operative hyperthermia, highlighting the importance of preventing hypothermia.

Sixty percent of feline anesthesia-related deaths occur during the recovery period, typically within the first three hours after surgery. Patients should be closely monitored during this time, including heart rate, respiratory rate, pulse quality, pulse oximetry, blood pressure, and body temperature.

While it’s best for the patient to be in a quiet, calm environment, they should remain within the visual range of a veterinary team member. The intravenous catheter should not be removed until vital signs have normalized and the pet is in a sternal position.

Delayed recovery is often linked to hypothermia, so providing heat support is essential for any patient experiencing slow recovery. Intravenous fluids and oxygen therapy can also be beneficial in these cases.

Emergence delirium may occur in recovering cats, characterized by wild thrashing. In severe instances, a small dose of dexdomitor can be given to sedate the cat until the other anesthetic drugs have worn off. However, hypoxemia can produce similar behaviors, so it’s crucial to ensure the cat is oxygenating effectively; if not, oxygen therapy should be provided.

Cats face a greater risk of anesthetic complications compared to dogs, making it essential to implement specialized feline anesthetic protocols. Preventing stress before surgery and conducting a comprehensive pre-anesthetic evaluation can significantly reduce risks, along with employing suitable anesthetic techniques.

Close monitoring of patients during and after anesthesia is crucial for the early detection and management of potential complications.

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