How Long Does Anesthesia for Cats Last?

Many people confuse sedation with anesthesia. Although related, they refer to the different stages of sensation loss. These are:

• Local anesthesia: sensation is lost only in a localized part of the body, but the animal otherwise remains consciousness.
• Sedation: this is when the cat's central nervous system is depressed, preventing the animal from feeling pain, but not losing consciousness.
• General anesthesia: suppress the central nervous system to the point the cat does not feel any sensation and is completely unconscious.

The type of anesthesia you cat will receive depends on the type of surgery. If the surgery is invasive, it is likely they will need general anesthetic. However, this will be determined by the veterinarian when they carry out a pre-anesthetic exam. This is an assessment to understand the clinical picture of the cat and their overall health. They will check:

• Complete medical history (existing diseases and medication)
• Physical examination (vital signs, mucous membranes, capillary filling time and body condition)
• Blood analysis and biochemistry
• Urine analysis
• Electrocardiogram to assess the state of the heart
• In some cases x-rays or ultrasound

The recovery time for a cat coming out of surgery depends on many factors. First, there is a difference between regaining consciousness and recovery. Once the anesthetic wears off, it doesn't mean the cat is fine again. Some procedures require rest while the cat can recuperate and their body heals, what we refer to as recovery.

How long it takes for a cat to regain consciousness after being given anesthetic will depend on the drugs which have been administered. Different combinations of sedatives, tranquilizers and painkillers (analgesics) can be used, including:

Phenothiazines (acepromazine)

Acepromazine is a sedative derived from phenothiazine. In humans it has been administered as a type of antipsychotic drug, but it is used for sedation in animals. It takes a maximum of 20 minutes to act and sedation lasts about 4 hours. The animal must be oxygenated if it is used as a sedative due to the cardiovascular depression it produces. It is characterized by:

• Antiemetic (does not induce vomiting)
• Deep sedation
• It has no antagonist, so the cat will wake up when the drug has metabolized
• Bradycardia (low heart rate)
• Hypotension (low blood pressure) lasting up to 6 hours
• They do not produce analgesic effects
• Moderate muscle relaxation

Veterinarians have to be careful administering this drug as different cats may react differently to the same dosage. It can also cause spontaneous motor activity or lead them to be startled easily.

Alpha-2 adrenergic agonists (xylazine, medetomidine and dexmedetomidine)

They are sedatives that take a maximum of 15 minutes to act and have a shorter sedation duration, only about 2 hours. They have an antagonist (atipamezole), so if it is used they will wake up after a short time without having to wait the necessary time until the sedative effect disappears. It must be oxygenated due to the cardiovascular effects. They produce:

• Good muscle relaxation
• Moderate analgesia
• Emetic (induces vomiting)
• Bradycardia
• Hypotension
• Hypothermia (low body temperature)
• Diuresis (more urine production)

Benzodiazepines (diazepam and midazolam)

These cause a relaxing effect which take up to 15 minutes to act, but last from 30 minutes to 2 hours. They have an antagonist (flumacenyl) and produce the following effects:

• Powerful muscle relaxation
• No effect on the cardiovascular system
• Not sedative
• They do not produce analgesia

Opioids (butorphanol, morphine, methadone, fentanyl and pethidine)

These are strong pain relievers often used together with sedatives to aid sedation or to prepare the cat for anesthesia. They tend to depress the cardiorespiratory center and some, like morphine, are emetic (causes vomiting in cats). In the past it was believed that opioids such as morphine were contraindicated in cats due to the stimulant effects they produced.

At present opioids are not contraindicated and they can be used without problems. However, due to their strength, maintaining the right dosage, type of administration, schedule and combination of drugs is vital. Exceeding the correct dose can cause various problems such as dysphoria, delirium, motor excitability and seizures.

While butorphanol produces less analgesia and is used in sedation or for premedication before general anesthesia, methadone and fentanyl are the most used in this species to control pain during surgery. This is due to their greater analgesic potency. They have an antagonist to reverse their effects called naloxone (often sold under the brand name Narcan).

The duration of sedation will depend on the metabolism and the condition of the cat itself. The average is about 2 hours if sedation is not reversed with the antagonist. By combining two or more drugs of a different class, it allows enhancement of the desired pharmacological effects and thus reduce doses and side effects. For example, the combination of butorphanol with midazolam and dexmedetomidine is usually very effective to sedate a nervous, sore, stressed or aggressive cat in consultation. Having an antagonist reverses the effects, being able to return home awake or only slightly drowsy.

For us to know more about the recovery time for cats which have had anesthetic, we need to look at how anesthetics act on felines. Anesthetic procedures in veterinary medicine consist of four stages:

Stage 1: premedication

The main objective of administering medication prior to the anesthetic is to create and ‘anesthetic cushion’. This is in aid of reducing potential for side effects as well as reducing stress, fear and pain the cat may experience. Different combinations of the sedatives, muscle relaxants and analgesics mentioned above are used.

Stage 2: induction of anesthesia

The administration of an injectable anesthetic such as alfaxalone, ketamine or propofol is used make the cat lose reflexes. This can allow intubation (introduction of a tube into the feline trachea for the introduction of the inhalation anesthetic) to continue the anesthetia process.

These phases usually last about 20-30 minutes in total until the drugs take effect and allow the next step.

Stage 3: maintenance

It consists of the continuous administration of an anesthetic agent. They will be administered in one of the following forms:

• Inhalation: (such as isoflurane) along with analgesia (opioids such as fentanyl, methadone or morphine) and/or non-steroidal anti-inflammatory drugs, such as meloxicam. This will reduce pain and inflammation in the postoperative period. The latter can also be administered at the end of anesthesia together with an antibiotic to prevent possible infections.
• Intravenous: propofol and alfaxalone in continuous infusion or repeated injections together with a strong opioid such as fentanyl or methadone. Its use for more than one or two hours. It is not recommended in cats which need to avoid slow recoveries, especially with propofol.
• Intramuscular: ketamine and opioid for short 30 minute surgeries. If a little more time is required, a second dose of intramuscular ketamine can be given, but not more than 50% of the initial dose.

The duration of this phase is variable and will depend on the type of surgery that your cat is going to undergo. If the cat is being castrated they will need less anesthesia, about the same as obtaining biopsies. If a foreign body is being removed from the gastrointestinal system, it can take a little longer. Severe trauma operations can last several hours. Amounts will also depend on the skill of the veterinary surgeon and possible intraoperative complications.

Stage 4: recovery

After the anesthesia's effects start to wear off, the resuscitation begins. This should be quick, gentle, stress-free and painless if the correct drugs have been used and precautions have been taken. It will be necessary to monitor the cat's condition and their temperature, as well as observe for possible complications. These can manifest in fever, vomiting and more. In general. a well-fed healthy cat usually has a full anesthesia recovery time of 2 days.

The duration of anesthesia varies according to:

• Duration of surgery
• State and metabolism of the animal
• Skills of the surgeon
• Presence of complications
• Drugs used
• Resuscitation time

While some anesthesics last an hour or less, others can last for several hours. With a correct anesthetic protocol, analgesia, control of vital signs and temperature by the anesthetist, your cat will be safe and without feeling any pain or stress regardless of the duration of anesthesia.

The time an animal can take to recover from anesthesia will depend on the type of anesthetic and amount that has been administered. Complications may arise related to the surgery, so we need to be very careful. However, there are normal reactions cats experience with anesthetic. For example, even if a cat fasts before surgery, it is possible they will vomit some bile or food remnants. This is relatively normal if alpha-2 sedatives or opioids have been used.

It is also normal that, after waking up, the is disoriented or meows for no reason. It may take a few hours for the cat to want to eat and they may urinate a lot to eliminate the excess liquid administered with fluids during anesthesia. During recovery, cats need to be in a warm, dark, and quiet place with as little stress as possible.

Sometimes cats can take a long time to wake up from anesthetic. Keep in mind that cats are very different from dogs in many ways. In particular, the metabolism of drugs in cats is much slower than in dogs, so they can take longer to wake up. Your cat may take longer to recover from anesthesia for the following reasons:

Enzyme deficiencies

One of the most important pathways of drug metabolism is glucronic acid conjugation. However cats have a deficiency of the enzyme glucuronyltransferase which is responsible for this process. For this reason, the metabolization of drugs that use this route is much slower when having to use an alternative: sulfoconjugation.

The origin of this deficit is found in feline diet. Being strict carnivores they have not evolved to develop systems to metabolize phytoalexin from plants. Therefore, in cats certain drugs (ibuprofen, aspirin, paracetamol and morphine) should be avoided or used at much lower doses than in dogs that do not have this problem.

Propofol as an anesthetic

The use of propofol in maintenance as an anesthetic for more than one hour can lengthen recovery times in cats. In addition, repeated propofol anesthesia in felines can cause oxidative injury and the production of Heinz bodies (inclusions that form on the periphery of red blood cells by destruction of hemoglobin).

Drug overdose

Cats tend to weigh relatively little, especially if they are small. They can be given too large a dose more easily. The result is a prolonged recovery time. In these cases, only antagonist drugs would be indicated, but taking into account that awakenings can be sudden and dysphoric. In fact, the tendency is to try more progressive and slower wakings, using relaxants such as benzodiazepines to do so if necessary.

Hypothermia

Hypothermia in cats results in a drop in body temperature, something common due to their small size and weight. The more their temperature falls, the more difficult is the drug metabolization due to the reduction in enzyme function, lengthening recovery and awakening from anesthesia. This condition should be prevented by applying insulating materials to the animal and covering them with blankets or using heated surgical tables, applying tempered fluids, as well as maintaining the operating room temperature at around 21-24 ºC (69.8 - 75 ºF).

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