General Anesthesia for Horses: Procedures, Uses & Risks – [Medication Guide]

Anesthesia refers to the loss of sensation and consciousness from administration of anesthetic medications. Anesthesia is a critical aspect of veterinary medicine, as it allows for life-saving or career-saving surgeries and diagnostic procedures that would otherwise be impossible to perform on horses.

Anesthesia for horses can be general or local. General anesthesia induces complete unconsciousness and affects the entire body, while local anesthesia numbs only a specific area, leaving the horse conscious.

The most common uses of general anesthesia in equine medicine include castrations, colic surgeries, and musculoskeletal surgeries. Although veterinarians make every effort to prevent complications, these procedures have a high risk of mortality, with around 1 – 2% of procedures ending in euthanasia or death.

Read on to learn more about general anesthesia in horses, including details about how a horse is “put under,” common medications used, complications, and preventative strategies veterinary teams use to avoid them.

Common General Anesthetic Medications for Horses

There are two main types of anesthetic medications used in horses: intravenous (into the bloodstream) and inhalational (breathed in by the horse). Many anesthetic protocols use a combination of both types, however some shorter procedures may only use intravenous anesthesia. ^[1]

Intravenous Anesthesia

Intravenous anesthetic agents are primarily used for induction (starting anesthesia) in horses. ^[1] Veterinarians can also use them to maintain anesthesia for short procedures. ^[1]

The most common intravenous anesthetic agent is ketamine, although some practitioners may use tiletamine or thiopental. ^[1] Ketamine is a dissociative anesthetic that prevents excitatory nerves, nerves that stimulate muscles and tissues, from firing. ^[2] Ketamine can also provide mild pain control for surgical procedures. ^[2]

Veterinarians combine ketamine with another anesthetic agent, as using the medication on its own can cause seizures. ^[1] Common medications combined with ketamine for intravenous anesthesia include: ^[1]

• Xylazine
• Detomidine
• Romifidine
• Diazepam or midazolam
• Guaifenesin

These medications provide muscle relaxation and sedation prior to administering ketamine, reducing the risk of seizures. ^[2]

Inhalational Anesthesia

Inhalational anesthesia is common in longer procedures, as it provides a steady dose of anesthetic agent to the horse, ensuring they do not wake up during the procedure. ^[1]

The veterinary team administers these medications through an endotracheal tube, a plastic tube inserted into the horse’s windpipe to provide oxygen and anesthetic agent. ^[1]

When horses breathe in inhalational anesthesia, the drug accumulates in the horse’s lungs and is rapidly absorbed through small blood vessels, producing an anesthetic effect. ^[1] The concentration of medication in the horse’s lungs determines the level of anesthesia achieved. ^[1]

After the procedure is complete, the veterinary team stops delivering inhalational anesthetic via the horse’s air supply. As the horse breathes, non-medicated air fills the horse’s lungs, reducing the anesthetic concentration. ^[1] Once the anesthetic concentration drops sufficiently, the horse wakes up. ^[1]

The most common inhalational anesthetic agent used today is isoflurane. ^[1] This medication stimulates anesthesia quickly, and has a short recovery period in most cases. ^[1] Other inhalational agents used in horses include: ^[1]

• Halothane
• Sevoflurane
• Desflurane

The exact mechanism of action for inhalational anesthetics is unknown. ^[2] They likely prevent the activity of nerves leaving the spinal cord and brain, resulting in immobility and unconsciousness. ^[2]

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Uses of General Anesthesia

Veterinarians tend to avoid using general anesthesia for horses unless absolutely necessary, as there are significant risks associated with anesthetic events.

Given this, general anesthesia is reserved for procedures where the horse must be completely unconscious. For other procedures, standing sedation is preferred as it has a lower risk of complications.

Common procedures conducted under general anesthesia include: ^[3]

• Castration
• Fracture repair
• Colic surgery
• Osteochondrosis dissecans (OCD) surgery
• Respiratory surgeries, such as to treat roaring
• Extensive wound and laceration repairs

Some veterinarians may use general anesthesia to treat unhandled horses, for the safety of the horse and the personnel involved.

Horses experiencing high stress or anxiety do not completely respond to the sedative medications used in standing sedation, potentially leading to sudden movement that may be dangerous for handlers. General anesthesia administered in a chute system or by dart gun may be necessary for these types of horses.

Anesthetic Procedure

General anesthesia is a high-risk procedure for horses, and often owners are not present for the procedure. By understanding exactly what happens during general anesthesia, owners may quell some of the anxieties they might have surrounding the anesthetic event.

General anesthesia in horses is performed in five steps:

• Preparation
• Induction
• Positioning
• Monitoring
• Recovery

1. Preparation

Before the procedure, the veterinarian assesses the horse’s overall health to determine if there are any abnormalities that may affect the anesthetic procedure. ^[2] These findings may change which medications the anesthetist uses, or the type of anesthetic procedure used. ^[2]

Unlike in human medicine and other veterinary species, equine veterinarians typically do not recommend fasting prior to anesthesia. ^[2] However, the grain component of the diet should be removed by 12 hours prior to anesthesia. ^[2]

In preparation for anesthesia, the veterinarian administers sedation and any other medications necessary prior to the event. These medications may include: ^[2]

• Anti-inflammatory medications
• Antibiotics
• Other medications specific to the procedure

They also place an intravenous catheter, which allows easy access to the bloodstream during the procedure. ^[2]

If the horse will be intubated (have a tube placed into their windpipe to deliver oxygen), the veterinarian also flushes the horse’s mouth to remove any food debris and prevent choke. ^[2]

2. Induction

Many equine hospitals have large, padded rooms for induction of anesthesia. The veterinary team positions the sedated horse next to a padded wall, then holds a padded panel against the horse’s other side. This allows the horse to collapse against a comfortable surface once the team gives the general anesthetic.

Some general anesthetic procedures occur on-farm, where padded rooms are not available. In these cases, the veterinarian selects a safe, open area with good footing for the anesthetic event. After administering the general anesthetic, they use the horse’s head to control their collapse and ensure they fall in a safe area.

For procedures over one hour in length, many veterinarians use an endotracheal tube to help supply oxygen to the horse. ^[2] Although horses can breathe on their own under anesthesia, the weight of their large abdominal organs can push against the lungs and make breathing inefficient. For longer procedures, this can result in hypoxia (low blood oxygen) that may damage internal organs.

After the horse collapses, the veterinary team places the tube into the horse’s windpipe through their mouth. The tube is hooked up to a ventilator, a specialized machine that provides oxygen and inflates the lungs. For horses receiving inhalation anesthesia, the ventilator also provides this medication with each breath. ^[2]

3. Positioning

The prolonged recumbency (laying down) associated with anesthesia is not normal for horses, as they spend most of their time standing. Lying down for long periods puts increased pressure on the horse’s muscles, skin, and bones due to their heavy body weight. ^[2]

This is an important consideration when the veterinary team is preparing for an anesthetic procedure. Prolonged pressure on the body can result in: ^[2]

• Muscle damage
• Skin sores
• Damage to nerves

Keeping this in mind, the veterinary team chooses a position that maximizes comfort for the horse, while also allowing them access to the procedure area. ^[2] Some procedures may require the horse to lay flat on their side, while others may require the horse to lay on their back. ^[2]

To help prevent tissue damage, many veterinarians use foam pads to position the horse. ^[2] These pads help distribute the pressure and allow the veterinary team to put the horse in the most anatomically comfortable pose possible. ^[2]

They also remove the horse’s halter, as the metal buckles can cause significant tissue damage when pressed against the horse’s face for a long period of time. ^[2]

4. Monitoring

Monitoring the horse’s health while under anesthesia is very important in preventing anesthetic complications.

The type of monitoring depends on the equipment the veterinary team has access to. Many equine veterinary hospitals have state-of-the-art monitoring equipment for their long anesthetic procedures. For veterinarians performing short, on-farm anesthetic procedures, they typically use a combination of portable equipment and their stethoscope.

Common components of anesthetic monitoring include: ^[1][2]

• Evaluating the level of anesthesia
• Blood pressure
• Heart rate and rhythm
• Respiratory rate
• Blood oxygen level
• Body temperature

5. Recovery

After the procedure is complete, the veterinary team recovers (wakes up) the horse from anesthesia. ^[2] Many of the complications associated with anesthesia occur during the recovery period. ^[2]

In hospital, the veterinary team moves the horse into a padded room with a non-slip floor. ^[2] They usually place the horse on a foam pad or air mattress to prevent tissue damage. ^[2] They also wrap the horse’s legs and place a padded halter on their head to prevent injuries when the horse attempts to stand. ^[2]

Most teams give a dose of sedation to help keep the horse calm as they wake up. ^[2] Additional sedation ensures that the horse does not try to stand up too early, when they are still feeling the effects of the anesthetic agent. ^[2] They may also cover the horse’s eyes, dim the lights, and ensure a quiet environment to prevent sudden stimuli from waking the horse up too soon. ^[2]

Depending on the veterinary team’s preference, they may allow the horse to recover unassisted (on their own) under supervision, or they may place ropes or slings to assist the horse in standing up. ^[2][4]

The recovery period can be very dangerous for personnel due to the unpredictable movements of the horse, so many veterinary teams choose unassisted recoveries. ^[2]

On farm, most anesthetic recoveries are unassisted. Typically, a member of the veterinary team will hold the horse’s head and neck down for as long as possible, to ensure that enough of the anesthetic has worn off before the horse attempts to stand. ^[2] Once the horse starts attempting to stand, the veterinary team stays at a safe distance to ensure personnel safety.

It can take up to 90 minutes for horses to recover from anesthesia, depending on the type of anesthetic used. ^[4]

After the horse stands successfully, they are closely monitored while the remaining anesthetic and sedation wear off. Once the horse can comfortably walk and appears alert, they can return to their stall or paddock for post-operative care.

Complications

Complications from general anesthesia are relatively common in horses compared to other species. The estimated anesthetic mortality rate for horses is around 1 – 2%. ^[5][6] For horses undergoing emergency surgery, the mortality rate is as high as 10%. ^[6]

Factors that increase the risk of horses developing anesthetic complications include: ^[6]

• Type of surgery, with orthopedic and colic surgeries having the highest mortality rates
• Age of the horse, with older horses having a higher risk
• Type of anesthetic procedure used
• Position of the horse during the procedure

Veterinary teams employ many preventative measures during the anesthetic process to reduce the risk of complications. Common measures include health monitoring, appropriate padding and positioning, and designing anesthetic protocols specific to the horse’s individual needs.

Common complications during anesthesia include: ^[5]

• Low or high blood pressure
• Low blood oxygen
• Low or high heart rate
• Abnormal heart rhythms
• Hemorrhage (bleeding out; externally or internally)
• Allergic responses to anesthetic agents

A potentially fatal complication during general inhalational anesthesia is malignant hyperthermia (MH). This condition triggers an exaggerated release of calcium in the skeletal muscles, resulting in massive muscle contractions. The horse stays in spasm and the abnormal muscle activity causes body temperature to rise to dangerous levels. ^[7] The gene for MH has been identified in Quarter horses, but not other breeds.

The veterinary team attempts to treat these complications as they arise. In some cases, the procedure may continue if the horse responds to the treatment provided. ^[2] If the problem continues, the team may abandon the procedure for the safety of the horse.

Most anesthetic complications associated with mortality occur during recovery, when horses can act unpredictably and may injure themselves. During the recovery period, common complications include: ^[5]

• Limb fractures
• Soft tissue injuries
• Nerve paralysis

Using a padded room and floor for recovery can help prevent these injuries. ^[2] Additional strategies include: ^[2]

• Wrapping the horse’s legs
• Bandaging over the horse’s shoes
• Providing a non-slip floor

Some veterinary teams use assisted recovery techniques such as ropes or slings to help stabilize the horse as they stand up for the first time, with the goal of preventing fall injuries. ^[2]

Horses may also develop upper airway obstruction or fluid in the lungs during the recovery period. ^[2] These conditions can rapidly cause death if not identified and treated promptly. ^[2] For this reason, anesthetic recoveries are monitored closely and emergency medications are kept close by the recovery suite. ^[2]

Summary

Anesthesia refers to producing a loss of feeling and consciousness by administering medication.

• General anesthesia allows for surgical interventions and other treatments that would be impossible to perform on a conscious horse
• The most common general anesthetic procedures are castrations, colic surgeries, and musculoskeletal surgeries
• General anesthesia has a high rate of mortality in horses compared to other species
• Veterinary teams use several preventative measures to reduce the risk of mortality during anesthetic events