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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]

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