Equine Sedation and Anaesthesia

General Points and Anesthetic Risk

Risk Management

  • Equine anesthesia emphasizes risk management over complex drug protocols

  • Requires close teamwork among anesthesiologists, surgeons, and nurses

  • High-risk procedures for horses and staff due to the size and weight of horses

Key Responsibilities

  • Practitioners may need to sedate, induce, or euthanize horses in emergencies

  • Monitoring during equine anesthesia is a foundational skill in equine practice

Legal Aspects of Equine Anesthesia

Horse as a Food-Producing Animal

  • Legally categorized as a food-producing animal, impacting drug legislation (unless declared otherwise).

  • Three drug options under cascade:

    1. Use licensed products for horses

    2. Use drugs on the essential substance list for horses

    3. Use drugs from the GBMRL register with established Maximum Residue Limits (MRL)

Drug Legislation Variations

  • Cascades: Vary by country (e.g., Northern Ireland vs. EU)

  • Essential List: Identifies drugs essential for horse treatment, all on the list have a withdrawal period of six months and apply to various equid species

    • Examples of anesthetic drugs from the essential list to be discussed later

Non-Food Producing Status

  • Horses may be declared non-food producing via a signed veterinary passport (Section 9)

  • Important for practitioners to recognize competition regulations, as drugs might affect competition eligibility

Anesthetic Risks in Horses

Mortality Risk

  • Mortality risk in ASA I and II horses undergoing general anesthesia is 0.6% (less than 1 in 100) significantly higher than in humans.

  • Factors contributing to higher risk include:

    • Horse temperament leads to panic and potential self-inflicted injuries

    • Heavy body weight causes tissue ischemia and ventilatory compromise

    • Obligate nasal breathers are prone to airway obstruction

    • Vulnerability to colic due to displaceable GI tract and risk of fractures

Phases of Anesthesia

  1. Induction Phase: Risk of excitement, complications with IV drug administration, trampling, and adverse drug reactions

  2. Maintenance Phase: General risks associated with anesthesia, particularly positional trauma and complications

  3. Recovery Phase: Highest risk, most complications occur here, such as myopathies and fractures

Anesthetic Risk Mitigation Strategies

  1. Whenever possible, avoid general anesthesia; prefer standing sedation for surgeries

  2. Actively monitor and address any abnormalities during anesthesia

  3. Aim to minimize anesthesia duration; risks increase significantly beyond 2-3 hours

  4. Collaboration among veterinary staff improves efficiency and safety

Sedation and General Anesthesia

Sedation Basics

  • Common sedative protocol:

    • Use alpha-2 agonists (e.g., xylazine, detomidine, romifidine) and possibly an opioid (e.g., butorphanol)

    • Induction typically with ketamine and midazolam or diazepam

  • Notable sedatives and their impacts:

    • Alpha-2 Sedatives: Provide effective sedation, monitor for ataxia and bradycardia, potential respiratory depressant effects

    • ACP: Limited sedative effects, risk of vasodilation and hypotension, contraindicated in extreme stress or hypovolemia, especially in stallions

    • Benzodiazepines: Useful in foals but avoided in adult horses due to panic response and muscle weakness

Standing Sedation Procedure

Pre-Sedation Preparations

  • Conduct a physical exam to assess suitability for standing procedure

  • Preparation includes setting up stocks and infusion stands, and preparing medications

  • Methodical monitoring: ECG, blood pressure, and clinical evaluation

  • Ensure cooperative behavior from the horse to facilitate the standing procedure

Analgesia Management

  • Ensure adequate pain control with NSAIDs and local anesthetics (e.g., lidocaine, mepivacaine)

  • Adjust analgesic agents according to surgical requirements

Induction of General Anesthesia

Induction Techniques

  1. Swing Gate: Typically used in clinical settings, involving a padded wall to help control horse descent

  2. Field Induction: Not advisable for heavy horses, relies more on manual assistance

  3. Drugs Used: Ketamine combined with benzodiazepines; alternative drugs offer poor quality induction and recovery

Maintenance Strategies

  • Options include:

    • Total intravenous anesthesia (TIVA)

    • Inhalation anesthesia (requires ventilation)

    • Partially intravenous anesthesia (PIVA) which combines both types for reduced inhalant exposure

Monitoring During Anesthesia

Essential Monitoring Parameters

  • Ensure tissue oxygenation and adequate ventilation

  • Monitoring tools: ECG, invasive blood pressure, pulse oximetry, capnography, arterial blood gas analysis

  • Aim to keep blood pressure above 70 mmHg to reduce myopathy risk in horses

Oxygen Optimization Techniques

  • Manage arterial carbon dioxide levels, particularly in cases of hypoventilation

  • Implement PEEP to maintain alveoli open and optimize ventilation

Recovery Phase

Key Considerations

  • Administer alpha-2 top-ups to ensure calmness during recovery

  • Monitor for nasal edema, be prepared for assisted recovery if needed

  • Evaluate options for free recovery versus assisted recovery depending on horse condition

Complications in Recovery

  • Common complications include trauma, respiratory obstruction, fractures, and myopathies

  • Monitor carefully for signs of discomfort, and perform interventions to support recovery

Conclusion and Ethical Considerations

  • Remember the implications of anesthetic practices on animal welfare and food safety

  • Consider environmental impacts of anesthetic agents and gas flows used in procedures

Final Thoughts

  • Successful equine anesthesia involves understanding anatomy, pharmacology, and collaboration among all team members involved.

  • The content covered serves as a foundational guide for understanding and applying the principles of equine sedation and anesthesia effectively.