9. Equine Anesthesia


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  • The same anesthetic principles apply to both small animal and equine surgery as well as patient preparation essentials (Chapters 2 and 8).
  • IM induction is not used in horses except to capture feral horses.
  • Horses don’t regurgitate during anesthesia so not all animals need to be intubated during anesthesia. Field anesthesia rarely includes intubating the horse.
  • Dobutamine, a positive inotrope, is used to treat hypotension in horses.
  • 9. Equine Anesthesia

    1. 1. Equine Anesthesia Chapter 9
    2. 2. What Makes Equine Anesthesia Uniquely Challenging? <ul><li>Temperament </li></ul><ul><ul><li>Wide variety of temperaments </li></ul></ul><ul><ul><ul><li>Calm and stoic to excitable and nervous </li></ul></ul></ul><ul><ul><li>Flight animals exhibit unpredictable behavior </li></ul></ul><ul><ul><li>Instinctive desire to stand shortly after awakening from anesthesia </li></ul></ul><ul><li>Equipment </li></ul><ul><ul><li>Horses are big animals and require specialized restraint and anesthetic equipment </li></ul></ul>
    3. 3. What Makes Equine Anesthesia Uniquely Challenging? (Cont’d) <ul><li>Anatomy and Physiology </li></ul><ul><ul><li>Obligate nasal breathers </li></ul></ul><ul><ul><li>Large, heavy GI tract pressing on lungs can produce atelectasis </li></ul></ul><ul><ul><li>Neuropathy and myopathy with inadequate padding </li></ul></ul>
    4. 4. Selecting an Anesthetic Protocol <ul><li>Factors to consider </li></ul><ul><ul><li>Minimum patient database </li></ul></ul><ul><ul><li>Patient physical status class </li></ul></ul><ul><ul><li>Type and duration of procedure </li></ul></ul><ul><ul><li>Location </li></ul></ul><ul><ul><ul><li>Field anesthesia (TIVA) </li></ul></ul></ul><ul><ul><ul><li>In-hospital anesthesia (TIVA, injectable induction and inhalation maintenance) </li></ul></ul></ul>
    5. 5. Equine General Anesthesia <ul><li>Equipment preparation </li></ul><ul><ul><li>Make sure all equipment is present before induction begins </li></ul></ul><ul><ul><li>Check the circle system and the ventilator of the anesthetic machine </li></ul></ul><ul><ul><li>Make warming equipment available for small horses and foals </li></ul></ul><ul><ul><li>Crash cart for emergency drugs and equipment </li></ul></ul>
    6. 6. Equine General Anesthesia (Cont’d) <ul><li>Premedication or sedation </li></ul><ul><ul><li>Tranquilizers, alpha 2 -agonists and opioids are given IM or IV </li></ul></ul><ul><ul><li>Anticholinergic drugs reduce gastrointestinal motility, which may result in colic </li></ul></ul>
    7. 7. Large Animal Anesthetic Machine
    8. 8. Equine General Anesthesia <ul><li>Preanesthetic procedure </li></ul><ul><ul><li>Place IV catheter in jugular vein (may have to sedate the horse first) </li></ul></ul><ul><ul><li>Wash mouth to remove feed material </li></ul></ul><ul><ul><li>Feet cleaned and shoes removed or wrapped </li></ul></ul><ul><ul><li>Place patient in induction area or adjacent to tilt table </li></ul></ul>
    9. 9. Preparing a Horse for General Anesthesia
    10. 10. Standing Chemical Restraint <ul><li>A continuation or extension of sedation </li></ul><ul><ul><li>Patient is placed in stocks with cross-ties to keep head in neutral position </li></ul></ul><ul><ul><li>General anesthesia is not desired </li></ul></ul><ul><ul><li>Horse remains standing with drooping lower lip, reluctance to move, wide-based stance, lack of interest in surrounding activity </li></ul></ul><ul><ul><ul><li>Head and neck lower if possible </li></ul></ul></ul><ul><ul><li>May be sensitive to sudden loud noises or movements </li></ul></ul><ul><ul><li>Patient may have to have additional sedative </li></ul></ul>
    11. 11. Standing Chemical Restraint (Cont’d)
    12. 12. Anesthetic Induction <ul><li>Goal </li></ul><ul><ul><li>Render the horse unconscious as quickly as possible so that the transition from standing (sedated) to lateral recumbency (unconscious) occurs with minimal risk of injury </li></ul></ul><ul><li>Induction drugs </li></ul><ul><ul><li>Administered by rapid bolus injection rather than “to effect” (except guaifenesin) </li></ul></ul><ul><ul><li>IV injectables such as ketamine alone or in combination with other drugs (diazepam, midazolam) </li></ul></ul><ul><ul><li>Rapid IV guaifenesin (muscle relaxant) to effect followed by ketamine bolus </li></ul></ul>
    13. 13. Anesthetic Induction (Cont’d) <ul><li>After induction check vital signs and intubate immediately </li></ul><ul><li>Position </li></ul><ul><ul><li>Place animal on table and pad superficial nerves and muscle groups </li></ul></ul><ul><ul><li>Forelimb closest to table is pulled forward; separate hindlimbs with padding </li></ul></ul><ul><li>Anesthesia will last 10-20 minutes </li></ul>
    14. 14. Hoisting a Horse after Induction
    15. 15. Correct Padding on a Surgery Table
    16. 16. Inhalation Induction via Nasotracheal Tube <ul><li>Inhalant induction used on young foals </li></ul><ul><li>Endotracheal (ET) tube passes from nostril into ventral nasal meatus and emerges in nasopharynx </li></ul><ul><li>ET tube connected to a small animal anesthetic machine </li></ul><ul><li>Oxygen and inhalant anesthetic are administered </li></ul><ul><li>Risks </li></ul><ul><ul><li>Same as for mask induction in small animals </li></ul></ul>
    17. 17. Equipment for Endotracheal Intubation <ul><li>Endotracheal tubes (at least two of slightly different diameters) </li></ul><ul><li>Mouth gag </li></ul><ul><li>60-mL syringe </li></ul><ul><li>Gauze sponge to grasp tongue (optional) </li></ul>
    18. 18. Equipment for Endotracheal Intubation (Cont’d)
    19. 19. Selecting and Preparing an Endotracheal Tube <ul><li>Use same principles as for small animal selection </li></ul><ul><ul><li>Adult horses: 22-mm, 26-mm, or 30-mm-diameter cuffed tube </li></ul></ul><ul><ul><li>Foals: smaller tubes but not smaller than 10-mm diameter </li></ul></ul><ul><ul><li>Length is usually not an issue </li></ul></ul><ul><li>Preparation </li></ul><ul><ul><li>Prior to use check tubes for blockages, holes, deterioration, other damage </li></ul></ul><ul><ul><li>Connector is securely attached; cuff inflates and holds pressure after detaching syringe </li></ul></ul><ul><ul><li>Tube is clean and sanitized </li></ul></ul>
    20. 20. Equine Intubation <ul><li>Orotracheal intubation </li></ul><ul><ul><li>Performed blindly by feel </li></ul></ul><ul><ul><ul><li>Placement in esophagus is rare </li></ul></ul></ul><ul><ul><li>Extend head and pull tongue to one side; insert mouth gag </li></ul></ul><ul><ul><li>Pass ET tube through gag, over base of tongue, into larynx </li></ul></ul><ul><ul><li>Advance tube into the trachea (no resistance present) </li></ul></ul><ul><ul><li>Confirm placement by feeling air movement when horse exhales </li></ul></ul><ul><ul><li>Tie tube to mouth gag or tape to horses muzzle </li></ul></ul><ul><ul><li>Inflate the cuff </li></ul></ul>
    21. 21. Equine Intubation (Cont’d) <ul><li>Nasotracheal intubation </li></ul><ul><ul><li>For surgeries of the head and neck </li></ul></ul><ul><ul><li>Tube is passed into the ventral nasal meatus and through to the trachea </li></ul></ul>
    22. 22. Complications of Intubation <ul><li>Similar to those in small animal intubation </li></ul><ul><li>Additional concerns </li></ul><ul><ul><li>Epistaxis from nasal intubation </li></ul></ul><ul><ul><li>Abnormal anatomy may cause difficult intubation </li></ul></ul><ul><ul><ul><li>Miniature horses </li></ul></ul></ul><ul><ul><ul><li>Oral and nasal cavity diseases </li></ul></ul></ul><ul><ul><ul><li>Laryngeal paralysis </li></ul></ul></ul>
    23. 23. Anesthetic Maintenance with an Inhalant Agent <ul><li>Similar to maintenance in small animals, with the following exceptions: </li></ul><ul><ul><li>Changes in inhalant anesthetic and oxygen flow rate occur slowly </li></ul></ul><ul><ul><li>Altering machine settings may not bring patient back to surgical anesthesia </li></ul></ul><ul><ul><li>Thiopental or ketamine IV are used to return patient to surgical anesthesia </li></ul></ul>
    24. 24. Anesthetic Maintenance with an Inhalant Agent (Cont’d) <ul><li>Horses are more likely to develop: </li></ul><ul><ul><li>Hypoventilation </li></ul></ul><ul><ul><ul><li>Seen with dorsal recumbency </li></ul></ul></ul><ul><ul><ul><li>Mechanical ventilation often used </li></ul></ul></ul><ul><ul><li>Hypotension (arterial blood pressure <70 mm Hg) </li></ul></ul><ul><ul><ul><li>Contributes to myopathy. </li></ul></ul></ul><ul><ul><li>Hypoxemia (PaO 2 < 80 mm Hg) </li></ul></ul><ul><ul><ul><li>More common in horses that are obese, pregnant, have twisted intestines, and are in dorsal recumbency </li></ul></ul></ul>
    25. 25. Direct Blood Pressure Monitoring
    26. 26. Anesthetic Maintenance with Intravenous Agents <ul><li>TIVA for procedures lasting <1 hour and for field anesthesia </li></ul><ul><li>Triple drip </li></ul><ul><ul><li>Combination of guaifenesin, ketamine, and xylazine (or any other alpha 2 -agonist) </li></ul></ul><ul><li>Produces higher blood pressure, less respiratory depression, and more active palpebral reflexes </li></ul><ul><li>Good quality recovery </li></ul><ul><li>Anesthesia extended with additional doses of an alpha 2 -agonist and ketamine </li></ul>
    27. 27. Anesthetic Maintenance with Injectable and Inhalant Agents <ul><li>Triple dip infused at a very slow rate and inhalant anesthesia </li></ul><ul><ul><li>Reduces amount of inhalant agent needed </li></ul></ul><ul><ul><li>Provides muscle relaxation </li></ul></ul><ul><ul><li>Provides analgesia </li></ul></ul><ul><li>Lidocaine or detomidine infusions and inhalant anesthesia </li></ul><ul><ul><li>Decrease inhalant agent requirement </li></ul></ul><ul><ul><li>Provide analgesia </li></ul></ul>
    28. 28. Patient Positioning, Comfort, and Safety <ul><li>Similar to small animal consideration </li></ul><ul><li>Additional concerns </li></ul><ul><ul><li>Control head to protect eyes during induction </li></ul></ul><ul><ul><ul><li>Horses fall and are prone to corneal scrapes </li></ul></ul></ul><ul><ul><li>Apply hobbles correctly when hoisting animals </li></ul></ul><ul><ul><ul><li>Incorrectly applied hobbles will allow the animal to fall from hoist </li></ul></ul></ul><ul><ul><li>Padding and positioning on the surgery table </li></ul></ul><ul><ul><ul><li>To prevent neuropathies and myopathies </li></ul></ul></ul>
    29. 29. Anesthetic Recovery <ul><li>Psychologic need to stand up shortly after awakening from anesthesia </li></ul><ul><li>Obligate nasal breathers </li></ul><ul><li>Recovery dangerous for the horse and anesthetist </li></ul><ul><li>High incidence of complications can be minimized </li></ul><ul><ul><li>Specific padded areas or rooms dedicated as recovery stalls </li></ul></ul><ul><ul><li>Prevent horse from standing too soon </li></ul></ul>
    30. 30. Preparation for and Monitoring Recovery <ul><li>When the procedure is completed </li></ul><ul><ul><li>Replace halter and attach assist rope </li></ul></ul><ul><ul><li>Attach rope to tail </li></ul></ul><ul><ul><li>Place nasopharyngeal tube if necessary </li></ul></ul><ul><ul><li>Turn off inhalant </li></ul></ul><ul><ul><li>Transfer patient to padded recovery area </li></ul></ul><ul><ul><li>Provide oxygen support if necessary </li></ul></ul><ul><ul><ul><li>Demand valve or insufflation </li></ul></ul></ul>
    31. 31. Preparation for and Monitoring Recovery (Cont’d) <ul><li>Monitoring a recovering patient </li></ul><ul><ul><li>Anesthetist should monitor continually and stay by the head </li></ul></ul><ul><ul><li>Watch respirations for normal breathing </li></ul></ul><ul><ul><li>Take pulse every 5-10 minutes </li></ul></ul><ul><ul><li>Assess eye for anesthetic depth </li></ul></ul><ul><ul><li>Be prepared for extubation or to control horse if it attempts to stand too soon </li></ul></ul>
    32. 32. Rope Placement for Assisted Recovery
    33. 33. Assisted Anesthetic Recovery Using Ropes
    34. 34. Anesthetist Restraining a Horse
    35. 35. Nasopharyngeal Tube Placed for Recovery
    36. 36. Signs of Recovery and Extubation <ul><li>Nystagmus (rapid) with paddling of limbs </li></ul><ul><ul><li>Can indicate horse will attempt to get up too soon </li></ul></ul><ul><ul><li>May have to sedate with xylazine IV or acepromazine IV </li></ul></ul><ul><ul><li>Control head by sitting on the neck or holding the head off the floor </li></ul></ul>
    37. 37. Signs of Recovery and Extubation (Cont’d) <ul><li>Extubation </li></ul><ul><ul><li>Chewing, swallowing, purposeful ear, or limb or tail movement means animal is ready </li></ul></ul><ul><ul><li>Deflate cuff </li></ul></ul><ul><ul><li>Remove tube in a slow, steady motion </li></ul></ul><ul><ul><li>Check for normal breathing </li></ul></ul><ul><ul><li>Check for obstruction leading to distress </li></ul></ul>
    38. 38. Standing after Regaining Consciousness <ul><li>Ideal recovery </li></ul><ul><ul><li>Horse is extubated </li></ul></ul><ul><ul><li>Rolls smoothly from lateral to sternal recumbency </li></ul></ul><ul><ul><li>After a few minutes stands in one try </li></ul></ul><ul><ul><li>Head and tail ropes may be used </li></ul></ul><ul><li>Complicated recovery </li></ul><ul><ul><li>Horse may attempt to stand too soon </li></ul></ul><ul><ul><li>May need sedation, analgesia, or physical restraint to prevent injury </li></ul></ul><ul><ul><li>May suffer catastrophic event (e.g., fractured bone) </li></ul></ul>
    39. 39. Postanesthetic Period <ul><li>Return horse to stall when it is able to walk steadily </li></ul><ul><li>Muzzle for 1-3 hours but provide free access to water </li></ul><ul><li>Observe for signs of neuropathy </li></ul><ul><ul><li>Facial nerve paralysis </li></ul></ul><ul><ul><ul><li>Drooping eyelid and lip on the affected side </li></ul></ul></ul><ul><ul><li>Radial nerve paralysis </li></ul></ul><ul><ul><ul><li>Inability to fully extend affected forelimb </li></ul></ul></ul>
    40. 40. Postanesthetic Period (Cont’d) <ul><li>Observe for signs of myopathy </li></ul><ul><ul><li>Hard, swollen muscles, stiff and painful gait </li></ul></ul><ul><li>Observe for signs of colic </li></ul><ul><ul><li>Rolling, kicking at the abdomen </li></ul></ul>