Horse Breed Considerations for Care
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Questions and Answers

What is a common factor that contributes to post-operative colic in horses after general anaesthesia?

  • Overexertion during recovery
  • Increased muscle mass
  • Pain (correct)
  • Excessive water intake

    • What genetic condition is characterized by a defective sodium channel in the muscle membrane?

  • Myotonia congenita
  • Congenital myopathy
  • Hypokalemic periodic paralysis
  • Hyperkalaemic periodic paralysis (correct)

    • Which treatment is essential for managing hyperkalaemic periodic paralysis in affected horses?

  • Intensive physical therapy
  • Continuous furosemide infusion
  • Prokinetic agents or analgesics (correct)
  • Immediate surgery

    • What complication can arise if an IV catheter is directed downwards?

    <p>Air embolism</p> Signup and view all the answers

    What effect do α2-agonists have during the recovery phase from anaesthesia in horses?

    <p>They facilitate elimination of anaesthetic drugs</p> Signup and view all the answers

    Which of the following complications can occur following orthopaedic surgery in horses?

    <p>Pulmonary microemboli</p> Signup and view all the answers

    What can be a consequence of severe sedative effects during recovery from anaesthesia?

    <p>Increased risk of ataxia</p> Signup and view all the answers

    Which type of horse is particularly affected by hyperkalaemic periodic paralysis?

    <p>Appaloosas</p> Signup and view all the answers

    What is the primary purpose of oxygen supplementation during recovery from anesthesia in horses?

    <p>To support muscle contraction necessary for recovery</p> Signup and view all the answers

    Which characteristic is NOT essential for an ideal recovery box for horses?

    <p>Multiple levels for the horse to climb</p> Signup and view all the answers

    In which position is a horse’s left lung ideally placed for optimal oxygenation during recovery?

    <p>Left lateral recumbency</p> Signup and view all the answers

    Which anesthetic agent is commonly administered in conjunction with NSAIDs during recovery for pain management?

    <p>α2-agonists</p> Signup and view all the answers

    What should be avoided in the design of a recovery box for horses?

    <p>Corners for structural support</p> Signup and view all the answers

    Which of the following is a recommended method to allow oxygen administration to apnoeic horses?

    <p>Use of an oxygen demand valve</p> Signup and view all the answers

    What is an ideal floor characteristic for a horse's recovery box?

    <p>Well padded and compressible floor</p> Signup and view all the answers

    In emergency situations during recovery, which feature should be included in a recovery box for immediate response?

    <p>Escape route for staff</p> Signup and view all the answers

    What temperament characteristic of horses can lead to rough recoveries post-anesthesia?

    <p>Flighty horses may try to stand up quickly and run.</p> Signup and view all the answers

    Which method is typically preferred for induction in adult horses?

    <p>Injectable options are usually preferred for adults.</p> Signup and view all the answers

    Which factor significantly affects recovery challenges in equine anesthesia?

    <p>Long surgical procedures increase recovery time and complications.</p> Signup and view all the answers

    How do isoflurane and halothane compare regarding mortality risk?

    <p>Both agents show no major differences concerning mortality risk.</p> Signup and view all the answers

    Why is food restriction important prior to anesthesia in horses?

    <p>Avoiding a large stomach reduces the risk of compression atelectasis.</p> Signup and view all the answers

    What is a key consideration for health status prior to surgery in horses?

    <p>Sick animals present a higher mortality risk during anesthesia.</p> Signup and view all the answers

    What is recommended preparation before horse anesthesia to ensure safety?

    <p>A complete clinical history and necessary blood work should be done.</p> Signup and view all the answers

    What precaution should be taken regarding the induction area for anesthesia?

    <p>Ensure the area is padded and safe for the horse.</p> Signup and view all the answers

    What is a possible complication of lengthy anesthesia in horses, particularly in dorsal recumbency?

    <p>Nasal mucosae edema due to vascular congestion</p> Signup and view all the answers

    Which method can help manage nasal obstruction in horses recovering from anesthesia?

    <p>Applying a topical vasoconstrictor in the nose</p> Signup and view all the answers

    What is a key action to take if laryngeal damage is suspected during recovery?

    <p>Recover the horse with the endotracheal tube in place</p> Signup and view all the answers

    What can occur if upper airway obstruction is not properly managed during recovery?

    <p>Development of pulmonary edema with pink frothy fluid</p> Signup and view all the answers

    Which of the following is a method to allow oxygen supplementation post-extubation?

    <p>Inserting a nasopharyngeal tube</p> Signup and view all the answers

    What is the primary indicator of anaesthesia depth in horses, as opposed to heart rate?

    <p>Blood pressure</p> Signup and view all the answers

    Which of the following is a common cause of hypoxaemia during anaesthesia in horses?

    <p>Low inspired FiO2</p> Signup and view all the answers

    What is the recommended mean arterial blood pressure (MAP) to maintain during general anaesthesia in horses?

    <p>70 mmHg</p> Signup and view all the answers

    In horses under anaesthesia, what physiological change may occur in response to high sympathetic nervous system output?

    <p>Increased stroke volume</p> Signup and view all the answers

    What common respiratory issue can occur specifically in horses in dorsal recumbency during anesthesia?

    <p>Hypoxaemia and hypercapnia</p> Signup and view all the answers

    What is a common clinical sign associated with the myopathy in horses?

    <p>Swollen, painful muscles</p> Signup and view all the answers

    Which treatment option is recommended for promoting muscle vasodilation in horses with myopathy?

    <p>Acepromazine 0.03 mg/kg IM or IV</p> Signup and view all the answers

    What condition is likely to be associated with a reluctance to move and myoglobinuria in horses?

    <p>Hyperkalaemic periodic paralysis</p> Signup and view all the answers

    What is a common contributing factor for developing peripheral neuropathies during anesthesia?

    <p>Inadequate surgical padding</p> Signup and view all the answers

    Which option is a method to reduce muscle swelling in horses with myopathy?

    <p>Topical steroidal creams</p> Signup and view all the answers

    What is a potential complication of using α2-agonists in animals?

    <p>Severe tissue hypoperfusion</p> Signup and view all the answers

    Which statement about xylazine's analgesic effects is correct?

    <p>It provides greater analgesia possibly due to α1-agonist effects.</p> Signup and view all the answers

    What should be administered following severe bradycardia resulting from α2-agonist use?

    <p>An antagonist followed by an anticholinergic</p> Signup and view all the answers

    Which group of animals is particularly sensitive to α2-agonists and requires lower dosages?

    <p>Large breeds</p> Signup and view all the answers

    What is the purpose of vatinoxan in relation to α2-agonists?

    <p>To prevent cardiovascular effects of α2-agonists</p> Signup and view all the answers

    What effect do α2-agonists have on respiratory function?

    <p>Prolong sedation leading to nasal obstruction</p> Signup and view all the answers

    When using atipamezole in horses, what is a key consideration?

    <p>It can reverse analgesic effects along with unwanted complications.</p> Signup and view all the answers

    What factor increases the anesthetic risk for larger horses?

    <p>Greater likelihood of reduced GI motility</p> Signup and view all the answers

    What is a primary reason foals younger than 1 month old have higher mortality rates?

    <p>Less mature physiological functions</p> Signup and view all the answers

    Which drug should be avoided in the sedation of foals less than 1 month old due to their cardiovascular immaturity?

    <p>α2-agonists</p> Signup and view all the answers

    How do the lungs of neonates differ from adults in terms of compliance?

    <p>Neonates have stiffer lungs than adults</p> Signup and view all the answers

    What condition can develop in foals due to their reduced ability to excrete water?

    <p>Hypervolaemia</p> Signup and view all the answers

    What should be avoided to reduce the risk of gastrointestinal ulcers in foals younger than 6 weeks?

    <p>NSAIDs</p> Signup and view all the answers

    Which method is used for induction of anaesthesia in foals?

    <p>Ketamine combined with benzodiazepine</p> Signup and view all the answers

    What is a common sign of gastrointestinal ulceration in foals?

    <p>Dorsal recumbency</p> Signup and view all the answers

    What is crucial for a foal's recovery post-anaesthesia?

    <p>Ensuring it can walk and maintain balance</p> Signup and view all the answers

    Study Notes

    Horse Breed Considerations

    • Draught horses: Higher risk of developing spinal cord malacia (softening) and myopathy (muscle disease)
    • Quarter horses: Susceptible to hyperkalaemic periodic paralysis (a condition characterized by high potassium levels in the blood)
    • Welsh ponies: High prevalence of ventricular septal defects (a hole in the wall separating the heart chambers)
    • Thoroughbreds: Higher risk of fractures during recovery due to their fitness and temperament

    Temperament

    • Flighty horses: Have an increased risk of rough recoveries due to their tendency to quickly rise and run.

    Sex

    • Stallions: May experience rough recoveries or develop priapism (prolonged erection) with alpha-2 agonists.
    • Pregnant mares: Are sensitive to alpha-2 agonists (a class of drugs that can cause sedation and muscle relaxation).

    Age

    • Young animals: Have an immature physiology and are at a higher risk of hypothermia (low body temperature).
    • Older horses: Higher chances of osteoporosis (thinning of the bones) and muscle weakness during recovery.

    Surgical Time

    • Long procedures: Lead to longer recoveries and increased chances of complications.

    Time of Day

    • Out-of-hours procedures: May result in less available staff, junior untrained staff, and fatigue.

    Anaesthetic Agents

    • Lack of premedication: Increases risks for the horse.
    • Acepromazine: Reduces mortality rates in horses undergoing anaesthesia.
    • Isoflurane vs. Halothane: No significant differences in mortality rates between the two inhalant anaesthetics.

    Health Status

    • Sick animals: Have a higher mortality rate during anaesthesia.

    Preparation for Anaesthesia

    • Clinical history and examination: Essential before anaesthesia.
    • Blood work baseline: PCV (packed cell volume) and TP (total protein) should be checked.
    • Food Restriction:
      • Horses are unable to vomit but can regurgitate or develop reflux.
      • Recommended starvation period is 4 to 6 hours prior to anaesthesia with free access to fresh water.
      • Avoiding a large stomach is crucial to prevent:
        • Compression atelectasis (collapsed lung)
        • Stomach rupture when the horse falls during induction.
    • IV catheter: Place a catheter in the jugular vein.
    • Specific theatre head collar: Apply a head collar designed for the operating room.
    • Remove shoes: To protect the box floor and staff.
    • Mouth wash: Remove debris from the mouth.
    • Personal protective equipment: Important for both veterinary staff and the horse.
    • Pre-anaesthetic medications: NSAIDs (nonsteroidal anti-inflammatory drugs) and intravenous antibiotics may be administered.
    • Premedication: Used to calm the horse and prepare it for anaesthesia.

    Induction of Anaesthesia

    • Safe induction area: Essential for safe induction. Should be padded and equipped for the horse's safety.
    • Induction methods:
      • Injectable options are typically used for adults.
      • Inhalant agents are an option for foals.

    Treatment

    • Remove obstruction: Clear any airway obstruction.
    • Clear the airway: Ensure a clear airway for the horse.
    • Furosemide: 1-2 mg/kg intravenously.
    • Dexamethasone: 0.25 mg/kg intravenously.

    Recovery

    Post-operative Colic

    • Mild signs of colic: Frequently reported in horses after general anaesthesia.
    • Opioids: Often blamed for post-operative colic, but no direct evidence supports this.
    • Possible contributing factors:
      • Pain
      • Stress of travel or hospitalization
      • Starvation
      • Other drugs like alpha-2 agonists or anti-muscarinic drugs.
    • Treatment:
      • Prokinetics (drugs that increase stomach motility)
      • Analgesics (painkillers) such as lidocaine infusion.

    Hyperkalaemic Periodic Paralysis (HYPP)

    • Autosomal dominant genetic disease: Affects primarily Appaloosa and Quarter horses.
    • Defective sodium channel in the muscle membrane: Leads to abnormal sodium and potassium movement, resulting in hyperkalaemia (high potassium) and muscle paralysis:
      • Increased influx of sodium ions and efflux of potassium ions.
      • Persistent depolarisation of muscle cells.
      • Generalized muscle weakness (flaccid paralysis).
      • Hyperkalaemia.
    • Recovery: May be prolonged, with the horse often exhibiting a "dog-sitting" position. Can also cause:
      • Laryngeal paralysis.
      • Respiratory muscle weakness (and possible respiratory muscle arrest).
    • Catheter cap dislodged:
      • Upward direction: Haemorrhage (usually not lethal as clotting limits blood loss).
      • Downward direction: Air embolism (leads to itching, pulmonary edema, agitation).
    • Jugular vein thrombosis: Can develop after a few days.

    Pulmonary Microemboli

    • Can develop after orthopaedic surgery: Leads to delayed recovery and can cause:
      • Sweating
      • Distress
      • Tachycardia (rapid heart rate)
      • Tachypnoea (rapid breathing).

    Preventing Recovery Problems

    • Sedation during recovery: Alpha-2 agonists (e.g., romifidine) can extend recumbency, allowing the horse to eliminate anaesthetic drugs and have less ataxia (loss of coordination) when standing.
    • Oxygen supplementation: Especially important if the horse was hypoxaemic (low oxygen level) during anaesthesia.
      • Administered via ETT (endotracheal tube), nasopharyngeal tube, or an oxygen demand valve.
    • Maintain lateral recumbency: Keeps the non-dependent lung open.
    • Consider left-lung dependent position: For horses who were in dorsal recumbency, as the right lung is larger.
    • Sternal recumbency: Ideal for oxygenation, but difficult to achieve.

    Analgesia (Pain Management)

    • Systemic analgesia: NSAIDs, opioids, and alpha-2 agonists.
    • Loco-regional anaesthesia: Involves numbing a specific area of the body.

    Recovery Box

    • Ideal characteristics:
      • Area of 4 to 5 m2.
      • Well-padded, compressible floor and walls.
      • No corners to prevent the potential for the horse to get stuck.
      • Easy to clean and disinfect.
      • Secure doors with floor and ceiling bolts, possibly with restraining bars.
      • Observation window or platform and closed-circuit television.
      • Dimmable lighting and controllable temperature.
      • Close to the operating theatre with access to oxygen and suction sources.
      • Waste anaesthetic gas scavenging.
      • Wall rings for assisted recovery.
      • Access holes in doors to facilitate rope passage.
      • Escape route for staff.
      • Facility for emergency re-anaesthesia.
      • Ceiling hook or winch for a sling.
    • Provides a quiet, darkened, and controlled environment for recovery.

    Xylazine

    • Xylazine is a more potent analgesic than detomidine
    • It also has α1-agonist effects leading to local vasoconstriction
    • The vasoconstriction effect leads to a slower systemic absorption and a higher epidural concentration of the drug, prolonging its effects
    • Dosage: 0.17 – 0.35 mg/kg +/- lidocaine 0.22 mg/kg

    α2-agonist Complications

    • Hypertension and baroreflex bradycardia can occur
    • Bradycardia can be severe, requiring the administration of an antagonist followed by an anticholinergic (atropine, glycopyrrolate or hyoscine)
    • In animals in shock, the cardiovascular effects of α2 agonists may cause severe tissue hypoperfusion
    • Respiratory obstruction due to prolonged sedation and head positioning can cause nasal oedema and obstruction
    • Diuresis can occur due to inhibition of antidiuretic hormone release
    • Sweating, ataxia (muscle weakness or relaxation), increased intrauterine pressure, and reduced GI motility (ileus) can also occur
    • Large breeds are more sensitive to α2 agonists, thus, lower doses must be administered

    α2-agonist Antagonism

    • α2 agonists can be antagonized in case there are unwanted complications
    • Antagonizing the unwanted effects also antagonizes the analgesic effects
    • Atipamezole (0.05 mg/kg IM or slow IV) is used in horses and is an essential drug
    • Vatinoxan is a peripheral α2-receptor antagonist that doesn't cross the blood-brain barrier and prevents the cardiovascular effects of α2-agonists
    • Vatinoxan is only licensed in dogs (Zenalpha®)

    Anaesthesia Risk Factors in Horses

    • Large size:
      • Difficult to handle
      • Increased risk of fractures
      • Higher risks of neuropathy or myopathy
      • Higher risk for the development of hypoxaemia, especially in dorsal recumbency
      • More sensitive to drugs (relative overdose)
      • Accurate weight estimation can be difficult
    • Perineal reflex / anal tone too high indicates too superficial anesthesia
    • Ketamine maintains CNS reflexes

    Cardiovascular Monitoring

    • Susceptible to depression induced by anesthetic agents (particularly volatile agents → cardiovascular support is frequently required)
    • Hypotension is frequent (+++ if inhalant anesthesia and horses in dorsal recumbency)
    • Horses have a large cardiac reserve, so an increase in sympathetic tone may not increase the heart rate. Instead, stroke volume increases.
    • Heart rate is not a good indicator of anesthesia depth in horses, but blood pressure is.
    • To avoid post-anesthetic myopathies, a mean arterial blood pressure (MAP) should remain above 70 mmHg to maintain muscle perfusion during general anesthesia.
    • Padded bed, correct positioning, duration of anesthesia, and use of inodilators (dobutamine) may contribute to reducing the risk of myopathy development

    Respiratory Monitoring

    • Intra-operative hypoxaemia and hypercapnia are common abnormalities in horses under anesthesia, especially in dorsal recumbency
    • Horses have a large respiratory reserve, so an increase in sympathetic nervous system output may not increase respiratory rate, but larger tidal volumes develop.
    • RR is not a good indicator of anesthesia depth in horses, but tidal volume is.
    • Ketamine can induce apneustic breathing (long inspiratory time).
    • Hypoxaemia is caused by:
      • Low inspired FiO2 (failure in supply oxygen; or supply hypoxic mixture)
      • Hypoventilation especially if the horse is not receiving supplemental oxygen (carbon dioxide displaces oxygen in the alveoli reducing its availability to oxygenate blood):
        • Obstruction; malposition of ETT; splinting of the diaphragm; reduced respiratory muscle tone
        • Intraoperative hypotension and hypoxaemia
        • Increased anaesthetic duration (>2h)
        • Fit horses
        • Repeated anaesthetics over a short period of time
        • Hyperkalaemic periodic paralysis (Appaloosas and quarter horses)

    Clinical Signs of Myopathy

    • Affected muscles are hot, swollen, painful, and reduced function
    • Reluctance to move; lameness
    • Myoglobinuria; elevated creatine kinase, aspartate aminotransferase
    • Ataxia, delayed recovery

    Myopathy Treatment

    • Assist horse to stand / provide appropriate padding
    • Light exercise if clinical signs are mild
    • IV fluid therapy (Hartmann’s 4-6 mL/kg/h) to help maintain muscle perfusion and reduce the risk of renal failure due to myoglobinuria
    • Acepromazine 0.03 mg/kg IM or IV to promote muscle vasodilation and improve perfusion + provides anxiolysis
    • NSAIDs +/- opioid +/- α2-agonists for analgesia; α2-agonists provide good sedation but also analgesia
    • Mannitol 0.25 g/kg IV to reduce muscle swelling
    • Dimethyl sulfoxide IV or topically
    • Some practitioners apply steroidal based creams over the affected muscle and apply massage and cold therapy. Ultrasound therapy has also been applied

    Peripheral Neuropathies

    • Similar risk factors to myopathies
    • Poor padding of the surgical table, and inadequate positioning contribute to neuropathies
    • Radial, femoral, peroneal, and facial nerves are mostly affected
    • Hyperflexion/hyperextension of the head and neck = recurrent laryngeal nerve paralysis

    Upper Airway Obstruction: Nasal Passages

    • Horses undergoing lengthy anesthesia, especially in dorsal recumbency, may develop nasal mucosae oedema due to vascular congestion
    • The congestion can be severe enough to obstruct the airway, which is only noticed when the ETT is removed (horses are obligatory nose breathers)
    • Management:
      • Shorter anesthesia duration
      • Allow head position higher than the heart to facilitate venous blood flow
      • Apply topical vasoconstrictor in the nose (Phenylephrine 5 to 10 mg – it is short-acting so timing is important)
      • Place a nasopharyngeal tube: can be placed unilateral or bilaterally, this allows oxygen supplementation after ET removal; and realigns the soft palate with the epiglottis
      • Allowing recovery with the endotracheal tube in place: horses tolerate well the maintenance of ETT in place for recovery; make sure to secure it to the ear / halter and that the cuff is deflated to ensure the horse can breathe if the tube kinks

    Upper Airway Obstruction: Larynx

    • Due to laryngeal damage or paralysis
    • Traumatic ET intubation can damage the arytenoid cartilages or cause oedema
    • Damage to the recurrent laryngeal nerve can also occur and lead to laryngeal obstruction
    • Dorsal displacement of the soft palate and epiglottic retroversion can occur following extubation
    • Recover the horse with the ETT in place if laryngeal issues are anticipated (following laryngeal surgery)
    • If you notice obstruction after extubation: re-intubate (usually nasotracheal); tracheostomy
    • Upper airway obstruction can lead to pulmonary oedema development (pink frothy fluid may come out of the nostrils + cyanotic mucous membranes) – occurs due to excessive airway negative pressure generation to overcome upper airway obstruction.

    Foals

    • Foals > 1 month old = physiological functions similar to adult horses (higher mortality in foals younger than 1 month old)

    Anaesthesia of Foals

    • Consider sedating the dam:
      • If pregnant: detomidine; or another α2-agonist after clenbuterol
    • Foal cardiac output (if neonate):
      • Dependent mostly on heart rate, because the ventricles are less compliant, meaning they cannot expand their volume much
      • Higher pulmonary circulation pressures, may re-open foramen ovale and ductus arteriosus leading to right to left shunt of blood and hypoxaemia.
    • Liver metabolism is immature (prolonged drugs effects; hypoglycaemia; hypothermia)
    • Hypothermia (due to smaller size which causes a larger surface area to body mass ratio = more heat loss); plus, they have little fat reserves (less insulation)

    Neonatal Foals

    • Neonates have a highly compliant chest wall, but poorly compliant or stiff lungs:
      • Results in high work of breathing
      • Because, the intrapleural pressure at end-expiration is equal to the atmospheric pressure as opposed to negative pressure in adults
      • This facilitates airway collapse and low functional residual capacity
      • They are therefore prone to develop hypoxaemia
    • Poor capacity to excrete water in urine → prone to developing hypervolaemia
    • Prone to GI ulcers (stress and poor GI perfusion) (avoid NSAIDs in foals younger than 6 weeks of age. Signs of GI ulceration: bruxism, salivation, dorsal recumbency)

    Sedation in Foals

    • Sedation in foals < 1 month old should avoid α2-agonists due to their immature cardiovascular system that may not cope with lower heart rate
    • Sedation is usually achieved with benzodiazepine and opioid
    • Induction of anaesthesia can be achieved with ketamine + benzodiazepine or propofol or inhalant agent mask induction
    • Maintenance with inhalant anaesthesia as injectable anaesthesia requires heavy metabolism
    • Recovery can be supported by hand
    • Return the foal as quickly as possible to the dam, but make sure the foal is strong enough to walk and maintain its balance

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