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Questions and Answers
What is a common factor that contributes to post-operative colic in horses after general anaesthesia?
What genetic condition is characterized by a defective sodium channel in the muscle membrane?
Which treatment is essential for managing hyperkalaemic periodic paralysis in affected horses?
What complication can arise if an IV catheter is directed downwards?
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What effect do α2-agonists have during the recovery phase from anaesthesia in horses?
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Which of the following complications can occur following orthopaedic surgery in horses?
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What can be a consequence of severe sedative effects during recovery from anaesthesia?
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Which type of horse is particularly affected by hyperkalaemic periodic paralysis?
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What is the primary purpose of oxygen supplementation during recovery from anesthesia in horses?
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Which characteristic is NOT essential for an ideal recovery box for horses?
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In which position is a horse’s left lung ideally placed for optimal oxygenation during recovery?
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Which anesthetic agent is commonly administered in conjunction with NSAIDs during recovery for pain management?
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What should be avoided in the design of a recovery box for horses?
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Which of the following is a recommended method to allow oxygen administration to apnoeic horses?
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What is an ideal floor characteristic for a horse's recovery box?
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In emergency situations during recovery, which feature should be included in a recovery box for immediate response?
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What temperament characteristic of horses can lead to rough recoveries post-anesthesia?
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Which method is typically preferred for induction in adult horses?
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Which factor significantly affects recovery challenges in equine anesthesia?
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How do isoflurane and halothane compare regarding mortality risk?
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Why is food restriction important prior to anesthesia in horses?
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What is a key consideration for health status prior to surgery in horses?
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What is recommended preparation before horse anesthesia to ensure safety?
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What precaution should be taken regarding the induction area for anesthesia?
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What is a possible complication of lengthy anesthesia in horses, particularly in dorsal recumbency?
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Which method can help manage nasal obstruction in horses recovering from anesthesia?
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What is a key action to take if laryngeal damage is suspected during recovery?
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What can occur if upper airway obstruction is not properly managed during recovery?
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Which of the following is a method to allow oxygen supplementation post-extubation?
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What is the primary indicator of anaesthesia depth in horses, as opposed to heart rate?
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Which of the following is a common cause of hypoxaemia during anaesthesia in horses?
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What is the recommended mean arterial blood pressure (MAP) to maintain during general anaesthesia in horses?
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In horses under anaesthesia, what physiological change may occur in response to high sympathetic nervous system output?
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What common respiratory issue can occur specifically in horses in dorsal recumbency during anesthesia?
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What is a common clinical sign associated with the myopathy in horses?
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Which treatment option is recommended for promoting muscle vasodilation in horses with myopathy?
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What condition is likely to be associated with a reluctance to move and myoglobinuria in horses?
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What is a common contributing factor for developing peripheral neuropathies during anesthesia?
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Which option is a method to reduce muscle swelling in horses with myopathy?
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What is a potential complication of using α2-agonists in animals?
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Which statement about xylazine's analgesic effects is correct?
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What should be administered following severe bradycardia resulting from α2-agonist use?
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Which group of animals is particularly sensitive to α2-agonists and requires lower dosages?
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What is the purpose of vatinoxan in relation to α2-agonists?
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What effect do α2-agonists have on respiratory function?
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When using atipamezole in horses, what is a key consideration?
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What factor increases the anesthetic risk for larger horses?
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What is a primary reason foals younger than 1 month old have higher mortality rates?
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Which drug should be avoided in the sedation of foals less than 1 month old due to their cardiovascular immaturity?
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How do the lungs of neonates differ from adults in terms of compliance?
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What condition can develop in foals due to their reduced ability to excrete water?
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What should be avoided to reduce the risk of gastrointestinal ulcers in foals younger than 6 weeks?
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Which method is used for induction of anaesthesia in foals?
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What is a common sign of gastrointestinal ulceration in foals?
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What is crucial for a foal's recovery post-anaesthesia?
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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.
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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.
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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.
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Possible contributing factors:
- Pain
- Stress of travel or hospitalization
- Starvation
- Other drugs like alpha-2 agonists or anti-muscarinic drugs.
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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.
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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.
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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).
IV Catheter-Related Problems
-
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
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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.
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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
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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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Description
This quiz explores the unique health considerations and temperament traits associated with various horse breeds. It discusses the specific risks that different breeds, such as Draught horses and Quarter horses, face during recovery. Additionally, it examines the effects of age, sex, and temperament on horse recovery and care.
