Equine Anesthesia Flashcards
What are the problems associated with equine anesthesia?
Prolonged recumbency
Inadequate muscle blood flow and myostitis
Neuropathy due to poor positioning
Detrimental changes in cardiopulmonary function
Poor oxygenation
What makes induction and recovery difficult and potentially dangerous to the animal and other personnel?
The general temperament and size of the horse
Why do horses sometimes colic after anesthesia for elective surgery?
The depressive effects of anesthetic drugs on gastrointestinal motility
Why should an elective surgery be delayed for a horse that has a cough and intermittent nasal discharge?
The oxygenation and ventilation of the horse may be effected
What separates both sides of the lungs?
The mediastinum
Why is airway patency such a big deal in horses?
Horses are obligate nasal breathers
while going under anesthesia or recovering if the air is not provided by an endotracheal tube, or by other means, the horse could be in respiratory trouble
What ECG system (set-up) is used on horses and other large animals during general anesthesia?
The Base-Apex system
What common physiologic cardiac rhythm variations can be detected in horses?
1st degree heart block 2nd degree heart block Sino-atrial block Variably configured P-waves Atrial fibrilation
What is the most common cardiac arrhythmia of clinical significance in the horse?
Atrial Fibrillation
How is atrial fibrillation diagnosed?
Palpation of irregular pulses with varying strengths
Auscultation
Echocardiogram (abscence of P waves)
Why is rinsing out a horse’s mouth a step taken in the pre-anesthetic preparation?
To remove any foreign material to prevent aspiration
What 3 groups of drugs are commonly used for sedation or pre-medication in horses?
Phenothiazines
Alpha-2 agonists
Opiods
List 5 important facts to know about the use of Acepromazine in horses:
It is a major tranquilizer that produces a calm and relaxed state
It does not produce analgesia
Its onset of action is 15 to 20 minutes and the duration is 6 to 10 hours
Causes hypotension
Not reversible
List 5 important facts to know about the use of Alpha-2 Agonists in horses:
Produces a moderate to profound sedation, analgesia, and muscle relaxation
Can induce or exacerbate first and second-degree heart block
Sedation is characterized by a “head down” posture and some ataxia
Used for temporary relief of colic pain
Used for a pre-medication for general anesthesia and for standing chemical restraint
What Alpha-2 agonists are used in horses?
Xylazine and Detomidine
Is Xylaxine or Detomidine more potent?
Detomidine is 80-100 times more potent than xylazine
What does moderate sedation look like in horses?
Head drooping
What does profound sedation look like in horses?
Head goes to the ground
List 2 important facts to know about the use of Opioids in horses
cause nervousness and excitement in horses.
Why is Butorphanol preferred in horses?
it causes less excitement or ileus than the mu-agonists (morphine)
Why are anticholinergics not routinely used as a pre-anesthetic drug in horses?
it can depress gastrointestinal motility.
What breeds of horses are considered lighweights?
Draft horses and Tennessee Walking horses
What drugs are commonly used in horses as induction agents?
Ketamine with Guaifenesin
Ketamine with Diazepam
Thiobarbiturates +/- Guaifenesin
What are the most commonly used drugs for induction?
Ketamine with Diazepam
What are the common endotracheal tube sizes used in horses?
The most common ET tube size is 26 mm
Smaller breeds 16 mm
Ranges 16-30 mm
How are horses intubated?
Horses are in lateral recumbency with the head straightened out to intubate. A plastic gag is used to protect the tube from the teeth, and then the tube is blindly passed into the larynx.
What is TIVA?
Total Intravenous Anesthesia
What drugs are commonly used with TIVA and are known as “Triple Drip”
Guaifenesin
Ketamine
Xylazine
Name three ways local anesthesia may be used in horses.
nerve block, field block, or epidural anesthesia
What three classes of drugs can be used for caudal epidural anesthesia?
Alpha-2 agonists, opioids, and local anesthesia
Why is nitrous oxide not recommended in inhalant anesthesia for horses?
alveolar collapse and hypoxia in horses that are recumbent
Which large muscle groups are commonly involved in Compartment syndrome?
Gluteals, Triceps, Masseters, and Quadriceps
Besides muscle and nerve injury, what other organ is often affected by Compartment syndrome
The kidneys
Why are the kidneys affected by Compartment Syndrome?
Compartment syndrome causes acute renal failure from the damage to the kidney tubules from myoglobin, which is released from damaged skeletal muscle cells.
When placing a horse in lateral recumbency for surgery under general anesthesia, what are important things to ensure when positioning?
elevated the head to prevent nasal edema
support the upper limbs
pull the lowermost forelimb
Why is the lowermost fore limb pulled when in lateral recumbency?
To prevent a neuropathy in the radial nerve
When placing a horse in dorsal recumbency for surgery under general anesthesia, what are important things to ensure when positioning?
elevated the head do not overextend the head support and restrain the limbs no leg stretching have the horse centered on the mattress
When monitoring horses under general anesthesia, what 5 things can be assessed to determine the depth of anesthesia?
dull palpebral reflexes, strong corneal reflex, moist (not tearing) eyes, no nystagmus and no spontaneous blinking
What should the MAP be for a horse under GA?
70 mm Hg or greater
How is blood pressure usually monitored in horses?
intraarterial catheter and a pressure transducer
Why does hypoventilation commonly affect horses?
because of their size and the weight of their lungs, which leads to ventilation/perfusion mismatch.
What is ventilation/perfusion mismatch?
When parts of the lungs that are well oxygenated do not correspond to the parts of the lungs that are well perfused with blood
What are the ideal conditions and steps for recovering horses from GA?
Recover in lateral recumbency
Without encouragement to try and stand before drugs have time to wear off
When does recovery happen best for horses?
When it is allowed to rest quietly until it decides to get up on its own
Why is nasal edema an issue in horses?
It may severely compromise breathing and warrant immediate treatment
How is nasal edema treated?
Head elevated with the nose tilted slightly higher than the rest of the head
Nasotracheal tube should be placed
What are some benefits of standing surgery (versus GA)?
The primary benefit of standing surgery is avoiding the risks of GA, specifically recovery
It is easier to perform on a standing patient for anatomic or physiologic reasons
What is the largest risk for surgical patients?
Recovery from GA
Why are intact male horses castrated?
To reduce or prevent sexual behavior and aggressive behavior
Preventing reproduction of horses that have inferior or undesirable genetic traits
To treat certain malignant diseases, testicular trauma, inguinal or scrotal hernias
How is castration commonly performed?
done in the field, using an emasculator, with the horse either standing or recumbent
What is the difference between Closed and Open castration?
closed castration is when the spermatic cord and vaginal tunic are emasculated, which leads to more bleeding and a greater chance that a vessel will emasculate improperly.
Open castration is when an incision is made over each testicle to dissect out the testis and the spermatic cord. The spermatic cord is crushed with the emasculators and the testicles are torn away
What are post-operative complications associated with castrations?
severe hemorrhaging, excessive swelling from inadequate drainage, acute wound infection, septicemia, protrusion of abdominal viscera, and persistent masculine behavior.
What are 3 different surgical approaches for cryptorchidectomy?
extract the testicle from the incision, using fingers or sponge forceps and emasculate the spermatic cord.
Inguinal approach.
Paramedian approach
What is the inguinal approach for cryptorchidectomy?
The incision site is packed with gauze soaked in an antiseptic
Removed 1 to 3 days after surgery
What is the Paramedian approach to cryptorchidectomy?
Incision is closed with a suture
What is Caslick’s procedure?
pneumovagina repair due to poor conformation, injury, breeding, and foaling
What is Caslick’s procedure performed?
To prevent fecal material from entering the vagina when the vulva does not form a perfect seal
What are some commonly performed MIS in horses?
arthroscopy for osteochondral chip fractures and OCD lesions, and upper airway surgery.
Why would an abdominal exploratory be performed in horses?
When colic is suspected
What horse breeds would be prime candidates for eye tattoos?
Paints and Appaloosas
Myostitis is due to what?
Poor positioning, padding and hypotension
What are the clinical signs of myositis?
Paralysis and weakness on attempts to stand
Hard muscles on palpation
Myoglobinuria
High creatine phosphokinase
How do you treat myositis?
IVF to help with perfusion
Ace for peripheral perfusion
NSAIDs for analgesia or Opioids if the kidneys are affected
+/- DMSO
How do you prevent myopathy and neuropathy?
Proper positioning of limbs and head during maintenance and recovery Remove halter Maintain MAP at 70 mmHg Avoid ischemia and reperfusion injury Promote venous return Avoid overextension and overstretching
