Equine Anesthetic Issues

Question 1

Are anticholinergics (atropine, glycopyrrolate) used as preanesthetic drugs for horses?

Answer 1

No

Question 2

What do atropine and glycopyrrolate treat?

Answer 2

Severe bradycardia

Decrease GI motility, gas distention, colic

Question 3

What is acepromazine (tranquilizer) not recommended in? Why?

Answer 3

Stallions

Abnormal erection of penis, tenderness, pain

Question 4

What can diazepam and midazolam (tranquilizers) cause?

Answer 4

Ataxia
Muscle weakness
Recumbency

Question 5

What do sedatives (xylazine, detomidine, dexmedetomidine) cause?

Answer 5

Profound sedation
Analgesia
Muscle relaxation
Bradycardia
Hypertension
Hypotension

Question 6

When can narcotic analgesics be used as preanesthetic drugs?

Answer 6

Only after sedation

Question 7

What do preanesthetic drugs for horses do?

Answer 7

Decrease induction doses
Calming effect, less stress
Provide analgesia
Combined with local techniques for standing anesthesia

Question 8

What are induction considerations?

Answer 8

Horse must be restrained
Premedication (xylazine +/- butorphanol)
Large IV catheter
Draw up more induction drug (ketamine: 200-400 mg total dose)
Rapid induction: ketamine + midazolam

Question 9

What IV technique is preferred for maintenance of general anesthesia?

Answer 9

CRI

Question 10

What is triple drip GKX used for maintenance of general anesthesia?

Answer 10

Xylazine as pred med 15 minutes before
Guaifenesin: 1 L of 5%
Ketamine: 1 mg/ml
Xylazine: 0.5 mg/ml

Question 11

What is the dose of the induction agent for maintenance of general anesthesia?

Answer 11

1 ml/kg IV

Question 12

What is the dose for maintenance of general anesthesia?

Answer 12

2.2 ml/kg/hr IV

Question 13

How long is recovery after 1 hour of anesthesia?

Answer 13

20-25 minutes

Question 14

What are techniques for inhalation anesthesia?

Answer 14

Imapairment of ventilation and oxygenation
Inhalation anesthetics undergo minimal metabolism
Steady plane of anesthesia
Positive pressure ventilation
After premeds, induction, and intubation:
High O2 flow for 15 minutes and then 5 L/min for maintenance
Start IV fluids
Monitoring

Question 15

What causes hypoventilation in horses?

Answer 15

Increased PaCO2 (>40 mmHg) due to reduced minute ventilation

Question 16

What causes hypoxemia in horses?

Answer 16

Decreased PaO2 (<60 mmHg), probably due to V/Q mismatch

Question 17

What is the treatment for hypoventilation?

Answer 17

Mechanical ventilation

Question 18

What is the treatment for hypoxemia?

Answer 18

100% O2 + adequate BP +/- beta agonists (albuterol)

Question 19

What are treatments of hypotension?

Answer 19

Reduce concentration of inhalation anesthetic
Correct dehydration/hypovolemia preoperatively with IV fluids or blood
Inotropes and vasopressors (appropriate fluid volume before):
Ephiderine (12-25 mg)
Dobutamine (1-5 μg/kg/min)
Dopamine (1-10 μg/kg/min)
Calcium gluconate (0.1-0.3 mEq/kg)

Question 20

What can develop from anesthesia after the horse is standing or immediately?

Answer 20

Myopathy/neuropathy

Question 21

What causes myopathy/neuropathy after anesthesia?

Answer 21

Poor perfusion of muslces

Question 22

What is the treatment/prevention for myopathy/neuropathy?

Answer 22

Maintain MAP >70 mmHg
Appropriate padding
Adequate positioning on surgery table