Anesthetic Considerations for the Horse

Question 1

What is unique about the morbidity/mortality rate in horses?

Answer 1

Higher

Question 2

How do anesthetic depressants effect horses (CV)?

Answer 2

Very sensitive
Decreased myocardial contractility
Decreased CO, BP
Inotropic support is key

Question 3

Tissue perfusion in horses

Answer 3

Poor
Post-anesthetic myopathy

Question 4

How do anesthetic depressants effect horses (ventilation)?

Answer 4

Hypoventilation common - mechanically ventilate
Severe V/Q mismatch = physiologic shunt = low PaO2 = hypoxemia
Give high flow of O2 in recovery

Question 5

Horses are what type of breathers? What is the significance?

Answer 5

Obligate nasal-breathers
Risk of obstruction in surgery
Nasal congestion

Question 6

When should e-tubes be removed in horses?

Answer 6

Swallowing
Standing!!

Question 7

Is pre-op fasting recommended in horses?

Answer 7

Not supported

Question 8

What impact does anesthesia have on GI motility?

Answer 8

Decreases GI motility
Stress, drugs, transport, pain all increase risk of ileus

Question 9

What impact does prolonged recumbency have on horses?

Answer 9

High risk of myopathies and neuropathies
V/Q mismatch
Stand within 1 hour after anesthesia

Question 10

Horses must do what after anesthesia?

Answer 10

Horses MUST stand after anesthesia
Most dangerous (and frustrating) period - 1/3 of anesthetic-related deaths during recovery

Question 11

Recovery complications

Answer 11

Fractures and other injuries from attempts to stand
Upper airway obstruction

Question 12

What should be done during recovery?

Answer 12

Maintain airway patent with e-tube
Prevent hypoxemia (O2 insufflation)
Padded recovery stall
Additional sedation
Assist recovery if indicated

Question 13

Sedation Drugs: Horses

Answer 13

a2 agonists: xylazine, detomidine, romifidine, dexmedetomidine
Acepromazine (10-20min prior)
+/- opioid (butorphanol, morphine, hydromorphone)

Question 14

Induction Drugs: Horses

Answer 14

Ketamine + diazepam/midazolam or propofol

Question 15

Maintenance Drugs: Horses

Answer 15

Total intravenous anesthesia (TIVA): ketamine/xylazine, “triple-dip” (ket, guaf, xyl), CRI (ket, xyl)
Inhalant anesthesia (IA): iso, sevo, des

Question 16

Pros/Cons: Total Intravenous Anesthesia

Answer 16

Anesthesia machine not required
Generally good recoveries
Time limit ~1hr
Avoid accumulation of drugs, prolonged recoveries

Question 17

Pros/Cons: Inhalant Anesthesia

Answer 17

Better mm relaxation
Procedure >1hr duration
Requires anesthesia machine
Oxygen supplementation
Ventilation can be assisted

Question 18

PIVA

Answer 18

Balanced anesthetic technique, adjuncts to inhalant anesthetics
a2 agonists, ket, lidocaine
Analgesia, decreased anesthetic resuirements
May influence recovery

Question 19

What is recommended with monitoring TIVA?

Answer 19

Nasal oxygen insufflation

Question 20

What must be monitored for IA?

Answer 20

Arterial BP is a must! - MAP > 70mmHg, hypotension MUST be treated
ECG, pulse-ox

Question 21

Pain Management: Horses

Answer 21

NSAIDs
a2s
lidocaine
ketamine CRI
systemic opioids
blocks

Question 22

Pain Management: Alpha 2s

Answer 22

Excellent analgesia
Heavy sedation
CV depression
Limited long-term use
Adjunct to GA

Question 23

Pain Management: Lidocaine CRI

Answer 23

Anti-inflam GI effects
Mild analgesia
Improves GI motility
Decreased anesthetic requirement
Does not improve CO

Question 24

Pain Management: Ketamine CRI

Answer 24

NMDA antagonist (“wind-up” pain”)
Decreased anesthetic requirement
Improves CO
Prolonged infusions may affect recovery

Question 25

Pain Management: Systemic Opioids

Answer 25

Can cause excitation
Increased locomotor activity
Usually used with sedation
Decreased GI motility
Controversia

Question 26

Pain Management: Local Anesthetics

Answer 26

Distal extremities only
Can use opioids intra-articularly
Epidural long-lasting