Anesthesia Protocols

Colic (Horse)

15 year old F Quarter Horse

Plan is exploratory laparotomy

Pertinent PE: Mildly obtunded, toxic MM, CRT 3s, HR = ꜛ54 (28-40) , rectal distended small intestine

Pertinent Hx: Colicky for 2 days, no change in weather or diet, treated unsuccessfully via medical management

Pertinent Clinpath: Lactate = mild ꜛ3.1(0.5-1.78 mmol/L), CK = ꜛꜛꜛ4540(60-330), Creat = 2.1 (0.4-2.2), abdominocentesis unremarkable

Pertinent U/S: Small intestinal gas distension

For each case:

1) ASA Status: Class IV

2) List anticipated complications based on procedure and protocol and assign a proposed reason for that complication

a. Tachycardia

b. Hypoventilation: Due to the use of an inhalant anesthetic

c. Hypotension: Due to the use of an inhalant anesthetic

d. Hyperthermia: Due to the use of an inhalant anesthetic, the procedure may be long, and it is not uncommon for adult horses to have a low temperature while under anesthesia.

e. Pain: This is a concern because this is an exploratory surgery and we don't know exactly what we will be dealing with.

f. Hemorrhage: This is a concern because this is an exploratory surgery and we don't know exactly where the necessary incisions will have to be made or what kind of damage is already done.

3) Premedication:

1. Xylazine: It's required to use an alpha2 agonist in horses, but Xylazine is the best choice because it causes biphasic vasodilation, whereas others cause persistent vasoconstriction. Vasoconstriction could cause problems since this horse's heart rate is already abnormally high.

2. Hydromorphone: Since butorphanol is expensive, short acting, and is only a mild to moderate analgesic, it wouldn't be a good choice for this patient. Hydromorphone is cheaper, lasts 2-4 hours, and 8 times more potent then morphine. Also, it doesn't cause any significant histamine release.

Induction:

1. Ketamine + Diazepam: Ketamine is commonly used in horses because it requires a much smaller dose compared to drugs such as propofol; and it is relatively cheap. Ketamine can cause muscle ridgity, thus diazepam, a muscle relaxant, is given with ketamine.

Maintenance:

1. Isoflurane: An inhalant anesthetic is used because the length of this surgery is unknown; therefore, TIVA would not be a good choice. Isoflurance is relatively cheap and quickly induces the patient.

4) Monitoring Devices:

1. Arterial Catheter connected to a Transducer: This direct measurement of blood pressure is commonly used in large animal on inhalant anesthetics. The consequences of hypotension are severe, so it is important to use the gold standard for measuring blood pressure.

5) Contraindicated Drugs:

1. Meperidine and Morphine: These opioids can cause histamine release, which can cause vasodilation, tachycardia, and hypotension.

2. Buprenorphine and Butorphanol: These opioids are not strong enough analgesics for this patient.

3. Acepromazine: This sedative