NAVLE Veterinary Anesthesia and Pain Management 5

Question 1

A 6-year-old intact male English Bulldog is scheduled for soft palate resection. During inhalant anesthesia with isoflurane, the patient develops a ventricular bigeminy rhythm. Which of the following inhalant agents, if used instead, would have posed the GREATEST risk for sensitizing the myocardium to catecholamine-induced arrhythmias in this patient?

Accepted Answer

Halothane

Answer

Halothane is well-documented to sensitize the myocardium to catecholamine-induced arrhythmias, a property far more pronounced than with modern agents like isoflurane, sevoflurane, or desflurane. This is particularly relevant in brachycephalic patients where hypoxia and hypercapnia can elevate endogenous catecholamines. Halothane's arrhythmogenic potential was a major reason it fell out of favor in veterinary and human anesthesia.

Question 2

You are administering a constant rate infusion (CRI) of medetomidine to a 10 kg dog at 1 mcg/kg/hr for intraoperative analgesia. The surgeon notes the surgical field has excessive hemorrhage and requests a vasopressor. Which vasopressor is CONTRAINDICATED in this patient due to risk of life-threatening hypertension when combined with medetomidine?

Accepted Answer

Epinephrine

Answer

Epinephrine combined with alpha-2 agonists like medetomidine or dexmedetomidine carries a significant risk of severe, potentially fatal hypertension. Alpha-2 agonists cause pronounced peripheral vasoconstriction (alpha-2B receptor mediated). Adding epinephrine's potent alpha-1 and alpha-2 agonist properties can cause an exaggerated hypertensive crisis. Vasopressin and norepinephrine carry lower risk in this context and are sometimes used cautiously, while phenylephrine's pure alpha-1 activity is more predictable, though still requires care.

Question 3

A 4-year-old spayed female cat with hypertrophic cardiomyopathy (HCM) requires anesthesia for a perineal urethrostomy. Which of the following induction protocols would be MOST appropriate to maintain cardiac output while avoiding tachycardia and excessive vasodilation?

Accepted Answer

Etomidate (1–2 mg/kg IV) + midazolam (0.2 mg/kg IV)

Answer

Etomidate is the preferred induction agent in patients with compromised cardiac function because it provides the most cardiovascular stability of any injectable induction agent — minimal effects on heart rate, contractility, and systemic vascular resistance. Midazolam reduces the myoclonus associated with etomidate. Propofol causes vasodilation and can cause hypotension. Ketamine increases heart rate and sympathetic tone, which is detrimental in HCM where diastolic filling is already impaired. Alfaxalone, while moderate, has more hemodynamic effects than etomidate in cats with significant cardiac disease.

Question 4

A horse undergoing a 3-hour exploratory celiotomy under general anesthesia (dorsal recumbency) develops post-anesthetic myopathy (PAM) in the triceps muscle group. Which of the following intraoperative factors contributes MOST directly to compartment syndrome-type PAM in the dependent muscles of an anesthetized horse?

Accepted Answer

Hypotension reducing perfusion pressure below compartment pressure

Answer

Post-anesthetic myopathy in horses is primarily caused by ischemia of dependent muscles due to the weight of the horse compressing muscle compartments. In dorsal recumbency, the triceps bears significant compressive pressure. When mean arterial pressure drops below the compartment pressure (commonly due to anesthetic-induced hypotension), perfusion pressure to the muscle is insufficient, causing ischemia, rhabdomyolysis, and potential compartment syndrome. Maintaining MAP ≥70 mmHg is a key intraoperative goal in equine anesthesia to prevent PAM.

Question 5

A 9-year-old dog with a meningioma is receiving mannitol (0.5 g/kg IV) preoperatively to reduce intracranial pressure (ICP). Which of the following anesthetic agents would be the MOST appropriate choice for induction to avoid exacerbating elevated ICP?

Accepted Answer

Propofol (4 mg/kg IV, titrated slowly)

Answer

Propofol reduces cerebral metabolic rate of oxygen consumption (CMRO2), cerebral blood flow, and ICP, making it the preferred induction agent in patients with elevated ICP. It should be titrated slowly to avoid hypotension, which would reduce cerebral perfusion pressure. Ketamine and tiletamine-zolazepam are contraindicated in patients with elevated ICP because they increase cerebral blood flow and ICP. Alfaxalone at a large bolus dose can cause cardiovascular depression and, unlike propofol, does not have the same well-established cerebroprotective profile in this context.

NAVLE - North American Veterinary Licensing Examination Practice Test

NAVLE - North American Veterinary Licensing Examination Practice Test

NAVLE Veterinary Anesthesia and Pain Management 5