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Cardiac·CA-2

Critical Aortic Stenosis: Hip Repair

85 y.o. with symptomatic AS for urgent hip surgery. Balance the risk of spinal hypotension vs. general anesthesia.

The stem

An 85 y.o. female with a history of syncope and severe aortic stenosis (Valve Area 0.6 cm², Mean Gradient 50 mmHg) presents with a femoral neck fracture after a fall. She is in significant pain. The surgeon wants to proceed with a hemiarthroplasty today. PHYS: BP 110/70, HR 62 (Sinus), O2 Sat 94%.

Focus

Hemodynamic goals for AS (Slow, Sinus, SVR), and the debate between spinal vs. general anesthesia.

Examination relevance

AS is a 'fixed output' lesion. Defending your choice to avoid a single-shot spinal is a core test of cardiovascular physiology knowledge.

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Expert sample response

This patient has critical, symptomatic aortic stenosis and is at extreme risk for cardiovascular collapse. My primary goal is maintaining the 'Aortic Squeeze'—keeping the SVR high to ensure coronary perfusion to the hypertrophied LV.

I will avoid a single-shot spinal, as the rapid and unpredictable sympathectomy can lead to a drop in SVR that would be lethal in this fixed-output state. Instead, I will perform a General Anesthetic with a slow, titrated induction using etomidate and low-dose opioids, maintaining a phenylephrine infusion to strictly defend the MAP. I will also have an arterial line placed pre-induction for beat-to-beat monitoring. My hemodynamic targets are a heart rate of 60-80 and a MAP at or slightly above her baseline. If she develops AFib, I will immediately cardiovert, as the loss of the atrial kick will cause an immediate 40% drop in her cardiac output.

Full walkthrough

What the Examiner Is Testing

This case tests the hemodynamic mnemonic for aortic stenosis — slow, sinus, high SVR — and specifically whether you understand why a single-shot spinal is dangerous. The examiner wants to see you articulate that AS is a fixed-output lesion and that a sudden drop in SVR cannot be compensated.

The Board Trap

The trap is doing a spinal because "that's what we do for hip fractures in the elderly." A single-shot spinal drops SVR rapidly and unpredictably over 5 to 10 minutes. In a patient with AS and EF dependent on high afterload for adequate coronary perfusion, that SVR drop can cause severe coronary ischemia and cardiovascular collapse. You cannot fix it fast enough.

Walk-Through: How This Case Plays Out

Examiner: The orthopedic surgeon says she needs surgery today. Do you proceed?

Me: I would proceed — a hip fracture left untreated in an 85-year-old increases mortality rapidly. The question isn't whether to operate, it's how. I want an arterial line placed before induction for beat-to-beat monitoring. I'd start a phenylephrine infusion before I give any anesthetic agents to maintain SVR. This patient cannot tolerate any drop in her MAP.

Examiner: The family asks why you won't do a spinal. Can you explain?

Me: I would explain that a spinal would drop her blood pressure rapidly and unpredictably, and her heart cannot compensate because the aortic valve is so tight that it limits how much blood can flow out per beat. The heart muscle is very thick from working against the valve for years, and it needs high pressure to perfuse its own blood supply. If we drop her BP too quickly with a spinal, we risk a heart attack on the table. A general anesthetic with careful titration gives me control that a single-shot spinal doesn't.

Examiner: Thirty minutes into the case, she goes into atrial fibrillation with a ventricular rate of 140. BP drops to 75/40. What do you do?

Me: I would cardiovert immediately — synchronized DC cardioversion at 200 joules. In severe AS, atrial fibrillation causes an immediate 40% drop in cardiac output because this patient is completely dependent on the atrial kick to fill a stiff, hypertrophied ventricle. There's no time to rate-control and wait. I'd confirm the synchronization button is on to avoid precipitating VF, and I'd have the defibrillator charged before I push any rate-control agent.

Examiner: Post-op, her BP is running at 90/50. Is that acceptable?

Me: No. Her pre-op baseline was 110/70 — 90/50 represents a significant drop from her normals. I'd push phenylephrine to restore the SVR and call for urgent cardiac assessment if she doesn't respond. I'd check for new EKG changes suggesting ischemia. In severe AS, running below baseline MAP is a sign that the coronary supply is falling behind — I won't accept that as the new normal.

Key Phrases That Score Points

  • "Arterial line before induction — I need beat-to-beat monitoring in a patient with critical AS."
  • "Phenylephrine infusion running before I give any anesthetic agent."
  • "Single-shot spinal is contraindicated — rapid unpredictable SVR drop in a fixed-output lesion."
  • "New AFib in AS: cardiovert immediately, don't rate-control. Loss of atrial kick drops output 40%."
  • "Slow, sinus rhythm, high SVR — those are my three targets for the whole case."

Why This Case Appears on the Boards

Critical AS appears in nearly every board cycle because it tests pure cardiovascular physiology applied to a surgical decision. Defending the choice to avoid spinal anesthesia — and explaining the fixed-output physiology behind that choice — is a core marker of cardiovascular competency.