28.1 Interventional and Neurointerventional Radiology Anesthesia

Why This Topic Matters on the NCE

Domain IV.A.11 of the content outline is non-operating-room anesthesia (NORA) with five sub-topics, of which interventional radiology is one. Closed claims analyses consistently show that NORA claims involve a higher proportion of death and a higher proportion of inadequate oxygenation and ventilation than operating room claims, and that monitored anesthesia care is disproportionately represented. The environment, not the procedure, is the hazard.

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1. The ASA Requirements for Any Anesthetizing Location

The ASA Statement on Nonoperating Room Anesthetizing Locations sets a minimum that must be verified before every case:

1. A reliable oxygen source with a backup E-cylinder
2. Adequate and reliable suction
3. An adequate scavenging system where inhaled anesthetics are used
4. A self-inflating resuscitation bag capable of delivering at least 90 percent oxygen
5. Adequate anesthetic drugs, supplies, and equipment
6. Adequate monitoring equipment meeting the ASA standards for basic monitoring
7. Sufficient electrical outlets, including one isolated-power or ground-fault-protected circuit
8. Adequate illumination of the patient, machine, and monitors, plus a battery-powered backup light
9. Sufficient space for personnel and equipment, with unobstructed access to the patient and machine
10. An emergency cart with a defibrillator, emergency drugs, and resuscitation equipment
11. Adequately trained support staff and reliable two-way communication to request assistance
12. Compliance with all applicable building and safety codes and postanesthesia care standards

The practical version of this list is: you will be alone, in the dark, behind a lead screen, far from the patient, with no immediate help. Plan accordingly.

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2. Environment-Specific Hazards

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3. Neurointerventional Radiology

Mechanical thrombectomy for acute ischemic stroke

The highest-acuity NORA case, and the one where anesthetic management most directly affects neurologic outcome.

• General anesthesia versus conscious sedation was debated for years because observational data favored sedation. Three randomized trials — SIESTA, ANSTROKE, and GOLIATH — found that general anesthesia was not inferior, and GOLIATH even favored it, provided that hypotension was strictly avoided. The signal in the older observational data was blood pressure, not the technique itself.
• The blood pressure rule is the whole answer: avoid a fall in mean arterial pressure of more than about 10 to 20 percent from baseline, and avoid a systolic below roughly 140 mmHg before recanalization. The ischemic penumbra depends entirely on collateral flow, which is pressure dependent.
• Thrombolysis thresholds: blood pressure must be below 185/110 mmHg before intravenous thrombolytic administration and maintained below 180/105 mmHg for 24 hours afterward.
• Time is brain. Door-to-groin-puncture time is a quality metric; anesthetic induction must not delay the procedure.
• Avoid hyperglycemia and hyperthermia, both of which worsen infarct outcome. Maintain normocapnia.

Aneurysm coiling and other neurovascular work

Covered in detail in the intracranial vascular section. The essentials: general anesthesia with absolute immobility, systemic heparinization to an activated clotting time roughly 2 to 2.5 times baseline, protamine reversal immediately for perforation, and thrombolytic or glycoprotein IIb/IIIa therapy without reversal for thromboembolism.

Carotid artery stenting

Balloon dilation and stent deployment at the carotid bulb stimulate the carotid sinus baroreceptors, producing sudden profound bradycardia, hypotension, or asystole. Anticipate it: have glycopyrrolate or atropine drawn up before deployment, and have transcutaneous pacing available. Hyperperfusion syndrome after stenting requires strict blood pressure control.

Arteriovenous malformation and tumor embolization

Liquid embolic agents (Onyx, n-butyl cyanoacrylate) and particles are delivered through microcatheters. Absolute immobility is required. Provocative testing with amobarbital or lidocaine may be performed in an awake patient before embolization near eloquent territory.

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4. Body Interventional Radiology

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5. Contrast Media

Iodinated contrast reactions

These are anaphylactoid (non-IgE mediated) in the great majority of cases, which is why prior uneventful exposure does not guarantee safety and why prophylaxis works at all.

• Mild: urticaria, nausea, flushing
• Moderate: bronchospasm, significant urticaria, vasovagal reaction
• Severe: anaphylactoid shock, laryngeal edema, cardiac arrest — treated exactly as anaphylaxis, with epinephrine first

Premedication for a patient with a prior reaction is typically prednisone 50 mg orally at 13, 7, and 1 hour before the study plus diphenhydramine 50 mg one hour before, with a shorter intravenous hydrocortisone regimen for urgent cases. Note that "shellfish allergy" is not a specific predictor; the relevant history is a prior contrast reaction or severe atopy.

Contrast-induced nephropathy

• Risk factors: preexisting chronic kidney disease, diabetic nephropathy, hypovolemia, heart failure, large contrast volumes, and nephrotoxin co-administration.
• Prevention: intravenous isotonic hydration and minimizing contrast volume. N-acetylcysteine and sodium bicarbonate are not supported by the best evidence.
• Metformin does not cause nephropathy, but if acute kidney injury occurs, accumulated metformin can cause lactic acidosis. Current guidance is to hold metformin at the time of contrast administration and for 48 hours afterward in patients with reduced eGFR or receiving intra-arterial contrast, restarting only after renal function is confirmed stable.

Gadolinium

Used for MRI. In patients with severe chronic kidney disease, older linear gadolinium agents were associated with nephrogenic systemic fibrosis; newer macrocyclic agents carry markedly lower risk, but eGFR should still be checked.

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Exam Traps

• NORA claims involve more death and more inadequate oxygenation than operating room claims, and monitored anesthesia care is over-represented.
• In stroke thrombectomy, avoiding hypotension matters more than choosing general anesthesia or sedation.
• Carotid stent deployment causes bradycardia — have an anticholinergic ready.
• Contrast reactions are anaphylactoid, not IgE-mediated, and are treated with epinephrine when severe.
• Hold metformin for 48 hours after contrast in the at-risk patient because of lactic acidosis, not nephropathy.