21.1 Aneurysmal Subarachnoid Hemorrhage (03.E.1)

Aneurysmal subarachnoid hemorrhage (aSAH) is the classic thunderclap catastrophe of the neuro ICU: a saccular aneurysm ruptures into the basal cisterns, intracranial pressure spikes, and the patient either dies before arrival or enters a two-week window of rebleeding, hydrocephalus, and delayed ischemia. This topic is heavily tested because the decisions are time-stamped and easy to mix up with older dogma. Independent OpenExamPrep material for ABIM Neurocritical Care candidates should treat aSAH as a sequence: confirm blood, grade the patient, find and secure the aneurysm, start nimodipine, keep the patient euvolemic, drain symptomatic hydrocephalus, then hunt for delayed cerebral ischemia (DCI) from day 4 through day 14.

The 2023 American Heart Association/American Stroke Association (AHA/ASA) guideline (Hoh BL et al., Stroke 2023;54:e314–e370) replaced the 2012 document. It does not invent a new disease, but it does retire several habits still lingering on boards: routine antifibrinolytics, prophylactic hypervolemia, routine statins, and intravenous magnesium as DCI prophylaxis. Cite the guideline as a source of recommendations. This is independent OpenExamPrep teaching, not an official AHA or ABIM product.

Why the first 24 hours decide survival

Rebleeding is the early killer. Risk is highest in the first 24 hours after the sentinel bleed. The 2023 guideline states that surgical or endovascular treatment of the ruptured aneurysm should be performed as early as feasible, preferably within 24 hours of onset, with the goal of complete obliteration whenever that is technically possible. Partial coiling of the rupture site is a temporizing option only when complete obliteration cannot be achieved acutely in a salvageable patient.

Until the aneurysm is secured, avoid wild blood-pressure swings. AHA/ASA 2023 does not lock a single systolic target as a Class 1 number. Supportive text recommends gradual reduction when patients are severely hypertensive (systolic values in the 180–200 mm Hg range), strict avoidance of hypotension (mean arterial pressure below 65 mm Hg), and short-acting intravenous agents so you can reverse overshoot. Observational series still associate rebleeding with systolic pressure above 160 mm Hg, which is why many ICUs continue to use an unsecured-aneurysm systolic ceiling near 160 mm Hg while watching the neurologic exam. After the aneurysm is secured, that ceiling comes off so you can raise pressure if DCI appears.

Routine antifibrinolytic therapy (tranexamic acid or aminocaproic acid) is not useful for improving functional outcome (Class 3: No Benefit, Level A in the 2023 document). Reverse anticoagulants immediately. Nicardipine or labetalol infusions are typical pre-secure antihypertensives; avoid long-acting agents that will trap you when vasospasm later demands hypertension.

Clinical grading: Hunt-Hess and WFNS

AHA/ASA 2023 recommends a clinical scale at presentation to describe severity and frame prognosis. Two scales dominate test questions. Hunt-Hess is a bedside clinical grade. World Federation of Neurosurgical Societies (WFNS) grade is built from the Glasgow Coma Scale (GCS) plus the presence or absence of a motor deficit. High-grade aSAH (Hunt-Hess 4–5 or WFNS 4–5) does not automatically mean comfort care: aneurysm treatment is still reasonable after a frank discussion of likely outcome, including in older adults.

A patient who is GCS 14 with a hemiparesis is WFNS III, not II. A patient who is GCS 15 with an isolated third-nerve palsy from a posterior communicating artery aneurysm is still Hunt-Hess 2 and WFNS I. Those distinctions show up as one-best-answer traps.

Modified Fisher: blood burden and vasospasm risk

Clinical grade predicts death and disability. Modified Fisher (mFS) grade predicts radiographic vasospasm and, imperfectly, DCI. Thick cisternal clot and intraventricular hemorrhage (IVH) raise risk. The scale used at the bedside (Frontera and colleagues, building on Claassen) is:

Thick is generally clot filling a cistern or fissure (historically >1 mm). Thin is a film that does not fill the cistern. Original Fisher grade 4 (ICH or IVH without thick cisternal blood) was paradoxically lower-risk than Fisher 3; modified Fisher fixes that by giving thick blood plus IVH its own high-risk bin. Do not confuse mFS with Hunt-Hess: a wide-awake patient can still be mFS 4 and needs aggressive DCI surveillance.

Securing the aneurysm: ISAT and anatomy

The International Subarachnoid Aneurysm Trial (ISAT, Lancet 2002) randomized 2,143 patients whose ruptured aneurysms were judged suitable for both coiling and clipping. Death or dependence at 1 year was 23.7% after coiling versus 30.6% after clipping (absolute risk reduction about 7 percentage points). The ISAT population was mostly good-grade, small, anterior-circulation aneurysms. That is the evidence AHA/ASA 2023 uses when it gives Class 1, Level A preference to primary coiling for good-grade anterior-circulation aneurysms equally suitable for both treatments.

Other 2023 modality rules worth memorizing:

• Posterior-circulation aneurysms amenable to coiling: coiling in preference to clipping (Class 1).
• Large intraparenchymal hematoma with a depressed exam in a salvageable patient: emergency clot evacuation (Class 1).
• Age under 40 years: clipping might be considered for durability (Class 2b).
• Age over 70 years: superiority of coiling versus clipping is not well established (Class 2b).
• Specialists with both endovascular and open expertise should choose the modality from patient and aneurysm features (wide neck, MCA bifurcation with branches, hematoma needing decompression, blister aneurysm).

The Barrow Ruptured Aneurysm Trial (BRAT) was not a true randomized ISAT replica; it showed an early coiling advantage that attenuated with long follow-up and more incomplete occlusions after coiling. Boards still want ISAT numbers plus the caveat: suitable anatomy. A wide-necked middle-cerebral-artery aneurysm with an associated temporal hematoma is not an ISAT aneurysm.

Nimodipine: the one drug every aSAH patient receives

Nimodipine is a dihydropyridine calcium-channel blocker. It does not reliably angiographically reverse large-vessel vasospasm. It does improve functional outcome, which is why it is given to all aSAH patients, not only those with documented spasm.

AHA/ASA 2023 Class 1, Level A: early initiation of enteral nimodipine is beneficial in preventing DCI and improving functional outcomes. Supportive text specifies continued enteral administration at 60 mg six times a day. That is 60 mg by mouth or feeding tube every 4 hours for 21 days, the British aneurysm nimodipine trial regimen, started as soon as the diagnosis is made (FDA labeling: within 96 hours of onset).

If systolic pressure collapses after a dose, do not simply abandon the drug. Split to 30 mg every 2 hours so the 24-hour exposure stays near 360 mg while the peak hypotensive hit is smaller. If hypotension persists and threatens perfusion, hold a dose, restore volume, and add a vasopressor rather than leaving the patient both dry and nimodipine-naive. Never inject the oral liquid or capsule contents intravenously — that error has caused cardiovascular collapse and death and carries a boxed warning.

Routine statins and intravenous magnesium are not recommended for DCI prevention in the 2023 guideline.

Volume, blood pressure, and delayed cerebral ischemia — not triple-H

DCI is a clinical syndrome: a new focal deficit or a drop in consciousness lasting more than an hour, not explained by hydrocephalus, rebleeding, seizure, fever, or metabolic derangement, typically between days 4 and 14 (peak around days 7–10). Angiographic vasospasm is common; not all spasm causes DCI, and DCI can occur with only distal or microcirculatory disease.

Classic triple-H therapy (hypertension, hypervolemia, hemodilution) is retired as a prophylactic bundle:

AHA/ASA 2023: maintaining euvolemia can be beneficial (Class 2a). Elevating systolic pressure in symptomatic vasospasm may be reasonable (Class 2b). Prophylactic hemodynamic augmentation and hypervolemia should not be performed. For severe spasm with progressing deficits, intra-arterial vasodilators and balloon angioplasty may be reasonable (Class 2b).

Practical ICU translation: pick a euvolemic target (neutral daily fluid balance, clinical exam, maybe pulse-pressure variation or bedside ultrasound — not a standing order for 200 mL/h of albumin). When the patient develops a new arm drift on day 7, raise MAP with norepinephrine or phenylephrine after the aneurysm is secured, obtain CTA/CTP or catheter angiography, and call the endovascular team if deficits persist.

Hydrocephalus, EVD, and seizures

Acute hydrocephalus — enlarging ventricles, declining GCS, upward-gaze palsy, or a small fourth ventricle with a tight third — is treated with urgent CSF diversion. AHA/ASA 2023 Class 1: external ventricular drain (EVD) and/or lumbar drainage for acute symptomatic hydrocephalus. EVD is the default when the exam is poor, there is obstructive blood, or you need ICP data. Lumbar drainage requires communicating cisterns and a secured (or at least not actively rebleeding) aneurysm in most protocols; it is not the first move in a comatose patient with a casted fourth ventricle. Use an EVD insertion bundle to cut infection. Chronic symptomatic hydrocephalus later gets a shunt (Class 1).

New-onset seizures after aSAH: treat with an antiseizure medication for 7 days. Do not use routine prophylaxis in every patient; it can be considered in high-risk anatomy (ruptured MCA aneurysm, intraparenchymal hematoma, high clinical grade, hydrocephalus, cortical infarction). Avoid phenytoin because of excess morbidity in this population. Continuous EEG is useful when the exam is poor or fluctuating.

TCD and other DCI surveillance

AHA/ASA 2023: trained nursing detection of exam change is the core monitor. Transcranial Doppler (TCD), CTA, and CT perfusion, interpreted by people who do this work, can detect vasospasm and help predict DCI. Continuous EEG and invasive monitors may help in high-grade patients with no exam.

TCD numbers that still appear on exams (middle cerebral artery, adult):

TCD is a trend tool, not a diagnosis of DCI. Pair a velocity jump with the exam and, when needed, CTA/CTP.

Hyponatremia: cerebral salt wasting versus SIADH

Hyponatremia after aSAH is common and dangerous because it tracks with volume loss and DCI. Two mechanisms dominate, and the treatment is not the internist's default fluid restriction.

If you cannot tell them apart at 3 a.m., treat as CSW: replace volume and sodium. Fluid restriction in aSAH is a classic harm pathway.

Neurogenic stunned myocardium and neurogenic pulmonary edema

Catecholamine surge at rupture injures heart and lung. Neurogenic stunned myocardium (neurogenic stress cardiomyopathy) produces troponin rise, deep T-wave inversion or QT prolongation, and wall-motion abnormalities that often cross a single coronary territory or resemble apical ballooning. Coronary occlusion is the alternative, so ECG plus echocardiography (and catheterization when the story is ambiguous) still matter — but do not delay aneurysm treatment for an expected-to-recover neurogenic cardiomyopathy in an otherwise typical aSAH patient. The ventricle usually improves over days to weeks.

Neurogenic pulmonary edema (NPE) is acute, protein-rich alveolar flooding from sympathetic pulmonary vasoconstriction and capillary leak. It can look like aspiration or cardiogenic edema. Treat the airway, use lung-protective ventilation if intubated, and treat the brain (secure the aneurysm, control ICP). Distinguishing NPE from volume overload matters because the aSAH patient still needs euvolemia, not days of furosemide-driven hypovolemia.

Venous thromboembolism prophylaxis is part of the ICU bundle once the aneurysm is secured. Standard ventilator bundles apply. Glucose targets follow ordinary critical-care practice (avoid both hypoglycemia and uncontrolled hyperglycemia).

A worked ICU timeline

A 52-year-old with a thunderclap headache is Hunt-Hess 2, WFNS I. CT shows thick cisternal blood and IVH (modified Fisher 4). CTA shows a 6-mm anterior communicating artery aneurysm suitable for coiling. SBP is 188 mm Hg. You start a nicardipine infusion, give nimodipine 60 mg enterally, reverse nothing because the patient is not anticoagulated, and take the patient for coiling within hours. An EVD is placed for a declining GCS from hydrocephalus. Day 7: new right-arm drift, TCD MCA mean velocity 190 cm/s, Lindegaard ratio 4.8. The aneurysm is secured, so you raise MAP, keep the patient euvolemic, and obtain CTA. That sequence — early securement, nimodipine, EVD, then induced hypertension for DCI rather than prophylactic triple-H — is the chapter in one patient.