Rising ICP and a Falling EVD Output After Aneurysmal SAH
Mr. R, 54, had an aneurysmal subarachnoid hemorrhage (WFNS grade 2) coiled 72 hours ago. He has an external ventricular drain leveled at 15 cmH2O above the tragus, draining 10–12 mL/hr, and a target CPP of 70–80 mmHg. At 03:00 his ICP is 24 mmHg sustained over 10 minutes, MAP 92 mmHg, EVD output 3 mL over the past hour, GCS 13 (E3 V4 M6) down from 14 (E3 V5 M6), with a new left arm drift. Pupils are 3 mm and brisk, temp 37.9°C, Na 136. He receives nimodipine and levetiracetam; no new sedatives have been given.
1. Calculate CPP and interpret it in context. What does the combination of falling EVD output, rising ICP, and new focal deficit suggest?
Read the worked answer
CPP = MAP − ICP = 92 − 24 = 68 mmHg, below the stated 70–80 target and below the common 70 mmHg threshold. The absolute value matters less than the trend: ICP rose while EVD output fell from 10–12 to 3 mL/hr, and the GCS dropped a point with a new focal drift.
That triad points first to CSF drainage failure (obstruction, kink, incorrect leveling, or catheter malfunction) with secondary intracranial hypertension, rather than a primary brain event. Vasospasm can cause a new focal deficit on day 3, but it does not usually raise ICP or reduce EVD output unless infarction with edema has occurred. Rebleed or seizure would more often cause abrupt deterioration, pupil change, or abnormal movements.
2. List your first four actions in priority order and give the rationale for each.
Read the worked answer
- Verify the EVD system - level at the tragus, check for kinks, closed stopcocks, clot, and air; confirm the drain is at the ordered height. If ordered, drain a small volume (e.g., 5–10 mL) to lower ICP, then reclamp. Never flush forcefully.
- Optimize ICP non-invasively - HOB 30°, head midline, loose collar, normocapnia (PaCO2 35–40), avoid hypoxia. Brief hyperventilation only for signs of herniation.
- Escalate and reassess - neuro checks and pupils every 15 minutes, notify the provider/rapid response, prepare for CT head and CTA.
- Protect CPP - maintain MAP with fluids/pressors per order while lowering ICP; check for seizure activity, fever, hyponatremia, and sedation effects. Prepare for EVD revision or osmotic therapy if ordered.
3. How would you distinguish vasospasm from EVD obstruction/hydrocephalus at the bedside, and what confirms each?
Read the worked answer
EVD obstruction/hydrocephalus: high ICP with low or absent CSF output, no pulsation in the tubing, improvement after leveling or draining per protocol, and CT showing enlarged ventricles. The focal deficit may be nonlocalizing or related to raised ICP.
Vasospasm: new focal deficit with normal or only mildly elevated ICP, no hydrocephalus, and usually days 3–14 after SAH (peak 7–10). Confirm with TCD (elevated MCA velocities, Lindegaard ratio >3) and CTA/DSA showing arterial narrowing; treat with nimodipine, euvolemia, induced hypertension per protocol, and endovascular therapy if refractory.
Seizure: EEG correlate, eye deviation, subtle twitching. Rebleed: sudden severe headache, pupil dilation, fresh blood on CT. The bedside exam narrows the differential; imaging and EEG confirm it.