🧠 Increased Intracranial Pressure
The skull cannot expand. Why a change in consciousness comes first, why Cushing’s triad comes last, and the positioning that actually lowers pressure.
🧬 Why pressure rises at all
The Monro–Kellie doctrine: the skull is a closed box holding three things — brain tissue, blood and CSF. Their total volume is fixed.
If one increases, another must decrease, or the pressure rises.
| Contents of the skull | Roughly | What increases it |
|---|---|---|
| Brain tissue | 80% | Tumor, abscess, cerebral edema |
| Blood | 10% | Hemorrhage, vasodilation from high CO&sub2; |
| CSF | 10% | Hydrocephalus, blocked drainage |
Normal ICP is 5–15 mmHg. Sustained pressure above 20 needs treatment.
CPP = MAP − ICP Cerebral perfusion pressure is what actually reaches the brain. Keep it above 60 mmHg — as ICP climbs, perfusion falls, which is what kills tissue.
Compensation works until it suddenly does not. A patient can look stable and then deteriorate within minutes once the reserve is used up.
👀 Recognizing it — in the right order
Signs appear in a sequence, and the exam tests whether you know which comes first.
🚨 Cushing’s triad — three changes, all late
| Sign | Direction |
|---|---|
| Blood pressure | Systolic rises, diastolic stays → widening pulse pressure |
| Heart rate | Falls — bradycardia |
| Respirations | Irregular — Cheyne–Stokes |
Cushing's triad is never the answer to "earliest sign". It is the body's last-ditch attempt to force blood into a compressed brain.
👶 In an infant it looks different
The fontanelles and open sutures let the skull expand, so the early picture is a bulging fontanelle, a high-pitched cry, separated sutures, poor feeding and irritability — not headache and vomiting.
📈 Glasgow Coma Scale
Eye opening 1–4 · Verbal 1–5 · Motor 1–6. Maximum 15, minimum 3.
GCS of 8 or less means the airway is not protected. "Less than 8, intubate"
🩺 What lowers the pressure
Every intervention does one of three things: improve venous drainage out of the head, reduce the volume inside, or stop anything that spikes the pressure further.
🛍️ Positioning — free, and it works
| Do | Why |
|---|---|
| Head of bed 30° | Promotes venous drainage by gravity |
| Head midline, neutral | A turned or flexed neck kinks the jugular veins |
| Avoid hip flexion | Raises intra-abdominal and intrathoracic pressure |
| No Trendelenburg | Head-down position raises ICP directly |
🚨 Things that spike ICP — cluster care to avoid them
- Suctioning — limit to 10 seconds, hyperoxygenate first
- Coughing, sneezing, straining — give stool softeners, avoid the Valsalva maneuver
- Hip flexion, neck flexion
- Clustering painful care together — space activities out and allow rest between
- Noise and bright light — keep the room quiet and dim
| Drug | What it does | Watch |
|---|---|---|
| Mannitol (osmotic diuretic) | Pulls fluid out of brain tissue | Rising urine output means it is working; watch osmolality and electrolytes |
| Hypertonic saline (3%) | Same osmotic effect | Sodium levels |
| Dexamethasone | Reduces edema around tumors | Glucose; not used in head trauma |
| Antiepileptics | Seizures spike ICP sharply | Levels |
| Sedation / analgesia | Lowers metabolic demand and agitation | Must still be able to assess LOC |
⭐ The CO&sub2; lever
CO&sub2; is a potent cerebral vasodilator. Letting it rise dilates cerebral vessels, adds blood volume and raises ICP.
So oxygenation and ventilation are neuroprotective. Brief controlled hyperventilation may be used as a rescue — but prolonged hyperventilation causes ischemia by over-constricting the vessels.
⚠️ What goes wrong
🚨 Herniation
Brain tissue is forced through an opening it does not belong in. Signs of impending herniation:
- Unilateral fixed dilated pupil — “blown pupil”, usually on the same side as the lesion
- Rapid drop in GCS
- Posturing, then flaccidity
- Cushing’s triad
A newly blown pupil is a neurosurgical emergency. Report immediately - do not wait for the next scheduled assessment.
Decorticate posturing
Arms flexed in toward the core. Damage above the brainstem.
CORE = flexion toward the core
Decerebrate posturing
Arms extended and rigid, palms out. Brainstem damage.
Worse than decorticate. Moving from decorticate to decerebrate = deterioration.
🧠 Diabetes insipidus after brain injury
Pressure on the pituitary can stop ADH release — liters of dilute urine, rising sodium, falling blood pressure. Common after frontal craniotomy. Watch hourly urine output and sodium.
🎯 NCLEX traps
- Earliest sign = change in LOC. Not pupils, not the triad
- Cushing’s triad is late — and the pulse pressure widens
- HOB 30°, head midline — never flat, never Trendelenburg
- Suction ≤10 seconds, hyperoxygenate first
- GCS ≤8 → intubate
- Rising urine output on mannitol is expected, not a complication