Increased ICP & Traumatic Brain Injury

The cranium is a rigid, nonexpandable structure holding exactly three things — brain tissue, cerebrospinal fluid, and blood — and the total volume inside it stays constant. That is the Monro–Kellie doctrine, and everything else on this page follows from it: if any occupant grows (a hematoma, swelling brain, trapped CSF), one of the others must shrink to make room, or the pressure rises.

At first, compensation works: CSF is displaced toward the spinal canal and venous blood is squeezed out, holding ICP in its normal supine-adult range of 7–15 mmHg. But the buffer is small. Once it is spent, even a tiny added volume sends ICP climbing steeply — values above 20–25 mmHg are pathological, and once compensatory mechanisms fail, rapid decompensation may occur.

Rising pressure is not evenly distributed. It builds pressure gradients across the rigid dural folds and skull openings, and brain tissue is pathologically displaced across them — herniation, the event every neuro check exists to catch before it happens.

The brain is perfused by a pressure gradient: cerebral perfusion pressure equals mean arterial pressure minus intracranial pressure. Rising ICP therefore starves the brain two ways at once — it compresses tissue directly, and it subtracts from the pressure pushing blood in. In severe TBI the Brain Trauma Foundation sets the numbers: treat ICP above 22 mmHg (values above it are associated with increased mortality) and hold CPP between 60 and 70 mmHg for survival and favorable outcomes.

The equation hands the team exactly two levers: lower ICP (osmotherapy, CSF drainage, positioning) or support MAP (fluids, vasopressors). It also explains why hypotension and hypoxia are the preventable killers after brain injury — each episode deepens secondary injury, so keep SpO₂ > 90%, PaO₂ > 60 mmHg, and SBP above the BTF age-banded floors (≥ 100 mmHg at ages 50–69; ≥ 110 mmHg in younger or older patients). And remember: isolated head trauma usually does not cause hypotension — a hypotensive head-injured patient is bleeding somewhere else until proven otherwise.

CO₂ is the third, hidden variable: hypercarbia dilates cerebral vessels, adding blood volume to the closed box and raising ICP. So the target is normocapnia (ETCO₂ 35–45 mmHg), with brief hyperventilation to PaCO₂ ~30–35 mmHg reserved as a temporizing measure during acute herniation — prophylactic hyperventilation should be avoided, particularly in the first 24 hours after injury.

A traumatic brain injury is damage from an external mechanical force — closed (a blow or jolt) or penetrating. The primary injury is done at impact: fractures, contusions, hematomas. Nothing at the bedside can undo it. The secondary injury — the cascade of hypoxia, hypotension, elevated ICP, glutamate excitotoxicity, oxidative stress, and neuroinflammation that unfolds over the following hours to days — is the part nursing care exists to prevent. Severity is graded by GCS: mild 13–15 · moderate 9–12 · severe 3–8, with mild accounting for over 90% of cases.

Rising ICP declares itself in a predictable order, and the order is the exam question. The earliest sign is a change in level of consciousness — restlessness, agitation, confusion, increased drowsiness — because the cortex is exquisitely pressure-sensitive. Headache, vomiting, and blurred vision travel with it. Vital signs change late. By the time Cushing’s triad appears — hypertension with a widened pulse pressure, bradycardia, and irregular respirations — brainstem herniation is imminent. A nurse waiting for vital signs to confirm a gut feeling about a confused patient is waiting for the alarm that means it is nearly too late.

The triad has a mechanism worth knowing: the sympathetic system surges to force blood across the elevated ICP (restoring CPP) → baroreceptors answer the hypertension with reflex bradycardia → brainstem compression breaks the respiratory rhythm into shallow breaths with periods of apnea, sliding toward agonal respiration and arrest.

Epidural hematoma is an arterial story: a temporal bone fracture tears a branch of the middle meningeal artery, and blood collects between the skull and the outer dura — on CT a biconvex (lentiform) mass that rarely crosses suture lines. The classic course is the lucid interval: knocked out at impact, then a transient complete recovery, then rapid neurologic collapse as the arterial bleed expands. It occurs in only ~14–21% of cases and is not pathognomonic — but it is why a head-injured patient who “seems fine” still needs serial neuro checks. EDH is a neurosurgical emergency: outcomes deteriorate significantly when decompression comes more than 2 hours after the first neurologic decline.

Subdural hematoma is the venous mirror image: torn bridging veins ooze between the dura and arachnoid — a crescent-shaped collection that crosses suture lines. It stalks the elderly (cerebral atrophy stretches the bridging veins, so minor trauma suffices), chronic alcohol users, and anticoagulated patients. Timing defines it: acute < 72 h, subacute 3–21 days, chronic > 3 weeks — and chronic SDH presents insidiously as gait decline, cognitive slowing, and confusion, a classic missed diagnosis mistaken for stroke or dementia.

Basilar skull fracture breaks the floor of the cranial vault and announces itself in sequence: hemotympanum within hours, then raccoon eyes (periorbital ecchymosis) and Battle’s sign (mastoid ecchymosis) delayed 1–3 days, with possible CSF rhinorrhea or otorrhea — a torn dura leaking spinal fluid, an open door to meningitis. It carries one absolute nursing rule: no nasogastric tubes or nasotracheal intubation — a blind tube can pass through the fractured skull base into the cranium, with catastrophic consequences.