TCRN – Trauma Certified Registered Nurse

The Monro-Kellie doctrine states that the skull is a fixed box containing brain tissue (about 80%), blood (about 10%), and cerebrospinal fluid (about 10%); an increase in one component must be offset by a decrease in another. Early compensation displaces CSF into the spinal canal and venous blood out of the skull. Once compensation is exhausted, compliance falls and small additions of volume produce steep rises in pressure.

Normal intracranial pressure (ICP) in adults is about 5–15 mmHg. Cerebral perfusion pressure (CPP) = MAP − ICP. BTF guidelines recommend treating ICP > 22 mmHg and maintaining CPP 60–70 mmHg; CPP above 70 with aggressive fluids and vasopressors increases the risk of ARDS and is avoided. For example, a MAP of 80 mmHg with an ICP of 25 mmHg yields a CPP of 55 mmHg, which requires intervention on both sides of the equation.

ICP monitoring is indicated in salvageable patients with severe TBI (GCS 3–8 after resuscitation) and an abnormal CT (hematomas, contusions, swelling, herniation, or compressed basal cisterns). With a normal CT, monitoring is considered when two or more of the following are present: age over 40, unilateral or bilateral motor posturing, or SBP < 90 mmHg.

An EVD transducer is leveled at the tragus of the ear (approximating the foramen of Monro) and re-leveled with every position change. Drainage is set to a prescribed height or pressure threshold; clamp the drain before moving or repositioning the patient to prevent over-drainage, which can cause subdural hemorrhage or upward herniation. Monitor hourly drainage volume, color, and clarity, and maintain a closed system to reduce infection.

The normal ICP waveform has three peaks. P1 (percussion wave) reflects arterial pulsation, P2 (tidal wave) reflects brain compliance, and P3 (dicrotic wave) follows aortic valve closure. When P2 exceeds P1, compliance is reduced and the brain is poorly able to accept additional volume. Sustained plateau (Lundberg A) waves indicate critically low compliance.

Management proceeds in tiers, escalating only when a lower tier fails. Before escalating, exclude a surgical lesion with repeat CT and correct reversible causes: hypoxia, hypercarbia, fever, agitation, pain, seizure, hyponatremia, and venous outflow obstruction from a tight cervical collar or endotracheal tube tie.

Mannitol (0.25–1 g/kg IV bolus) creates an osmotic gradient that draws water out of brain tissue and improves blood rheology. It is an osmotic diuretic: expect brisk diuresis, avoid it in hypotensive or hypovolemic patients, place a urinary catheter, and hold further doses when serum osmolality approaches 320 mOsm/kg or the osmolar gap widens. Administer through an in-line filter because crystals can form.

Hypertonic saline (for example 3% infusion or bolus, or 23.4% bolus through a central line) reduces ICP while expanding intravascular volume, which makes it preferred in the hypotensive or hypovolemic patient. Monitor serum sodium frequently; protocols commonly cap sodium at about 155–160 mEq/L. Watch for volume overload and hyperchloremic acidosis.

Hyperventilation lowers ICP within minutes by causing hypocapnic cerebral vasoconstriction, but it also reduces cerebral blood flow and can cause ischemia, especially in the first 24 hours when flow is already low. Prophylactic hyperventilation (PaCO2 ≤ 25 mmHg) is not recommended. Brief hyperventilation is used only as a bridge for signs of active herniation while definitive therapy (osmotherapy, surgery) is arranged.

High-dose barbiturates (pentobarbital) reduce cerebral metabolic demand and are reserved for ICP refractory to maximal medical and surgical therapy; they are not given prophylactically. Monitor for hypotension, myocardial depression, and immunosuppression, and titrate to EEG burst suppression. Decompressive craniectomy removes a bone flap to allow the brain to expand; the flap may be stored in the abdominal subcutaneous tissue or a bone bank, and a helmet protects the defect. Prophylactic hypothermia is not recommended by BTF; mild hypothermia is at most a rescue measure for refractory ICP, while fever must be treated aggressively.

Herniation is the displacement of brain tissue across a rigid dural fold or through the foramen magnum. Recognizing the pattern early guides emergent interventions: elevate the head of bed, give a hyperosmolar bolus, briefly hyperventilate as a bridge, and prepare for emergent CT and neurosurgery.

In uncal herniation, a Kernohan notch phenomenon occasionally produces weakness on the same side as the lesion because the opposite cerebral peduncle is compressed against the tentorium; the dilated pupil remains the more reliable localizing sign. Respiratory patterns progress from Cheyne-Stokes (diencephalon) to central neurogenic hyperventilation (midbrain), apneustic breathing (pons), and ataxic breathing (medulla) as herniation descends.