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Are the following true or false regarding head injury?

True / False

A Glasgow coma score of 13-14 two hours after injury, is an indication for a CT scan Correct

The cerebral perfusion pressure (CPP) should ideally be maintained between 60 and 70mmHg Correct

Cerebral autoregulation is usually well maintained after a severe head injury Correct

The use of an intraventricular catheter is the gold standard for measuring intracranial pressure Correct

A mild head injury is associated with a Glasgow coma score of 10-13 Correct

Explanation

Head injury is defined by NICE as any trauma to the head other than superficial injuries to the face. Mild head injury makes up around 90% of all cases (GCS 13-15), moderate 5% (GCS 9-12) and severe head injury 5% (GCS =8).

In patients with head injury the normal autoregulation of cerebral blood flow (CBF) is lost and CBF becomes proportional to cerebral perfusion pressure (CPP), which in turn is directly determined by both the mean arterial pressure (MAP) and the intracranial pressure (ICP):

CPP = MAP - ICP

Use fluids, and where necessary vasopressors, to achieve a MAP greater than 80-90 mmHg. This figure is recommended as a guide until ICP monitoring is established, and assumes that the ICP is 20 mmHg and therefore ensures a CPP of at least 60-70 mmHg. Once ICP monitoring is established then treatment is targeted at maintaining CPP 60-70 mmHg. A CPP < 50 should be avoided. Aiming for higher CPP targets (>70) has been associated with adverse cardiorespiratory outcomes.

An external ventricular drain (EVD) is perhaps the gold standard method of measuring ICP via an intraventricular catheter.

The following indications for performing a head scan in head-injured patients are provided by the National Institute for Clinical Excellence (NICE) in the UK:

GCS less than 13 at any point since injury

GCS equal to 13 or 14 at two hours after injury

Suspected open or depressed skull fracture

Any sign of basal skull fracture

Post-traumatic seizure

Focal neurological deficit

More than one episode of vomiting, and

Amnesia of events, for greater than 30 minutes before impact.

In normal individuals the ICP is 0-10 mmHg and this is largely determined by autoregulation of CBF (that is, the amount of blood in the cranium). Vasoconstriction or vasodilatation of cerebral vessels occurs in response to changes in MAP, PaO2, PaCO2 and blood viscosity.

Reference:

NICE. Head injury: assessment and early management (CG176).

The Association of Anaesthetists of Great Britain and Ireland. Management of Head Injuries.

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