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RAISED INTRACRANIAL PRESSURE
  1. Laurence T Dunn
  1. Correspondence to:
 Mr Laurence T Dunn, Department of Neurosurgery, Institute of Neurological Sciences, Southern General Hospital, Glasgow G51 4TF, UK;
 ltd1x{at}udcf.gla.ac.uk

https://doi.org/10.1136/jnnp.73.suppl_1.i23

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    Raised intracranial pressure (ICP) is a common problem in neurosurgical and neurological practice. It can arise as a consequence of intracranial mass lesions, disorders of cerebrospinal fluid (CSF) circulation, and more diffuse intracranial pathological processes. Its development may be acute or chronic. There are well established methods for the measurement, continuous monitoring, and treatment of raised ICP. Evidence from prospective randomised controlled clinical trials that monitoring and treatment of raised ICP per se improves outcome is currently lacking for many conditions.

    ▸ PATHOPHYSIOLOGY

    The normal range of ICP varies with age (table 1) though values in the paediatric population are not well established. Thresholds for initiating treatment for intracranial hypertension vary according to aetiology and within single conditions there is debate about the appropriate upper limit of normal. For example, various authors have suggested thresholds of 15, 20, and 25 mm Hg for the initiation of treatment for raised ICP in patients with head injury.

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    Table 1

    Normal intracranial pressure values

    Table 2 lists some common causes of raised ICP.

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    Table 2

    Examples of causes of raised intracranial pressure

    Volume–pressure relations

    The relation between volume and pressure within the cranium is non-linear (fig 1). The Monro-Kellie hypothesis states that the sum of the intracranial volumes of blood, brain, CSF, and other components (for example, tumour, haematoma) is constant. The skull is considered as an enclosed and inelastic container. An increase in the volume of any one of the intracranial contents must be offset by a decrease in one or more of the others or be associated with a rise in ICP. Intracranial blood (especially in the venous compartment) and CSF are the two components whose volume can adapt most easily to accommodate an increase in the volume of intracranial contents. Once these compensatory mechanisms are exhausted, further increases in volume result in large rises in ICP. Compliance (the …

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