Intracranial pressure (ICP) is the pressure within the cranial vault relative to the atmospheric pressure. Quincke first measured cerebrospinal fluid (CSF) pressure in 1891 via a lumbar puncture (Quincke, 1891). In 1902, Cushing demonstrated hypertension, bradycardia and respiratory changes in an animal model with severe ICP elevation (Cushing, 1902). In 1951, Guillaume and Janny first described the use of continuous ICP monitoring using an intraventricular catheter (Guillaume & Janny, 1951). Nine years later, Lundberg described ICP wave patterns and their response to medical and physiological interventions (Lundberg, 1960).
ICP measurement has been an invaluable tool in research and clinical practice. It has contributed much to the understanding of intracranial pathologies, and assessment of therapeutic interventions. Intracranial hypertension is the elevation of the intracranial pressure to levels that may lead to neurological injury. ICP monitoring is used for patients with neurological disorders that have a high risk of further neurological injury from increased ICP or mass effect. In this chapter, we discuss the physiology related to ICP, the techniques in measuring ICP, interpretation of ICP recordings, common ICP disorders and their management (including intracranial hypotension), and outcome studies of ICP monitoring and management of intracranial hypertension.
Intracranial physiology and intracranial Pressure
The pressure wave of the ICP is generated by the transmission of arterial pressure from the major cerebral arteries (Martins et al., 1972) and CSF production by choroid plexus (Cardoso et al., 1983) in the cranial vault. In normal conditions, the transmitted pressure is attenuated by displacement of CSF back and forth through the foramen magnum into the distensible spinal dural sac. This provides a compliance mechanism for the cranial vault (Martins et al., 1972). In adults, the range of normal resting ICP is 0 to 15mm Hg (0 to 20cm H2O). Sustained ICP greater than 15mm Hg is considered abnormal. The relation of ICP to brain injury depends on the cause, acuity, severity and duration of the ICP. Transient elevations of ICP occur with coughing, sneezing, or Valsalva manoeuvres and do not cause harm in most persons.