11 April 2009

Increased Intracranial Pressure

Although its name sounds as though it may occur from studying for a pathophysiology exam, increased Intracranial Pressure (ICP) actually is associated with impaired cerebral venous drainage and reabsorption of cerebrospinal fluid (CSF) (1).

The potential complication can come from a variety of pathologies including central nervous system edema, tumor masses, hematoma, hydrocephalus, venous obstruction and increased CSF volume (1p557-8).

Increased ICP can occur in four stages:

  • Stage 1 is a phase of potential danger from one of the complications listed previously.
  • Stage 2 is a gradual rise in ICP effectively causing cerebral perfusion to drop and a decrease in oxygenation that stimulates vasoconstriction to increase cardiac output, resulting in lowered consciousness of the patient.
  • Stage 3 is the established condition of rapid rise of ICP at a point where it is called the stage of decompensation and autoregulation is lost, resulting in increased blood volume in the brain, hypoxia and cytotoxic edema, which only makes things worse anc causing coma to deepen (1p558). A pattern of apnea for 15-60 seconds followed by deep, labored breathing that eventually becomes shallow and apneic again is called Cheyne-Stokes respiration (1p558). Carbon dioxide accumulation induces the cycled breathing (1p558). Hypoxia and vasoconstriction stretches pressure receptors in carotid arteries signaling the medulla to induce bradycardia (1p558).
  • Stage 4 results when cerebral perfusion pressure falls below 30 mm Hg, widespread necrosis begins, and compression of brain stem respiratory centers leads to respiratory arrest and death.

Reference List
1. Nowak TJ, Handford AG. Pathophysiology: Concepts and Applications for Health Professionals. New York: McGraw-Hill, 2004.

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