INTRACRANIAL PRESSURE (ICP)
a. Changes Caused by Intracranial Pressure. A patient with head injury may
experience an alteration in his level of consciousness. Other symptoms associated with
a severe head injury may include convulsions, delirium, coma, paralysis, and increased
intracranial pressure, which will be discussed here. The skull (a container that cannot
expand) holds the brain, vascular tissue, and cerebrospinal fluid. Any problem (trauma,
edema, tumor, infection, or bleeding) which adds to the contents of the skull will result in
an increase in intracranial pressure in the skull. That increased pressure sets off the
changes listed below:
(1) As the intracranial pressure increases, the blood vessels are squeezed
from the outside, restricting blood flow throughout the arteries.
(2) As the brain notes a drop in blood pressure, the sympathetic defenses
respond, causing the blood pressure to increase.
(3) Respiratory changes occur due to the chemoreceptors that sense
changes in the blood chemistry.
The vagus nerve is affected, causing the pulse to slow.
(5) Cushing's response - Increased blood pressure characterized by slow
pulse. This is a clear but late sign of increased intracranial pressure.
(6) As the intracranial pressure progresses, the level of consciousness is
altered. Eventually, unconsciousness occurs because the body's vital functions cannot
operate properly. Ultimately, there is brain death due to loss of adequate cerebral
perfusion (passage of fluid through the brain).
(7) Once the brain's ability to compensate is exhausted, the areas of the
brain shift, causing herniation.
Compression may be from above (central syndrome) or from the side (lateral
syndrome). The central syndrome progresses in a more orderly manner and
causes unconsciousness early.
b. Progressive Levels of Intracranial Pressure. Three progressive
levels of intracranial pressure can be identified.
Progressive level one.
Involves cerebral cortex and upper brain stem.
(b) Blood pressure rises, pulse slows.