The Munroe-Kellie doctrine
states that the brain is part of a closed system encased in a solid mass of bone, the skull. The brain has 3 main components: brain tissue, CSF, and blood... all of which must coexist in the limited space available inside the skull.
high ICP
is defined as a pressure 15 mm Hg. This increased pressure may be due to an increase in any of the 3 above components. **
Death can occur if ICP is sustained at 30 mm Hg. for any period of time.
** We can, and do have quite high, but transient increases
How does the brain maintain homeostasis?
Brain tissue normally accounts for 80-85% (1400 ml) of the intracranial contents; cerebral blood, 3-10% (150 ml), and CSF 8-12% (150 ml.) In order to maintain homeostasis, what must occur? If (and this is an important statement), any increase occurs in th
How is regulation of cerebral perfusion maintained?
Metabolic regulation, Increased ICP, Decreased O2, Increased O2.
Cerebral Perfussion Pressure - (CPP)must be maintained at 70-80 mmHg to maintain adequate blood flow to the brain. Under 50 mmHg, neurological damage occurs.
When the ICP is increasing in pathological states, the following compensatory mechanisms take over
1. Blood is shunted away from the brain 2. CSF production decreases 3. CSF is shunted away from the brain via the arachnoid villi and veins
When the compensatory mechanisms fail to control ICP....
decompensation is said to occur. If the amount of space available within the skull is reduced for any reason, ICP will rise.
What does rising ICP eventually lead to, if left untreated?
decreased brain perfusion and possible brain herniation to brain stem
How does the brain respond to the buildup of C02 and developing acidosis?
Artery dilation ? increased blood flow (this allows more O2
& glucose to come to the brain). However, this also ? ICP.
--Upon development of a "vicious cycle" what happens if this cycle is not interrupted???
...
--What happens to cells that become hypoxic?
...
Causes of IICP include:
trauma
lesions of any type
inflammation of brain tissue
any time there is an CSF
acidosis (can occur with malnutrition)
The major complication of untreated IICP?
The major complication of untreated IICP is brain herniation
Nursing care:
Wholly Compensatory - assessment for ICP
most sensitive and earliest sign of deteriorating
neuro status: ? LOC
memory changes: Slowing of speech ? lethargy & finally coma N&V: Recurrent & projectile; often no warning of
nausea. D/t pressure on medulla.
Nursing goals to reduce IICP:
To promote venous drainage from the head (more space in cranial vault) To promote fluid balance in the brain with medication ( cerebral edema) To maintain respiratory patterns (increase O2 Vessel constric. & decrease blood vol.) To decrease metabolism de
Promoting Venous Drainage from the Head
1. Positioning - keep HOB at 35-40 degrees, keep patient's head in neutral position, no hip flexion. Remember the important principle: if BP up, put head up; if BP down, put head down. 2. Movement - move patient slowly, log roll - don't twist neck 3. Spac
Promoting fluid balance in the brain with medication
1. Osmotic diuretic - pulls H2O out of healthy brain cells which then enters the vascular system & excreted through the kidneys - Mannitol - 25-50% glucose. Given in bolus IV doses. Output should increase. 2. Vascular diuretics (tubular and loop) - help e
Maintaining respiratory patterns
1. Monitor respiratory patterns - may want to increase O2, suction 2. Ventilator care - may be ordered if ABG's abnormal. Increased O2 causes arterial constriction, hereby decreasing amount of blood in brain. This may cause brain ischemia & cell loss in p
Decreasing metabolism (decreasing O2 need)
1. May give Nembutal which produces barbiturate coma, decreasing metabolism. 2. Avoid stress which stimulates the SNS and ? ICP. Family staying with the pt. is often helpful 3. If hyperthermic, may use hypothermia blanket, Tylenol, or both. (Watch skin ca
Intracranial Monitoring (Assessment of ICP)
Purposes a) measuring ICP b) obtaining CSF samples c) withdrawing fluid to decrease pressure in the cranial
vault
Note: monitoring is used for acute brain conditions, such as head injuries, when ICP changes are rapid & unpredictable. It is not used for ch
Wave types or waveforms
a) A waves: an ominous sign of intracranial
decompensation. These waves measure 50-100 mm Hg, last 5-20 minutes minutes and denote cerebral ischemia and brain injury. A waves are treated with Mannitol and
Decadron. b) B waves: measured at 20-50 mm Hg, or
Monitoring devices:Epidural:
least invasive, carries lowest infection risk. How is this inserted? A tiny sensor is inserted into the epidural space through a burr hole.--Can CSF samples be withdrawn?
--Are measurements considered strictly accurate? Why or why not? --When is this type
Monitoring devices: Subarachnoid screw:
...
Monitoring devices: Ventricular catheter:
What is the best aspect of this device? CSF can be drained to ? ICP --What are 2 negative aspects? 1. infection risk 2. risk of brain damage (tissue damage or collapse of ventricle
Nursing Implications
extreme care in drawing off CSF, why?
How long may tubing be?
Not longer than 14 feet, or measurements may be
inaccurate. However, this may allow pt's. with S.A.
catheters to get OOB in chair.
How is tubing kept?
What is the greatest danger with these cat
Perfusion Pressure
N's. must also calculate the brain's perfusion pressure (MAP - ICP) on monitors. To be adequately perfused, the brain's perfusion pressure must be at least 70-80 mm Hg. Fluid & electrolyte balance are critical to perfusion
Avoidance of Injury
is of primary concern to the nurse with these
vulnerable patients.