ICP Flashcards
(21 cards)
Volume components
Brain: 1400ml
CSF: 150ml
Blood: 150ml
(75-80% of BV is venous blood and 20-25% is arterial)
Compliance
Change in volume observed for a given change in pressure.
C = 🔺V / 🔺P
Elastance
The change in pressure observed for a given change in volume
E = 🔺P / 🔺V
Ohm’s Law Equation
Q = 🔺P / R
Q = flow
🔺P = proportional gradient between flow and outflow
R = resistance to flow
Ohm’s Law Equation
Q = 🔺P / R
Q = flow
🔺P = proportional gradient between flow and outflow
R = resistance to flow
Ohm’s Law Definition
Describes the relationship of the difference between systolic and diastolic pressures divided by the resistance (viscosity and vascular resistance)
Viscosity
Varies with hematocrit. An increased hematocrit increases viscosity and decrease flow. A decreased hematocrit decreases viscosity and increases flow.
CPP Formula
MAP - ICP = CPP
Normal CPP
Adults: 80mmHg
TBI: 60-70mmHg
CPP: 40-50mmHg
Auto regulation
Vasomotor (myogenic and adrenergic)
• as pressure increases vasoconstriction occurs, increasing CVR and maintaining a constant CBF.
• as pressure decreases vessels dilate and CVR Decreases again maintaining a constant CBF.
PaCo2 affect
Hypercarbia - vasodilation
Hypocarbia - vasoconstriction
Acidosis - vasodilation
Alkalosis - vasoconstriction
Normal ICP in supine position
0-15 mmHg
Intracranial HTN is ICP greater than what?
20 mmHg lasting more than 5 minutes or more
ICP devices can be placed in what locations?
Epidural, subdural, subarachnoid space, parenchyma, and intraventricular compartments.
When is ICP appropriate to monitor?
With a severe head injury, GCS 3-8 after resuscitation, and abnormal head CT (hematoma, contusion, edema, compressed basal cisterns)
What if it’s a severe head injury with a normal CT?
Criteria: age >40 years, SBP < 90mmHg, unilateral or bilateral motor posturing.
What are subjective signs and symptoms of elevated ICP?
• altered LOC (confusion and lethargy)
• visual disturbances
• headache
• nausea and vomiting
• seizures
• restlessness or agitation
What are some Objective signs and symptoms of elevated ICP?
• CN palsies (lll, VI, X)
• visual dysfunction
• papilledema
• pupillary changes
• spontaneous periorbital bruising
• motor dysfunction
• ataxia
• changes in vital signs
What are some early changes in elevated ICP? (Objective)
• hypertension and tachycardia (Cushing reflex) caused by stimulation of SNS at level of hypothalamus
• abnormal respiratory pattern (cheyne-stokes)
• nystagmus
What are late signs of elevated ICP? (Objective) Cushing Triad (medulla)
• hypertension with widened pulse pressure (vasomotor center)
• bradycardia (cardiac center)
• abnormal respiratory pattern (ataxic or agonal)
What does ICP waveform reflect? (What causes the waveform)
The interaction of the arterial input, intracranial contents, and venous outflow.
• originates from arterial pulsation with retrograde venous pulsation.
