NUR245 Lecture Week Four Day 1 Intracranial Regulation (ICP).

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NUR245 Lecture Week Four Day 1 –
Intracranial Regulation (ICP)
*** straightforward disease process questions; S/S early/late, how to treat
someone – it’s about application more than definitions ***

REMEMBER:
STEMI, NSTEMI: troponin elevated
Unstable angina: no troponin elevation Chapter

56 (red book), 61 (purple book)


Intracranial Regulation:
3 components in the brain:
1. CSF (10%)
2. Intravascular blood (12%)
3. Brain tissue (78%)
 does not store oxygen + glucose

Causes of IICP:
ANY INJURY TO THE BRAIN will cause the tissue to expand
- tumor
- bleed (stroke)
- injury, swelling

Factors Influencing IICP:
- arterial pressure (ART, BP)
- central venous pressure
- intraabdominal, intrathoracic pressure
 why? Causes back pressure on the jugular veins  decreases CSF + blood
drainage, leading to IICP
 ex: putting someone on the ventilator, PEEP (+ ventilating someone puts
pressure on jugular veins, which decreases drainage of CSF and blood)
- *** posture ***
 HOB should be > 30 degrees/semi-Fowler’s; never take care of an IICP
patient supine!
- maintain normal body temperature

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 febrile = metabolism increases, which increases blood flow to the brain 
increases ICP
- ABG = manipulating CO2 (CO2 is a vasodilator; low CO2 increases
vasoconstriction; IICP? Treat by lowering CO2)

*** Monro-Kellie Doctrine ***
- only applies to closed brain; once it’s open (craniotomy), this doctrine
doesn’t apply
 understand this! It won’t be asked straightforward; we need to understand
it in order to apply it towards a patient condition
*** “if the volume of one component increases, another must decrease to
maintain ICP” ***
EXAMPLE OF APPLICATION: elevated BP? CSF will seep out somewhere to
accommodate the increase of blood
“brain injury, clear fluid coming out of nostril – check for glucose in the
clear fluid”  application of this doctrine
 brain can’t handle everything, so something has to trickle out; there’s
simply not enough room for everything
 craniotomy = piece of skull removed to allow for swelling; skull inserted in
thigh or placed on ice while we let ICP come back down

*** >20 = emergency IICP ***
Normal: 5-15 mm Hg




Normal Compensatory Adaptations:

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Change in CSF = brain will displace the CSF into subarachnoid space OR it
will spill into nasal passage
Increase in intracranial blood volume = cerebral vasoconstriction or dilation
+ changes in venous outflow
Changes in brain tissue/volume = brain tissue will compress or distend The
brain can’t compensate for all of these changes, leading to IICP Volume
increase continues leads to decompensation  compression  ischemia

Cerebral Blood Flow:
- “amount of blood (mLs) passing through 100 g/brain in 1 minute”
*** maintaining blood flow is critical; we must maintain adequate amount of
oxygen and glucose for the brain ***
 ischemic brain cannot be replaced; any deficit lost cannot be regained
Autoregulation:
- automatic adjustment in diameter of cerebral blood vessels; ensures
consistent cerebral blood flow
 *** only effective if MAP >65 ***

Cerebral Perfusion Pressure (CPP):
Definition: pressure needed to ensure adequate blood flow to the brain
- normal: 60-100 mm Hg
- < 50  ischemia, nerve death
- < 30  incompatible with life
*** maintain MAP to maintain perfusion to brain *** 
CPP measured by transcranial doppler (U/S)

Cerebral Blood Flow, Condensed:
CPP = MAP - ICP

Definitions Made Easy:
ICP elevation reduces cerebral perfusion pressure/CPP
- high ICP results in low blood pressure to brain (NOT good) -
brain autoregulates all of this for us 

Factors Affecting CBF:
*** application-style questions; KNOW THESE ***
- increased PaCO2
 relaxes smooth muscle, dilates cerebral vessels, decreases vascular
resistance, increases CBF
- decreased PaCO2