Intracranial Pressure - Merkin

Question 1

What are the two types of brain edema and what is the difference?

Answer 1

Vasogenic: disruption in the integrity of the blood vessel wall (tight junctions are separated)

Cytotoxic: failure of pumps, Na+ enters the surrounding cells and draws fluid out of blood vessels

Question 2

What are the types of herniation?

Answer 2

Cingulate (under the falx cerebri)
Uncal (tentorial-under tentorium cerebelli)
Tonsillar (brain stem)
External (through broken skull)

Question 3

What are the neurological effects of uncal/tentorial herniation?

Answer 3

Contralateral hemiparesis (before decussation of corticospinal tracts)

Ipsilateral oculomotor nerve palsy (with midriasis)

Atypical herniation:
Pushes whole brainstem to contralateral side so all symptoms are contralateral

Question 4

What are the effects of tonsilar herniation?

Answer 4

Top to bottom compression of the brainstem.

Cushing’s triad:

1. hypertension (progressively increasing systolic blood pressure)
2. bradycardia
3. irregular respirations (Cheyne-Stokes respiration, curves of fast, deep breathing with breaks of apnea)

Question 5

Formula for cerebral blood flow

Answer 5

CBF = (A-V)/R = CPP/R

A – mean arterial (inflow) pressure
V – mean venous (outflow) pressure
ICP – intracranial pressure (basically the same as venous pressure because of compression)
CBF – cerebral blood flow
CPP – cerebral perfusion pressure

Question 6

How is Cerebral Perfusion Pressure (CPP) related to intracranial pressure (ICP) and how do they compensate for each other?

Answer 6

CPP = A - ICP

When ICP is normal and arterial pressure decreases, CPP decreases
When ICP increases and arterial pressure is normal, CPP decreases

Arterial pressure increases to compensate for increased ICP to keep CPP normal, this is why hypertension is part of Cushing’s triad.

Question 7

How does brain compliance compensate for increased intracranial pressure with increased volume?

Answer 7

In a theoretical rubber balloon, intracranial pressure increases linearly with volume.

In biological herniation, at first no increase in pressure because the brain squeezes out CSF, then venous blood (arterial blood only squeezes out if ICP exceeds arterial pressure and there won’t be flow in this case).

When most of the CSF and venous blood has been squeezed out, brain begins to squeeze out and the ICP increases- low compliance.

At some point the brain compliance decompensates and the ICP shoots up.

In elderly, shrunken brain means higher compliance. P-V curve moves to the right.

Question 8

How are patients monitored for increased ICP?

Answer 8

If they are conscious it means they have sufficient perfusion pressure.

Otherwise measure ICP:

Gold standard: Intraventricular catheter
Intraparenchymal most popular

Keep CPP > 70 mm Hg (because under 50 can be irreversible) by keeping ICP < 20-25 mm Hg (vessels won’t necessarily reopen if ICP spikes and lowers)

Monitor over time: If ICP undulates (“A” plateau) this is a bad sign even if ICP doesn’t appear high, means low compliance

Question 9

What are the treatments for increased ICP?

Answer 9

1. elevated head (about 30’, if also spinal injury then antiTrandelenburg position)
2. hyperventilation (PCO2=29-31 mmHg)-shrinks the volume and thus decreases ICP, causes vasoconstriction but need to be careful to not increase resistance and decrease CBF)
3. sedation (decrease metabolism, blood flow and volume)
4. mannitol (0.5-1.0 g/kg IV)-increases osmolarity in blood to diurese (monitor so don’t decrease renal perfusion)
5. CSF withdrawal - not lumbar puncture because compartmentalization can cause herniation, but if it can be removed from ventricles will decrease ICP. (Skull fracture here is better than not)
6. steroids (effective in tumors not trauma)
7. surgery (last resort-for lifesaving in bad prognosis)