ICP

Question 1

outline the MOnro Kelli hypothesis and describe what happens past the point of compensation

Answer 1

The Monro-Kellie hypothesis states that sum of the volumes of the brain (CSF, brain tissue and intracranial blood) is constant as it is in a fixed volume in the cranium. E.g. an increase in one causes a decrease in the other. The principal buffers are CSF, and to a lesser extent, blood volume (in the venous compartment especially). These can compensate for a short period of time, the point of decompensation is illustrated below (around 10 mmHg). Once these compensatory mechanisms are exhausted, further increases in volume result in large rises in ICP.

Question 2

what are the 4 most characteristic features of raised ICP

Answer 2

headache, vomiting and papilloedema

progressive deterioration in conscious level (GCS)

Question 3

why is raised ICP headache classically worse in morning/wake from sleep

Answer 3

• lying flat - rise in ICP
• resp depression whilst asleep - inc CO2
• dec CSF absorption?

Question 4

what will exacerbate an ICP headache

Answer 4

anything that further increases ICP eg coughing and sneezing

Question 5

when does vomiting tend to occur

Answer 5

in morning with headache

Question 6

when does papilloedema develop?

Answer 6

may take several days

Question 7

what can be seen int eh eye due to an acute and severe rise in ICP

Answer 7

fundal haemorrhage

Question 8

what is a cingulate herniation

Answer 8

brain tissue forced under falx cerebri

Question 9

what is an uncal herniation

Answer 9

uncus (medial part of temporal lobe) herniates inferior to the tentorium cerebelli

Question 10

what is the clinical syndrome assoicated with an uncal herniation

Answer 10

progressively imaired consciousness, dilated ipsilateral pupil (CNIII) and contralateral hemiplegia

Question 11

tonsillar herniation

Answer 11

cerebellar tonsils herniate down through teh foramen magnum

Question 12

outline the relation between CPP and ICP

Answer 12

CPP = MAP - ICP

Normally, cerebral blood flow is maintained at a constant level by cerebrovascular autoregulation. If this autoregulation is impaired, changes in MAP or ICP can have direct effects on cerebral blood flow.

Question 13

what physiological response can inc ICP have

Answer 13

reflex bradycardia - cushings triad

Question 14

outline cushings triad

Answer 14

• compresses the arteriole, this decreases cerebral blood flow to the point of cerebral iscahemia
• This activates the sympathetic response, which causes vasoconstriction of blood vessels (hypertension) and an increase in heart rate
• Baroreceptors in the aortic arch detect this and trigger a parasympathetic response via CNX, induces bradycardia. Cushing’s ulcers develop in the stomach due to increased production in stomach acid.
• Both HTN and raised ICP compress the respiratory centre at the brain stem causing irregular breathing