1.2 ICP Flashcards
a) What are the symptoms (10%) and signs (20%) of raised intracranial pressure (ICP) in an adult?
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a) What are the symptoms (10%) and signs (20%) of raised intracranial pressure (ICP) in an adult?
Symptoms:
Headache: bursting, throbbing. Exacerbated by sneezing, exertion, recumbency.
Worse in morning after a period of recumbency, raised
PaCO2 associated with sleep, reduced CSF reabsorption.
> > Vomiting.
> > Visual disturbance.
a) What are the symptoms (10%) and signs (20%) of raised intracranial pressure (ICP) in an adult?
Signs:
> Respiratory irregularity,
Cheyne-Stokes breathing, neurogenic
hyperventilation due to tonsillar herniation.
> > Cushing’s triad: hypertension with high pulse pressure, bradycardia and
associated irregular respirations.
> > Eye signs: papilloedema,
fundal haemorrhages, pupillary dilatation,
ptosis, impaired upward gaze (midbrain compression), abducens palsy.
> > Progressive reduction in consciousness due to caudal displacement of midbrain.
b) Describe the physiological principles underlying the management of raised ICP. (40%)
Monroe Kelly doctrine underpins the physiology of ICP
States Skull is a fixed volume containing 3 constituents
Brain / CSF / Blood
an increase in one of the constituent parts neccesiateates a decrease in one of the otherwise a rise in ICP is inevitable.
CO2
An increase CO2 leads to vasodilation and a rise in ICP from increase blood volume
Tight control of CO2 and hyperventilation causes CO2 -> vasoconstiction
to fall and a reduction in ICP
Nurse 30’ head up
This facilitates venous drainage from brain and reduced blood volume and icp
Loose neck ties
same as above
Diuretics
Osmotic diuretics such as mannitol drag h2o from brain and lead to a reduction in brain volume and excretion of volume in urine
drops icp
b) Describe the physiological principles underlying the management of raised ICP. (40%)
The cranium is a closed compartment (Monroe–Kelly doctrine).
The sum of its contents (brain, CSF, blood, other) must therefore remain the same.
If the amount of one component increases, some compensation can occur by reducing the amount of one of the other components.
Once these compensatory mechanisms are exhausted, ICP will rise, ultimately causing pressure on the brain, herniation and thus direct tissue damage.
Physiological manipulation of the quantity of each of the components can limit ICP rise.
b) Describe the physiological principles underlying the management of raised ICP. (40%)
CSF
Blood
> > Reduce CSF: diuretics, mannitol, hypertonic saline, elevation of head of
bed 15–30 degrees, CSF drain.
> > Reduce blood:
• Optimise venous drainage: avoid tight tube ties, head-up tilt 15–30 degrees, paralyse to reduce valsalva, treat seizures with anticonvulsants, avoid excessive PEEP and peak airway pressures.
• Avoid excessive arterial flow: maintain PaO2, keep PaCO2 low-normal, anaesthetise to reduce cerebral metabolic rate of oxygen (CMRO2) and avoid pyrexia.
b) Describe the physiological principles underlying the management of raised ICP. (40%)
Brain
Other
> > Reduce brain: mannitol, avoid hyperglycaemia, avoid hypotonic fluid
administration.
> > Reduce other: evacuate clot, excise tumour.
Stop the cranium being a closed compartment: decompressive craniectomy.
b) Describe the physiological principles underlying the management of raised ICP. (40%)
One of the main issues of a rising ICP is the impact it has on cerebral perfusion pressure (CPP), according to the equation:
CPP = MAP − ICP (or JVP, whichever is higher)
Therefore, in the early stages of rising ICP (before direct pressure brain damage occurs),
the effects can be mitigated by maintaining CPP through manipulation of mean arterial pressure (MAP) and jugular venous pressure (JVP).
> > Maintain MAP: avoid dehydration and pyrexia, and use vasopressors to target a MAP of 80 mm Hg (this value depends on ICP, which may not be known).
> > Reduce JVP: as previously, optimise venous drainage.
c) What methods are used to manage or prevent acute rises in ICP? (30%)
A
B
Airway:
» Intubate.
Respiratory:
> > Aim PaO2 >13 kPa and
PaCO2 4.5–5 kPa, keep PEEP <15.
> > Hyperventilation to PaCO2 4–4.5 kPa
may be used for short time periods
in emergency situations with
refractory intracranial hypertension.
c) What methods are used to manage or prevent acute rises in ICP? (30%)
C
D
Cardiovascular:
» 15–30-degree head-up tilt,
tube ties not too tight/tape tube,
head in neutral position,
increase sedation and paralyse if coughing or straining,
ensure that MAP >80 (depends on ICP, if being monitored).
Neurological:
» Adequate sedation to reduce CMRO2,
treat seizures,
treat pyrexia,
monitor for and manage hyperglycaemia
(target 6–10 mmol/l).
c) What methods are used to manage or prevent acute rises in ICP? (30%)
Pharm
Pharmacological:
» Mannitol 0.25–1 g/kg.
> > Hypertonic saline 5% 2 ml/kg.
> > Consideration of CSF drain, under expert guidance.
> > Decompressive craniectomy in specialist centre.
