Nervous system: Raised intracranial pressure Flashcards
What is normal ICP?
5-15mmHg
How can ICP be measured?
Do a lumbar puncture and measure the pressure using a manometer - see how far the CSF goes up the tube.
How is ICP usually regulated?
Autoregulation: vasoconstriction and vasodilation to maintain normal pressures whilst still perfusing adequately. Chemo-regulation: pH dependent (eg taken opiates CO2 rises), detected by chemoreceptors and there is vasodilation.
Blood, brain and CSF can all compensate to a degree, eg some CSF and venous blood is drained.
How does reduction in blood supply to the brain cause brain injury?
Less blood = less oxygen supplied to the tissues which is needed by mitochondria to make ATP. Without ATP the Na/K ATPase cannot function leading to a build up of Na in the cell and water follows. The cell becomes oedematous and will undergo apoptosis.
What are the signs are symptoms of raised ICP?
A generalised headache worse on wakening due to hypoventilation during sleep. Gets worse on straining and coughing (raises pressure in the thorax and abdomen which compresses major veins so there is a transient rise in venous pressure in the head). Worse on lying down (pressure in head is higher due to gravity).
Vomiting - compresses vomiting centre
Depression of consciousness - due to compression of the reticular formation.
In infants there can be slowly increasing head size and developmental delay.
Visual disturbances - CSF surrounds the optic nerve, papilloedema, retinal haemorrhages, lateral rectus palsy due its long IC course - compressed between pons and petrous part of the temporal bone.
What is cushings reflex?
A last effort to perfuse the brain, only happens at terminal stages of raised ICP and indicates foramen magnum herniation is imminent.
Triad:
- high BP due to SNS
- bradycardia SNS causes tachy but detected by baroreceptors
- low RR due to ischaemia of the resp centres
What are some causes of raised ICP?
- Increased blood volume: venous outflow obstruction, venous sinus thrombosis
- Cerebral oedema: inflammatory response eg meningitis, encephalitis, infarction, diffuse head injury (most common cause of RICP by far)
- Increased CSF: impaired absorption eg hydrocephalus, IC hypertension, excessive secretion eg choroid plexus papilloma
- SOLs: abscess, tumour, haematoma
What is hydrocephalus?
Accumulation of CSF due to an imbalance of production and absorption causing enlargement of the ventricles.
Occurs in 1 in 1000 births
Non-communicating: CSF obstructed within the ventricles or between the ventricles and the subarachnoid space. Most commonly due to aqueduct blockage.
Communicating: there is flow of CSF, caused by increased production or blockage of the venous system.
What would you suspect the causes of RICP to be in a child?
Hydrocephalus
Tumours - brain tumours are the 2nd most common childhood cancers after leukaemia. Most commonly astrocytomas or medulloblastomas.
What are the most common brain tumours in adults?
Gliomas, meningiomas
Metastases from lung, breast and kidneys
How is raised ICP managed?
Dependent on the cause:
- Increased blood volume: anticoagulation
- Cerebral oedema: treat the cause, mannitol, hypertonic saline
- Increased CSF: shunts, tumour resection, diuretics in the mean time eg furosemide, carbonic anhydrase inhibitors
- SOLs: craniotomy, steroids are high value for brain tumours
Who needs to be notified about a patient with acute raised ICP?
Neurosurgeons
Peri-arrest team
Anaesthetist - when GCS reaches 8 patient stops protecting their own airway so need intubation
Is lumbar puncture a first line investigation for raised ICP and why?
No - taking CSF from the central canal causes negative pressure which could increase the risk of brain herniation.
