Neurological Emergencies Flashcards
What is primary and secondary brain injury?
Primary: injury directly due to the insult.
Secondary: injury resulting from decreased O2 delivery.
What is the main mechanism of secondary brain injury?
Decreased O2 delivery to the brain.
Hyperglycaemia.
Electrolyte disturbances.
How do you calculate cerebral perfusion pressure?
CPP = MAP - ICP
Cerebral perfusion pressure is the difference between mean arterial pressure and intracranial pressure.
What are the two reasons why intracranial pressure is important?
- It is a major determinant of cerebral perfusion pressure.
- Raised ICP can result in herniation of the brain.
How do you reduce the volume of an oedematous brain?
Administer an osmotic diuretic (e.g. mannitol)
What is the mechanism of action of mannitol?
Mannitol is an osmotic diuretic, and therefore reduces brain oedema.
How do you reduce the volume of CSF?
Intraventricular drainage
How do you reduce the volume of intracranial circulating blood?
Hyperventilation - causes cerebral vasoconstriction.
What is the mechanism of action of hyperventilating a brain injured patient?
Hyperventilation causes cerebral vasoconstriction, which reduces intracerebral blood volume.
How rapid are the effects of mannitol?
Mannitol results in reduction of intracranial pressure within minutes.
Maximal effect is usually within 30 minutes or so.
Adverse effects of mannitol:
Can result in hypovolaemia (due to diuresis). Therefore only give mannitol if hypovolaemia has been corrected.
Renal failure.
What is hypertonic saline? What is its use in head injury?
Alternative to mannitol.
Useful in hypovolaemic patients as it increases circulating volume.
What are the pros and cons of hyperventilation?
Pro: reduces intracranial pressure
Con: reduces cerebral blood flow and perfusion
Therefore: only use hyperventilation if patient is showing signs of herniation, or if surgical evacuation has been unsuccessful.
What are the signs of herniation?
Hypertension
Bradyarrhythmias
Loss of brainstem reflexes (e.g. pupil reflexes)
Respiratory arrest
Dilated pupils
Target PaCO2 in hyperventilation
4 - 4.5 kPa