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
What are some extra measures that can be used in patients with raised ICP (other than osmotherpay, hyperventilation, and surgical evacuation)
Sedation, analgesia, paralysis (reduce cerebral O2 demand; prevent coughing and straining)
Nurse the patient head up 30 degrees
TXA (if due to traumatic head injury)
What should be the target MAP in head injured patients?
> 90mmHg
What is the best resuscitation fluid in head injured patients?
0.9% saline. Better than balanced crystalloids.
What is the best resuscitation fluid in head injured patients?
0.9% saline. Better than balanced crystalloids.
What should be the target intracranial pressure?
<20mmHg
What shoudl be the target cerebral perfusion pressure?
> 60mmHg
What anti-seizure medication should be given to prevent fits in head injured patients?
Prophylactic pheytoin.
What medication should be used to treat HTN in subarachnoid haemorhage?
Labetolol
What do fixed dilated pupils indicate in a seizure?
Fixed and dilated pupils are a feature of generalised convulsions.
They do not necessarily indicate herniation.
