Neurology

Front 1

Which parts of the PNS arise from the NEURAL TUBE ?

Back 1

skeletal motor neurons
axons of preganglionic autonomic neurons

Front 2

Which parts of the PNS arise from the NEURAL CREST CELLS ?

Back 2

sensory neurons
postganglionic autonomic neurons

Front 3

Reducing ICP

Back 3

To decrease ICP, you need to decrease the volume occupied by the contents inside the skull. These contents are:
1. the space occupying lesion / intracranial bleed
2. arterial blood volume
3. venous blood volume
4. brain volume
5. CSF volume

We will leave #1 - although it is obvious that in a case like a large extradural, access to a neurosurgeon is very urgent, to remove the blood that is pressing on the brain!!

2. decrease (intra-cranial) arterial blood volume
(Note that this is not the same as lowering the blood pressure! What this refers to is the VOLUME of blood in the arteries inside the head. When ICP is high, it may actually be necessary to increase the BP using noradrenaline etc to maintain CPP)
a) ventilate to achieve low-normal CO2 (because CO2 is a cerebral vasodilator)
b) we dont hyperventilate any more as this causes cerebral vasocinstriction, and worsens ischaemia
c) correct hypoxia
d) correct acidosis
e) prevent surges in arterial pressure (if these are too high, this may overcome the brain's ability to autoregulate flow, so a big rise in pressure results in a big surge in flow) by:
- ensure adequate sedation / anaesthesia
- analgesia
- intubation is very stimulating - RSI for a head injured patient is quite complex and requires blunting the sympathetic response to intubation, while also preventing a fall in BP
f) decrease cerebral metabolic rate
- hypothermia (but not shown to change outcome)
- adequate depth of anaesthesia/sedation
- produce "burst suppression" on the EEG using thiopentone (this is a last resort)

3. decrease (intra-cranial) venous blood volume (i.e. facilitate cerebral venous drainage)
a) elevate head of bed (as indicated)
b) head in neutral alignment
c) no ETT ties around neck (use adhesive tape instead)
d) loosen cervical collar (or use sand bags)
e) paralyse pt to prevent coughing / straining on the ETT
f) minimal or no PEEP
g) modify ventilation strategy to keep peak inspiratory pressures low

4. decrease brain volume
a) mannitol
b) hypertonic saline
c) frusemide
d) maintain serum Na+ around 145-150
e) minimise free water input (i.e. no 4%DN/5 etc)

5. drecrease CSF volume
a) insert external ventricular drain
b) acetazolamide (decreases CSF production)