INTRACRANIAL PRESSURE (ICP) & IT'S MEASUREMENT

🔸The ICP waveform is a modified arterial pressure tracing

🔸 It has 3 peaks: P1, P2 & P3

🔸 P1 is a result of transmitted pressure from choroid plexus

🔸 The amplitude of P2 changes with brain compliance. If compliance is poor, amplitude will be high ( can even exceed that of P1) and vice versa

🔸P3 represents the dicrotic notch

🔸 Lundberg (A) or Plateau waves are steep rise of ICP to over 50 mm of Hg and lasting for 5-20 minutes; then it falls abruptly. Are always pathological and indicates significantly reduced compliance

🔸 Lundberg (B) waves are oscillations occurring every 1-2 minutes where ICP rises to over 20-30 mm of Hg from baseline in a crescendo manner. They are supposed to be result of altered cerebral (B)lood volume and altered tone of cerebral (B)lood vessels 

🔸 Lundberg (C) waves are oscillations whose amplitude is less than that of B waves and are supposed to result because of interactions between cardiac and respiratory (C)ycles. They occur also in healthy individuals 

METHODS OF MEASUREMENT OF ICP

 Intraventricular catheter - ventriculostomy represents the "gold standard" for pressure measurement

 

✔️Normally placed in the frontal horn of lateral ventricle 

✔️Allows therapeutic CSF drainage 

✔️Creates a pathway for infection 

✔️Potential for accidental venting of CSF

✔️Possible subdural haemorrhage or upward brain herniation 

✔️ Catheter obstruction & ventricular haemorrhage may occur 

 Subdural bolt 

✔️ "Richmond Screw" or "Leeds device" inserted through a burr hole & an opening in the dura & arachnoid remains intact

 

✔️connects via a fluid couple to a transducer 

✔️ less invasive 

✔️ may underestimate high ICP and damping is a problem

 Subdural catheter 

✔️ Usually subdural space over frontal lobe of non-dominant hemisphere is selected

✔️ Prone to signal damping and calibration drift 

✔️ Potential risk of infection 

✔️ Doesn't require penetration of brain tissue

 Intracerebral transducer 

✔️Inability to check zero calibration & drain CSF 

✔️ Risk of infection

✔️Less reliable

🔸The incidence of infection ~ 2-7% with monitoring ≥ 5 days

🔸The risks are slightly greater with dural penetration 

🔸The zero reference point of the transducer is usually taken as the external auditory meatus 

🔸 Rather than the waveform type, the important factors appear to be the degree and duration of ICP elevation