Types of ICP monitors

Most commonly use:

External Ventricular Drain (EVD)

• Inserted at the bedside
• Sits in the ventricle
• has the benefit of being able to treat hydrocephalus and drain fluid as a means to lower ICP

Intraparenchymal Monitor (Licox)

• Sits in the parenchyma
• Monitors pressures
• Added benefit of being able to monitor oxygen tension (like an SVO2 for the brain)

Indications for ICP monitor​

GCS 3-8 with an abnormal CT​

GCS 3-8 with normal CT and:​

• Age > 40​
• motor posturing
• SBP <90

Potential benefits

• Early detection of mass effect​
• Limit indiscriminate therapies to control high ICP which can be harmful​
• Reduce ICP via CSF drainage (EVD) and other interventions​
• Some monitors can measure brain oxygen tension​
• May improve outcome ​

Potential pitfalls

• Finicky waveforms and inaccurate measurements
• Misinterpretation of waveforms
• Over-reliance on numbers
• Only tells you the pressure and/or oxygen tension of the parenchyma where the monitor is sitting
• Infection

Leveling of the Monitor​

• leveled at the tragus (why the tragus?)
• The tragus correlates to the location of the foramen of Munro which is the middle of the brain

Waveforms (like a CVP for the brain)

• P1 is the percussive wave and represents transmission of the arterial pressure from the choroid plexus to the ventricle
• P2 is the tidal wave and reflects brain compliance (reflection of the arterial pulse wave bouncing off the spongy brain parenchyma).  This wave should be lower than the percussive wave
• P3 is the dicrotic notch and represents closure of the aortic valve

• As intracranial pressures climb, brain compliance worsens

• With the brain becoming less compliant, the parenchyma cannot absorb the impact of the arterial pulse and P2 Tidal Wave become higher than the P1 Percussive Wave 

• If you see this on the monitor, in the context of an ICP monitor that has been working well, a severe TBI, an elevated ICP and a patient who has either a worsening clinical exam or a patient who is deeply sedated due to his/her elevated ICP, it is aids in confirmation and indication to intervene

Most important issue is to assess pupillary size and reactivity.  If there is a "blown" pupil(s) you must initiate emergency management

• Have someone page your attending or fellow

• Have someone page neurosurgery STAT

• Have the RT's hyperventilate the patient - usually with bag mask ventilation (see Hyperventilation later in this section)

• Give 250cc 3% IV STAT

• Give 50g Mannitol IV STAT

• If an EVD is in situ as the nurse to lower and/or open the drain to drain 5-10ccs

• if the head is cocked  - straighten it (see Positioning later in this section)

• if a cervical collar is in situ - loosen it

• Give a bolus of 2mg IV midazolam, 50ug Fentanyl, and Rocuronium 50mg (if not on an infusion of NMB)

• Order a STAT CT head (can always be cancelled if the patient goes directly to the OR)

If the Pupils are not blown you can use a systematic approach (see below)

• Hyperventilation is an effective rescue strategy to buy time until a patient can have a CT or get to an OR

• The way it works is that the low CO2 levels cause vasoconstriction which leads to less blood volume in the brain

• Vasoconstriction of course  also diminishes cerebral perfusion

• With this in mind, It is NOT a maintenance strategy

• CO2 for all cause brain injuries should be maintained between 35 and 40

• Often the more awake patients with brain injuries will hyperventilate on their own.  There is little that can be done about that as the risk/benefit of deeply sedating an awake, less severely injured patient who we can assess clinically does not favor this approach

• Perfectly straight with head midline

• Head of bed elevated to 30 degrees

• If no cervical collar is on there should be no kinks in the neck (impairs venous drainage)

• If cervical collar is in situ, make sure the collar is not too tight