A 62-year-old male was admitted with diffuse subarachnoid hemorrhage, intraventicular extension of the hemorrhage, and early signs of hydrocephalus. An EVD was placed without complication. The EVD has functioned well and following placement the patient’s examination improved. The figure that follows is the waveform produced.
What occurs during the P3 peak?a. P3 represents the arterial pulse
Correct Answer: D
An external ventricular drain is a soft catheter than can be placed within the ventricular system of the brain for management of elevated intracranial pressure and both communicating and noncommunicating hydrocephalus by means of allowing for diversion of cerebrospinal fluid and potentially clearing the obstructive fluid like blood and pus. The above wave is a normal waveform that is produced during a normal cardiac cycle. The first peak found in the wave is P1 or percussion wave; it correlates with the arterial pulse transmitted through the choroid plexus into the CSF. The second peak is P2, or tidal wave, which represents cerebral compliance as it correlates with arterial pulse bouncing off the brain parenchyma. The third peak is P3, or dicrotic wave; it correlates with the closure of the aortic valve. In normal ICP, P1 > P2 > P3. If P2 > P1, it is indicated that ICP is likely elevated and the intracranial compliance is likely decreased. The respiratory ICP waveform correlates with the respiratory cycle.