Ratio > 1.0 is hallmark of impending intracranial decompensation.
Morphology Analysis
Analyze the CSF pulse pressure waveform by comparing P2 and P1 peaks to assess intracranial compliance and reserve status.
Guidelines & Evidence
Clinical Details
Section 1
When to Use
When to Use
Interpreting ICP pulse waveform morphology during continuous monitoring via an intraparenchymal (Codman/Camino) or intraventricular (EVD) transducer.
Suspected obstructive hydrocephalus or shunt malfunction in the outpatient setting during infusion studies.
Section 2
Literature
Development
The three-peak ICP waveform model — P1 (percussion), P2 (tidal), P3 (dicrotic) — was described by Lundberg and later Cardoso & Galbraith in the 1970s-80s. The fundamental insight is that intracranial compliance can be directly inferred from the _shape_ of the waveform. As the brain loses its buffer capacity (e.g. shunt obstruction), the relatively tall and compliant P2 rises disproportionately and overtakes P1.
Section 3
Pearls/Pitfalls
Absolute ICP vs Waveform
A patient can have a "normal" mean ICP of 15 mmHg while already having a P2/P1 ratio of 1.3 — indicating that their compliance reserve is nearly gone. They are one minor Valsalva or positional change away from a dangerous Lundberg A-wave (plateau wave). The waveform is a leading indicator; the mean ICP is a lagging indicator.
Section 4
Evidence Appraisal
Primary Reference
Analysis of the cerebrospinal fluid pulse wave in intracranial pressure
Cardoso ER et al. • J Neurosurg. 1983;59(5):817-21
