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ICP Waveform Interpretation — FRCA Final MCQ

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HardNeuroanaesthesiaICP Waveform InterpretationFRCA Final

A 62-year-old man with severe traumatic brain injury has a ventricular intracranial pressure monitor. The catheter is clamped for measurement, and the monitoring system is correctly levelled and zeroed. The waveform is reproducible and synchronous with the arterial pulse. Although the mean ICP is 16 mmHg, the P2 amplitude consistently exceeds the P1 amplitude. Which intracranial pressure-volume state is most strongly indicated?

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Correct answer: D — Reduced compensatory reserve

The correct answer is D. P1 is the percussion wave produced predominantly by transmitted arterial pulsation; P2 is the tidal wave and is influenced by intracranial compliance. With preserved compensatory reserve, the usual relationship is P1 > P2 > P3. As reserve is exhausted and the patient moves onto the steep portion of the intracranial pressure-volume curve, P2 rises relative to P1 and may exceed it. Thus, small additional intracranial volume increments may produce disproportionately large pressure increases, even before mean ICP becomes frankly elevated. CSF overdrainage more typically causes low or negative ICP and is not diagnosed by P2/P1 inversion. Brain death cannot be inferred from this morphology. Underdamping exaggerates waveform amplitude but does not specifically produce the reproducible physiological P2 predominance described after system checks.

Reference: Brasil S, et al. Intracranial Compliance Assessed by Intracranial Pressure Pulse Waveform. Brain Sciences. 2021;11(8):971. Figure 1 and abstract. https://pubmed.ncbi.nlm.nih.gov/34439590/