External Ventricular Drains (EVDs) & ICP waveform interpretation

An EVD is a temporary closed sterile system that both invasively measures ICP and removes excess CSF. It is typically used when ICP is increased (e.g., hemorrhage, severe head trauma, large strokes, obstructing tumors). In addition to drainage of excess CSF, ICP guided medical & surgical interventions may reduce morbiditv & mortality.

ICP WAVEFORM INTERPRETATION:

Examining the ICP waveform and trends can provide useful information about CNS perfusion & compliance.

SHORT-TERM PATTERNS (seconds)

 • P1 - related to arterial pulse; to CPP

 • P2 - rebound of pulse; inversely to cerebral compliance (e.g. ↑P2 with ↓compliance)

 • P3 — related to dicrotic notch in arterial pulse

 • Normal - Trimodal pattern with P1 > P2, P3 is seen normally. Increased P1 may be seen with increased SBP

 • Increased ICP - A trimodal pattern with P2 > P1, P3 suggests abnormal CNS compliance usually due to increased ICP

 • Markedly Increased ICP - Loss of discreet waves is seen with markedly abnormal CNS compliance

LONGER TERM PATTERNS (minutes)

Periodic fluctuations in ICP over time fall into three discreet patterns, called Lundberg waves.

 • LUNDBERG A WAVES - Plateaus up to 50mmHg lasting 5-20 minutes; suggestive of impending brain hemiation

 • LUNDBERG B WAVES - Rhythmic Spikes in ICP every 30-120 seconds suggestive of cerebral

vasospasm

 • LUNDBERG C WAVES - low amplitude oscillations in ICP every 7-15 seconds that represent normal CNS homeostasis



- Dr. Nick Mark MD @nickmmark



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