Arterial Lines & Waveforms

Arterial lines permit continuous invasive blood pressure measurement, frequent arterial blood sampling, and analysis of the waveform can be used to estimate cardiac output, predict volume responsiveness, and identify specific pathologies.

SQUARE WAVE TEST

The arterial line can measure BP inaccurately unless properly calibrated. Rapidly flushing the line (by pulling the release on the flush device) generates a square wave. Counting oscillations after the square wave indicates if the arterial line is working properly

 • Normal = accurate BP

 • OVERdamped = falsely LOW BP

 • UNDERdamped = falsely HIGH BP

SPECIFIC ARTERIAL WAVEFORM PATTERNS

 • Pulsus alternans - alternating strong and weak pulses; seen in low cardiac output shock states

 • Pulsus bisfirens - double peaked pulse in severe AR ± AS

 • Pulsus tardus - late peaking pulse; seen in severe AS

PULSE PRESSURE VARIATION (PPV)

Pressure Variation (PPV) represents an interaction between lungs and heart. Ventilation (either spontaneous or mechanical) alters the intrathoracic pressure and causes stroke volume to vary. Greater variability in stoke volume (increased PPV) may suggest fluid responsiveness.



- Nick Mark MD @nickmmark



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