Pulse Pressure Variation and Volume Responsiveness
Assessing volume status in the critically ill is extremely challenging, as up to 50% of patients do not respond to a fluid challenge (i.e. increase their stroke volume/cardiac output with additional IVFs).
As highlighted in previous pearls, traditional measurements such as blood pressure, heart rate, and urine output are extremely variable and inaccurate in determining volume status.
Pulse pressure variation is an emerging method of volume assessment that, to date, seems even better than ultrasound measurements of the IVC.
To calculate PPV, print out a tracing from an arterial line that captures both inspiration and expiration use the following formula:
ΔPP = 100 × (PPmax - PPmin)/[(PPmax + PPmin)/2]
Values > 13% indicate that the patient is likely on the ascending portion of their Starling Curve and will augment their cardiac output with additional IVFs.
Note that arrhythmias and spontaneous breathing can affect measurements, thus patients should be mechanically ventilated and well sedated when measuring PPV.
References
Marik PE, Cavallazzi R, Vasu T, Hirani A. Dynamic changes in arterial waveform derived variables and fluid responsiveness in mechanically ventilated patients: A systematic review of the literature. Crit Care Med 2009;37(9):2642-7.
