Perfusion Index or PI is the ratio of the pulsatile blood flow to the non-pulsatile static blood flow in a patient's peripheral tissue, such as finger tip, toe, or ear lobe. Perfusion index is an indication of the pulse strength at the sensor site. The PI's values range from 0.02% for very weak pulse to 20% for extremely strong pulse. The perfusion index varies depending on patients, physiological conditions, and monitoring sites. Because of this variability, each patient should establish his own "normal" perfusion index for a given location and use this for monitoring purposes.