In medicine, the passive leg raising test is a bedside test to evaluate the need for further fluid resuscitation in critically ill patients.
This test involves raising the legs of a patient (without their active participation), which causes gravity to pull blood from the legs, thus increasing circulatory volume available to the heart (cardiac preload) by around 150-300 milliliters, depending on the amount of venous reservoir. The real-time effects of this maneuver on hemodynamic parameters such as blood pressure and heart rate are used to guide the decision whether or not more fluid will be beneficial. The assessment is easier when invasive monitoring is present (such as an arterial catheter).
The maneuver might be reinforced in a clinical setting by moving the patient's bed from a semi-recumbent position to a recumbent position with the legs raised. This is theorised to cause an additional mobilisation of blood from the gastrointestinal circulation. The physiology of assessing fluid responsiveness via passive leg raise requires increasing systemic venous return without altering cardiac function - a form of functional hemodynamic monitoring.
Several studies showed that this measure is a better predictor of response to rapid fluid loading than other tests such as respiratory variation in pulse pressure or echocardiographic markers.