Passive leg raise, also known as shock position, is a treatment for

shock Shock may refer to: Common uses Collective noun *Shock, a historic commercial term for a group of 60, see English numerals#Special names * Stook, or shock of grain, stacked sheaves Healthcare * Shock (circulatory), circulatory medical emergen ...

or a test to evaluate the need for further fluid resuscitation in a

critically ill Intensive care medicine, also called critical care medicine, is a medical specialty that deals with seriously or critically ill patients who have, are at risk of, or are recovering from conditions that may be life-threatening. It includes pro ...

person. It is the position of a person who is lying flat on their back with the legs elevated approximately . The purpose of the position is to elevate the legs above the heart in a manner that will help blood flow to the heart. This test involves raising the legs of a person's (without their active participation), which causes

gravity In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...

to pull

blood Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in the cir ...

from the legs, thus increasing circulatory volume available to the

heart The heart is a muscular organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon dioxide to t ...

( cardiac preload) by around 150-300

milliliter The litre (international spelling) or liter (American English spelling) (SI symbols L and l, other symbol used: ℓ) is a metric unit of volume. It is equal to 1 cubic decimetre (dm3), 1000 cubic centimetres (cm3) or 0.001 cubic metre (m3). ...

s, depending on the amount of venous reservoir. The real-time effects of this maneuver on

hemodynamic Hemodynamics or haemodynamics are the dynamics of blood flow. The circulatory system is controlled by homeostatic mechanisms of autoregulation, just as hydraulic circuits are controlled by control systems. The hemodynamic response continuously mo ...

parameters such as blood pressure and

heart rate Heart rate (or pulse rate) is the frequency of the heartbeat measured by the number of contractions (beats) of the heart per minute (bpm). The heart rate can vary according to the body's physical needs, including the need to absorb oxygen and excr ...

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 An arterial line (also art-line or a-line) is a thin catheter inserted into an artery. Use Arterial lines are most commonly used in intensive care medicine and anesthesia to monitor blood pressure directly and in real-time (rather than by i ...

). The maneuver might be reinforced in a clinical setting by moving the patient's bed from a semi-recumbent (half sitting, half laying down) position to a recumbent (laying down) position with the legs raised. This is theorised to cause an additional mobilisation of blood from the gastrointestinal circulation. Direct measurement of cardiac output is the more reliable comparing to the measurement of blood pressure or pulse pressure because of pulse pressure amplification during this procedure. Cardiac output can be measured by arterial pulse contour analysis, echocardiography, esophageal Doppler, or contour analysis of the volume clamp-derived arterial pressure. Any bronchial secretions must be aspirated before performing this test. The legs should not be elevated manually because it may provoke pain, discomfort, or awakening that can cause adrenergic stimulation, giving false readings of cardiac output by increasing heart rate. After the maneuver, the bed should be placed back into semi-recumbent position with cardiac output measured again. The cardiac output should return to the values measured before the initiation of this maneuver. This test can be used to assess fluid responsiveness without any fluid challenge, where the latter can lead to fluid overload. Compression stockings should be removed before the test so that adequate volume of blood will return to the heart during the maneuver. 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. Placing the person in the

Trendelenburg position In the Trendelenburg position, the body is lain supine, or flat on the back on a 15–30 degree incline with the feet elevated above the head. The reverse Trendelenburg position, similarly, places the body supine on an incline but with the head ...

, does not work since bloodvessels are highly compliant, and expand as result of the increased volume locally. More suitable would be the use of

vasopressors An antihypotensive agent, also known as a vasopressor agent or simply vasopressor, or pressor, is any substance, whether endogenous or a medication, that tends to raise low blood pressure. Some antihypotensive drugs act as vasoconstrictors to in ...

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See also