Passive leg raise

 Passive leg raise, also known as shock position.

PLR is a treatment for shock or a test to evaluate the need for further fluid resuscitation in a critically ill person.

Passive leg raise (PLR) is a physical maneuver or test performed to assess circulatory status and fluid responsiveness in patients. It involves raising a patient’s legs to an elevated position while they are lying down or in a semi-recumbent position, without any active leg movement from the patient.

During a passive leg raise, the legs are typically elevated to a 45-degree angle or higher, and the patient’s hemodynamic response is observed and measured. 

The purpose of a passive leg raise is to temporarily increase preload, which refers to the volume of blood returning to the heart. 

By elevating the legs, blood from the lower extremities is redistributed to the central circulation, increasing venous return. 

This increase in preload can help evaluate how the patient’s circulation responds and determine fluid responsiveness.

The response to a passive leg raise is measured by monitoring physiological variables such as blood pressure, heart rate, cardiac output, central venous pressure, or other markers of cardiac function. 

Passive leg raise is particularly useful in critical care settings, emergency departments, or during the initial assessment of patients with suspected volume depletion or septic shock. 

It can help guide medical decisions regarding fluid management and administration of vasoactive medications.

Raising the legs of a person without their active participation, causes gravity to pull blood from the legs, thus increasing circulatory volume available to the heart as cardiac preload, by around 150-300 milliliters, depending on the amount of venous reservoir.

The effects of this maneuver on hemodynamic parameters such as blood pressure and heart rate can be used to guide the decision whether or not more fluid will be beneficial.

The maneuver might be reinforced  by moving the patient’s bed from a semi-recumbent position to a recumbent position , with the legs raised. 

The maneuver may cause an additional mobilization 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. 

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. 

Passive leg raise requires increasing systemic venous return without altering cardiac function – a form of functional hemodynamic monitoring.

Studies suggest that PLR  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, does not work since bloodvessels are highly compliant, and expand as result of the increased volume locally. 

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