Shock Position

The shock position is used in the treatment of shock. It is also used as a diagnostic maneuver to assess fluid responsiveness, which is the probability that an individual will respond to therapy with intravenous (IV) fluids. Fluid therapy is often used in the treatment of shock to increase cardiac output and oxygen delivery to vital organs. However, only around 50% of individuals respond to fluid administration with a clinically significant increase in cardiac output. In addition, fluid overload can exacerbate pulmonary edema, precipitate respiratory failure, and prolong time spent on mechanical ventilation, which is why it is essential to determine which individuals experiencing shock will benefit the most from fluid administration. 

The passive leg raising (PLR) test uses gravity to pull venous blood from the lower body into the intrathoracic compartment, thereby increasing the volume of blood that returns to the heart (i.e., cardiac preload) by around 300 to 500 ml. The increase in cardiac preload leads to a temporary increase in stroke volume and cardiac output, which is similar to what happens during a fluid challenge where there is a rapid infusion of a small amount of IV fluids. The main drawback of the fluid challenge is that, if it is negative, fluid has already been administered to the individual, potentially causing fluid overload. Conversely, with the PLR, no fluids need to be administered, so there is no risk of fluid overload. 

A positive PLR test is when there is an increase of 10 to 15% in cardiac output following the leg raise, whereas a negative PLR test occurs when little to no changes in cardiac output are seen. Nonetheless, detection of fluid responsiveness by a positive PLR test may not always lead to fluid administration. Similarly, a negative PLR test may contribute to the decision to stop fluid infusion in order to avoid fluid overload, indicating that hemodynamic instability may be treated more appropriately with other measures, such as inotropic and vasopressor medications (e.g. norepinephrine, dobutamine, dopamine, etc.).

The shock position may not be suitable for individuals with traumatic brain injuries because passive leg raising could increase intracranial pressure. Other limitations include fractures of the lower extremities and leg amputations since these conditions can affect the volume of blood recruited by the maneuver.

The shock position, also known as passive leg raise, is a maneuver that recruits a portion of the venous blood from the legs and abdomen and shunts it towards the heart, causing a transient increase in cardiac output, which mimics the effect of IV fluid administration. This position can be used in the first aid of individuals with shock, but its main purpose is to assess fluid responsiveness in critically ill individuals so as to determine if they might benefit from IV fluid administration. The main advantage of this test is that it is simple and reversible, and since it does not require any IV fluid administration, there is no risk of fluid overload.