Background: The best way to resuscitate critically ill patients with fluids has been a hotly debated topic in the FOAMed and Critical Care worlds. Fluids are important to optimize stroke volume and distal tissue perfusion, however, the administration of excessive fluids for shock can increase a patient’s morbidity and mortality by causing volume overload, which may lead to tissue edema and subsequently inadequate blood flow to tissues . Accurately predicting when, whom, and how much fluid to administer remains a very challenging clinical question as only half of critically ill patients increase their cardiac output in response to the administration of fluids (i.e. the patient is preload or fluid responsive) .
Clinical signs and pressure/volumetric static variables are unreliable predictors of fluid responsiveness . Ventilator-induced dynamic variables such as stroke volume variation and pulse pressure variation, however, have been shown to be more accurate in predicating fluid responsiveness. These tests can only be applied when several criteria are present (e.g., sinus heart rate, mechanical ventilation with a tidal volume of 8-10cc/kg of ideal body weight).
Passive leg raise (PLR) is another method to assess preload responsiveness. PLR produces a temporary and reversible increase in ventricular preload through an increase in venous return from the lower extremities, which mimics fluid administration without actually having to give exogenous fluids. This sounds great in theory, but PLR requires a hemodynamic assessment to be made during the maneuver to determine if the patient is preload responsive or not. There are multiple techniques for assessing changes in stroke volume but the diagnostic performance of each method still remains unknown. The two most commonly described methods are changes in pulse pressure variation and variables of flow. Read more →