Hemodynamic monitoring is one of the cornerstones of patient evaluation in the intensive care unit (ICU) and provides diagnostic and prognostic value. The choice of monitoring depends on the diagnostic needs of the patient and the risk-benefit balance of monitor placement and maintenance and complications associated with its use. This chapter outlines an approach to the assessment of hemodynamics and perfusion in patients who are critically ill and the technical principles of commonly used monitoring methods.

1. Perfusion:The goal of hemodynamic monitoring is to ensure adequate tissue perfusion for gas, nutrient, and waste exchange, with the goal of decreasing morbidity and mortality. It is difficult to link optimization of a single hemodynamic parameter to an improvement in morbidity and mortality. For this reason, intensivists should not rely solely on any one physical monitor or parameter but should evaluate multiple potential signs of adequate perfusion such as mental status, urine output, or laboratory findings (eg, central venous oxygen saturation, base deficit, and lactate).
2. Optimizing Perfusion:Hemodynamic monitors are not therapeutic. Hemodynamic data, however, can be used to guide therapy. Optimizing perfusion may require fluid administration, diuresis, administration of pharmacologic agents (eg, vasoconstrictors, inotropic agents), or interventions (eg, intra-aortic balloon pumps, ventricular assist devices, extracorporeal membrane oxygenation). With this in mind, any monitor must be used dynamically to ensure that employed therapies are optimizing perfusion over time.
1. Fluid challenge: Much discussion around optimization of hemodynamics revolves around fluid status. The “fluid challenge” is a time-honored test to aid in determining whether fluid administration could be beneficial. With a fluid challenge test, intravenous (IV) fluid is rapidly administered while hemodynamics are monitored to determine whether the administration improves hemodynamic parameters (and thereby be of benefit to the patient). Although the fluid challenge is not standardized, it most commonly involves the rapid administration of 500 mL of fluid, with a positive test defined as an increase in cardiac output (CO) greater than 10% to 15%. A “passive leg raise” test can be used to provide similar information. To perform this test, a clinician passively elevates a supine patient’s legs. Blood moves to the central veins from the elevated limbs, providing an “autotransfusion” of approximately 150 to 300 mL. An improvement in stroke volume suggests fluid responsiveness, whereas deterioration in hemodynamics can be quickly reversed by lowering the legs. A passive leg raise test may also be performed using pulse pressure as a surrogate for stroke volume. The sensitivity and specificity of a passive leg raise are reduced when changes in pulse pressure are measured in place of stroke volume.