Cardiac output and intravascular volume

It is absolutely necessary to conclude that the blood in the animal body is impelled in a circle, and is in a state of ceaseless motion; that this is the act or function which the heart performs by means of its pulse; and that it is the sole and only end of the motion and contraction of the heart. William Harvey (1578–1657) Introduction The management of a hemodynamically unstable patient is one of the most challenging experiences for the acute care physician; incorrect treatment or delay in appropriate treatment can result in morbidity and mortality. Anesthesia- and sepsis-induced changes in arterial or venous tone, intravascular volume, ventricular performance, peripheral vascular reactivity, core temperature, and blood rheology sum to make the moment-to-moment assessment of cardiovascular status difficult. Monitoring the heart rate and blood pressure may be adequate for many patients, but in a milieu of cardiovascular abnormality, more detailed measurements are needed, as the cardiovascular system is too complex for assessment with something as ingenuous as heart rate and systemic blood pressure.