Noninvasive estimations of cardiac output and circulatory dynamics in critically ill patients

There is a need for noninvasive methods for estimating cardiac output that can be used outside the intensive care unit, particularly in the emergency department, intermediate care units, general hospital floors, doctors' offices, ambulances, and other prehospital areas. Advantages and limitations of the direct Fick method, echocardiography, and thoracic impedance cardiography are evaluated and compared with the standard thermodilution method. In general, noninvasive systems are safe, inexpensive, easy to operate, provide continuous on-line real-time display of data, and can be coordinated with other noninvasive systems to assess cardiac function, pulmonary function, and tissue perfusion. Moreover, the interactions of continuous streams of signals of multicomponent noninvasive systems may be analyzed by advanced information systems to evaluate evolving patterns of circulatory dysfunction, predict outcome, provide a decision support system, and improve patient care by earlier recognition and correction of circulatory problems.