A multicomponent noninvasive monitoring system for high-risk critically ill patients was developed and tested in a series of 58 high-risk surgical patients. The system was comprised of a thoracic electric bioimpedance (TEB) method for cardiac output estimation, laser-Doppler velocimeter for small vessel flow, transcutaneous oxygen (PtcO2) sensor for tissue oxygenation, pulse oximeter for arterial hemoglobin saturation (SaO2) and finger pressor sensor for arterial pressure. In a series of critically ill patients, this noninvasive system was compared with the widely used invasive monitoring system with systemic and pulmonary artery catheters. Despite theoretical limitations of TEB as a measure of cardiac output, there was a satisfactory correlation (r = .83) of cardiac output measured by thermodilution (TD) and TEB throughout a wide range of severe illnesses. Moreover, changes in TEB cardiac output satisfactorily tracked changes in TD cardiac output (r = .91). There was poor correlation between TD cardiac output and BP or heart rate. The incidence of abruptly changing physiologic patterns was observed with simultaneously monitored invasive and noninvasive systems. Descriptions were made of the central circulation, peripheral perfusion, and pulmonary function; common interactive responses of these circulations were also evaluated. Monitored events defined as abrupt reductions in these variables often occurred from reduced cardiac output, PtcO2 or PtcO2/PaO2 index, and infrequently from unanticipated reductions in SaO2. Recovery from the nadir of the monitored event was associated usually with improvements in flow, PtcO2, or both. Hemodynamic and oxygen transport patterns of a few commonly encountered patterns are described.