Applications of minimally invasive cardiac output monitors

The ultimate goal of any hemodynamic monitoring system is to provide the clinicians with additional information on the underlying pathological condition and to guide fluid or vasopressor therapy. Cardiac output measurement and its response to therapeutic interventions are frequently used in critically ill patients. As the use of CO monitoring devices increases today, it is necessary to understand the application of such devices in different clinical settings. For many years pulmonary artery catheter (PAC) thermodilution cardiac output assessment was the monitor of choice for the management of critically ill patients. Thermodilution is a modification of the original indicator dilution techniques in which the injectate has a defined volume and temperature from which the thermodilution curve is generated [1]. As with the other indicator dilution techniques, CO is calculated from the area under the indicator thermodilution curve using the modified Stewart-Hamilton equation [2]. PAC was first used in dogs, and subsequently in humans 50 years later [2]. PAC provides valuable measurements, including right atrial pressure, right ventricular pressures, pulmonary artery pressures, pulmonary artery occlusive pressure, mixed venous saturation (SvO2), and CO. The derived hemodynamic variables are systemic and pulmonary vascular resistances. The major obstacle for the use of PAC has been the lack of demonstrating patient benefit and its level of invasiveness. Several prospective trials have demonstrated the lack of benefit from PACs. The PAC-man trial indicated that the routine placement of PACs had no effect on morbidity or mortality, and the ESCAPE trial found no difference in mortality or length of hospital stay when PAC parameters were compared with clinical assessment in the management of severe congestive heart failure patients [3-6]. Furthermore, for using PAC now, many physicians have lost the training, confidence, and familiarity with its use. PAC should probably be used