Minimally invasive hemodynamic monitoring using the pressure recording analytical method.

The commonly employed reference techniques for assessment of cardiac output are represented by the direct Fick method in physiology, and by intermittent thermodilution in clinical practice. According to the Fick principle, cardiac output is determined by the ratio of oxygen uptake to the difference in oxygen content between arterial and mixed venous blood [1]. The validity of the method depends on the assumption that pulmonary blood flow closely approximates systemic blood flow and that lungs themselves do not extract oxygen. The major limitations of the method are the need for right heart catheterization to obtain truly mixed venous blood, the availability of techniques for measuring oxygen uptake and content, and the attainment of a steady state in which oxygen consumption matches tissue oxygen utilization [1, 2]. Likewise, the intermittent thermodilution method requires fulfillment of several conditions, such as complete mixing of the thermal indicator with blood, no loss of indicator within the dilution volume, and constant blood flow during the dilution time [3]. Inconsistency of these assumptions may occur in many clinical conditions, leading to inaccuracy in cardiac output measurements. In particular, variability of blood flow may result from hemodynamic instability related to changes in heart rate, cardiac arrhythmias, valvular or congenital heart disease, and application of mechanical ventilation [4]-[6]. © 2006 Springer Science + Business Media Inc.