Clinical Applications of the Transpulmonary Thermodilution Technique

Abstract

In recent reviews of outcome, there is considerable evidence that mortality from high-risk surgery is often close to 10%, depending on case selection and operator experience. The inclusion of emergency work will often increase this figure to 20% [1, 2]. Whilst there is still no single definitive test to decide what is a high-risk case, it is possible to produce subgroups of patients who may be expected to do poorly. Tissue hypoperfusion during surgery has been shown to be a portent of poor outcome. Whatever the cause of this problem, be it poor cardiovascular performance or reduced intravascular volume, the link between alterations in microvascular flow and the onset of multiple organ dysfunction (MODS) is strong. In order to optimize fluid therapy it is necessary to have an appropriate method for measuring absolute values of flow or preload. Actually the current clinical standard of practice used to evaluate cardiac preload and to guide fluid administration during anesthesia includes monitoring of central venous pressure (CVP), invasive arterial pressure (AP) and, in selected high-risk patients, invasive cardiac output (CO), pulmonary artery pressure (mPA) and pulmonary artery occlusion pressure (PAOP) monitoring with pulmonary artery catheter (PAC) [3]. However, pressures can only serve as indirect indicators of filling volumes. They are as well influenced by intrinsic factors like cardiovascular compliance and patterns of myocardial relaxation as by extrinsic factors like positioning of the patients and, specifically in ventilated patients, changes in intrathoracic pressure. This might influence accuracy regarding cardiac preload estimation in specific clinical situations. Moreover, there is still controversy concerning indications and negative side effects attributed to this method [4, 5].