Invasive haemodynamic monitoring: concepts and practical approaches.
The goal of haemodynamic care is to ensure adequate organ blood flow and oxygen supply. Clinical signs of organ perfusion have limited value in estimation of tissue perfusion, but invasive haemodynamic monitoring is needed to gain information of the underlying pathological condition and to guide oxygen delivery and haemodynamic therapy. Many of the available haemodynamic measurements involve pulmonary artery (PA) catheterization. Pressure measurements from PA catheters require meticulous attention to the dynamic properties of the transducer-pressure line system and appreciation of pressure variation owing to respiration. New techniques of continuous measurement of mixed venous oxygen saturation and cardiac output provide valuable trend data, allowing immediate diagnosis and treatment of pathological changes. Fast-response thermistor PA catheters are useful tools for estimating right ventricular function. Although clinicians generally regard PA-catheter data as a valuable therapy guide, few studies showing the beneficial influence on overall outcome have been carried out, and some studies have reported suboptimal understanding and utilization of these data. Transoesophageal echocardiography (TEE) is also a valuable monitor of left ventricular systolic and diastolic function and myocardial ischaemia in anaesthetized patients and in intensive care settings, but it requires a trained operator and is time-consuming. Continuously displayed TEE data, obtainable with automatic border detection, will make TEE even more useful in the near future. More effective monitors of perfusion and oxygenation of individual organs are needed. Less invasive techniques are also constantly sought. Combining data from several noninvasive monitors, including measurements of pulse oximetric O2 saturation, transthoracic impedance cardiac output and transcutaneous oxygen tension, has been reported to reflect closely changes obtained with more invasive monitoring.