[Monitoring of oxygen transport systems]

Abstract

The main task of the cardiorespiratory system is to deliver enough oxygen (O2) to meet the metabolic requirements of the body. Of all metabolic substrates, O2 has the highest percentage of extraction at 25%, and O2-reserves are therefore exhausted within a few minutes. Arterial O2-content and cardiac output (CO) are the determinants of O2-delivery (DO2). O2-delivery in intensive care patients and during the perioperative period can be compromised by many factors, especially diminished O2-uptake in the lung, reduced hemoglobin content, and/or altered cardiac performance. The quality of arterial oxygenation can now easily be monitored noninvasively by pulse oximetry and arterial blood gas analysis. To calculate DO2, however, determination of cardiac output, O2-tension, O2-saturation, and hemoglobin is necessary. Routinely measured hemodynamic parameters such as heart rate, systemic arterial pressure, etc. only poorly reflect O2-transport to the tissues. O2-consumption (VO2), the best mirror of the actual metabolic activities of the tissues, can be measured either noninvasively by the difference between inspiratory and expiratory O2-concentrations in connection with minute ventilation or invasively using arterial-venous O2-content difference and CO, which requires pulmonary artery catheterization. VO2 determination by respiratory gas analysis is very difficult at a high or changing FiO2.(ABSTRACT TRUNCATED AT 250 WORDS)