OXYGEN AND ACID-BASE PARAMETERS OF ARTERIAL AND MIXED VENOUS-BLOOD, RELEVANT VERSUS REDUNDANT

A complete pH and blood gas analysis of arterial and mixed venous bloo d may comprise more than forty different quantities. We have selected sixteen, including patient temperature. The arterial oxygen tension gr oup includes the oxygen tension, fraction of oxygen in inspired air, a nd fraction of mixed venous blood in the arterial (total physiological veno-arterial shunting). The haemoglobin oxygen capacity group includ es effective haemoglobin concentration and fractions of carboxy- and m ethaemoglobin. The haemoglobin oxygen affinity group includes half-sat uration tension and estimated 2,3-diphosphoglycerate concentration of erythrocytes. In a neonatal care unit fraction of fetal haemoglobin ne eds to be included. The arterial oxygen extractivity is measured as th e oxygen extraction tension, which indicates the degree of compensatio n among the oxygen tension, capacity, and affinity. The mixed venous g roup includes mixed venous oxygen tension, and, when measured, cardiac output, and oxygen consumption rate. The acid-base status includes bl ood pH, arterial carbon dioxide tension, and extracellular base excess . Other quantities such as haemoglobin oxygen saturation, respiratory index, total oxygen concentration (oxygen content), oxygen extraction fraction, oxygen delivery, and several others, provide no essential ad ditional clinical information and are therefore redundant.