The Oxygen Status Algorithm on-line with the pH-blood gas analyzer

The Oxygen Status Algorithm is a computer program for interpretation of pH-blood gas measurements. Recently the facility for on-line transfer of measured data from the pH-blood gas analyzer (ABL 520) to the computer with instant calculation, graphical display, and print-out of the oxygen status and the acid-base status of the blood has been implemented.

To describe experiences with routine application of the Oxygen Status Algorithm in an intensive care unit and to describe recent improvements of the program.

Routine pH-blood gas analyses during a two year period with an average of 40 analyses per day.

Several unexpected results were disclosed, especially with respect to abnormal haemoglobin-oxygen affinity, causing suspicion of low 2,3-diphosphoglycerate concentration and hypophosphatemia. The criteria for routine administration of oxygen could be revised on the basis of the oxygen extraction tension. The program was expanded to allow the printing of a cumulated patient report, and modified to allow calculation of the oxygen consumption rate on the basis of simultaneous measurements on the arterial and the mixed venous blood. The program and the computer hardware functioned well in continuous operation during the whole study. It proved to be difficult, however, to ensure that all measurements were supplemented by information on the patient temperature and the fraction of inspired oxygen.

The Oxygen Status Algorithm provides a more detailed description of the oxygen status and the acid-base status of the blood than currently employed. The interaction between the arterial oxygen tension, the haemoglobin oxygen capacity and the haemoglobin oxygen affinity is displayed graphically and the degree of compensation among these three properties is expressed in terms of a single quantity: the oxygen extraction tension. The program also provides an interactive interpretation, allowing a rapid prediction of the expected effect of therapeutic intervention. Nevertheless, implementation of the program in the daily routine requires an intensive educational effort among physicians as well as nurses and laboratory technicians.