Continuous measurement of oxygen consumption in fetal sheep

A microcomputer-based system has been developed to measure oxygen consumption continuously in fetal sheep. The system includes an umbilical artery electromagnetic blood flow transducer and two fiberoptic catheter oximeters for measuring umbilical artery and vein oxyhemoglobin saturation in vivo. The electrical signals from these instruments are digitized and sampled by a microcomputer. Fetal oxygen consumption is calculated from the Fick principle by use of the digitized signals and hemoglobin concentrations. The latter is measured intermittently and updated if necessary. System validation required that artifacts in oxyhemoglobin recordings could be avoided and that the catheter readings agreed with values from intermittent samples. Continuous heparin infusion and careful catheter placement facilitated attainment of these requirements. The system can be used to obtain continuous recordings of fetal oxygen consumption during rapidly occurring physiologic events.