Non-invasive, on-line measurement of oxygen consumption during anesthesia

Oxygen consumption is usually derived from values measured by a thermodilution catheter, i.e. an invasive procedure, with associated risks and calculation errors. Closed circuit ventilation provides a reliable, non-invasive means of access to this parameter of metabolism. Routine application of closed circuit ventilation requires overcoming many, mainly technical, difficulties (e.g. leakage problems, valve malfunctions, and calculations of gas uptake). We developed a computerized closed circuit anesthesia ventilator without these problems. With this system non-invasively measured oxygen uptake is continuously presented on-line. We discuss three representative patients presenting for surgical repair of an abdominal aneurysm. Besides actual changes in metabolism and depth of anesthesia, success or failure of the operation is visible in the pre- and direct post-clamping period. With resuscitative therapeutic interventions, increase in oxygen consumption gives valuable information under changing conditions. We conclude that closed circuit anesthesia is a safe and valuable method for measurement of oxygen consumption.