Method and apparatus for measuring the gaseous content of blood

Abstract

Method and apparatus for determining the gaseous content of a diluent, such as determining the oxygen or carbon dioxide content of blood. A sample of the diluent whose gaseous content is to be measured is anaerobically pumped past a junction tee after being placed in a reservoir. A second diluent, not part of the sample, is equilibrated with a gas (not the gas to be measured) in a first tonometer. This second equilibrated diluent is pumped past the junction tee where it is mixed with the diluent sample. The gas in the second diluent is selectively chosen to drive the gas to be measured into the dissolved phase. The diluent mixture is then allowed to flow through an appropriate sensor that senses the presence of the gas to be measured. This first measurement is stored in a suitable controller, such as a microprocessor. The controller, after causing the system to be flushed of all traces of the diluent sample, prepares a mixture of two selected diluents, such as first and second saline solutions, one of which is equilibrated in a tonometer to have 0% of the gas to be measured therein, and the other of which is equilibrated in another tonometer to have a known percent of the gas to be measured therein. The controller selectively controls the flow rates at which these two diluents are mixed, typically under the constraint that the flow rate of the mixture through the sensor is the same as was used in obtaining the first sensor measurement, until a second sensor measurement is obtained that is the same as the first sensor measurement. The gaseous content of the diluent sample may then be calculated based upon known physical measurements, such as flow rates, barometric pressure, and temperature.