Intravascular oxygen monitoring with a polarographic oxygen cathode

Thin flexible oxygen cathodes coated with heparin-dispersed cellulose diacetate were prepared for an intravascular monitoring of blood pO2. The effect of the thickness of cellulose diacetate on various characteristics of the cathode, such as its sensitivity, response, residual current, moving artefact, linearity, and protection against poisoning, were measured. Coating with six to ten layers of 7.5% cellulose diacetate resulted in a high level of protection for cathode against poisoning by blood constituents, while still leaving a sufficiently rapid response. An instillation system using heparinized saline has been designed for further prevention of local blood coagulation. At the same time this system maintains a stable conductance of the salt bridge and furthermore, enables in vivo calibration of the cathode sensitivity by supplying an instillation solution of a known oxygen tension. Using this electrode system, various intravascular pO2 measurements have been carried out, and one representative result is shown. The advantages and disadvantages of this type of separated electrode system compared with the combined type electrode are also discussed in detail.