Continuous Measurement of Po2, Pco2 and pH During Total Body Perfusion in Dogs

Abstract

Continuous measurement of blood P_o2, P_co2, and pH can be made either with intravascular electrodes or with electrodes placed in a flow cuvette. The two methods are reviewed. In this study a system based on the Radiometer flow cuvette was used. The continuous recording was checked at intervals against results obtained by conventional electrode analyses of individual blood samples. The continuous recording and individual checks were virtually identical. Checks on electrode calibration were made after 4–5 hours use, and no significant electrode drift was noted. During perfusion with Rygg-Kyvsgaard bubble-oxygenator, variations in P_o2, P_co2 and pH were measured continuously in dogs to register any changes, which might occur in the transition to and from perfusion, and which would be too rapid for measurement by the single sample technique. Apart from catheterization of the venae cavae through the right atrium the heart was undisturbed. In the first minutes of perfusion marked falls in all three parameters were observed. Oxygen tension fell on average by 168 mmHg, P_co2 by 17.3 mmHg and pH by 0.14. P_co2 rapidly returned to normal values, while pH and P_o2 increased slowly during the period of perfusion, an average of 69 min. Possible explanations of the changes are considered. On discontinuing perfusion P_co2 increased and pH fell. These changes may be partly explicable in terms of increase in dead space. The study indicates that variations in P_o2, P_co2 and pH not detectable by the individual sample technique can be registered by continuous measurement. Thus continuous measurement gives fine control and allows early correction of any disturbances, however rapid, in blood gases and pH.