Nomograms for correction of blood Po2, Pco2, pH, and base excess for time and temperature.

Abstract

Errors in the measurement of blood PO2, PCO2, pH. and base excess arise from two main sources metabolic changes which occur between sampling and measurement, and temperature differences between the experimental subject and the measuring electrode. Nomograms have been constructed to simplify the necessary corrections for these errors. These are as follows: cor-rections to PCO2, PO2, pH, and base excess for elapsed time, based on the assumption that blood is withdrawn from a normothermic sub- ject, and allowed to cool spontaneously towards an ambient temperature of 20-24 C, and similar corrections based on the assumption that the syringe is maintained at 37 C between sampling and analysis; corrections to PCO2, PO2, and pH for temperature differences between the electrode and the subject; the pH-temperature coefficient allowing for the dependance of this coefficient on pH and PCO2; and line charts representing the normal oxyhemoglobin dissociation curve and the corrections necessary to make this applicable to various temperatures and acid-base states. This chart is necessary since the effect of temperature on PO2 depends upon the percentage saturation.