Evaluation of Error in Measurement of pH of Blood at Room Temperature

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BLOOD pH values obtained in vitro vary as inverse functions of the temperature of the specimen. These variations are sufficiently great that values determined on blood at room temperature must be corrected to have clinical significance. Ideally, measurements of blood pH should be made at body temperature, and the modern manufacture of instruments is now rapidly providing the means for such measurements. But many determinations are still made at room temperature, and then are corrected to yield what is presumed to be true in vivo pH values.

Rosenthal1 as well as Craig, Lange, Oberman, and Carson2 studied the effect of temperature on blood pH, and in each study a formula was derived that purported to allow accurate corrections to be made. These formulas are shown in Table 1 in which pH37 and pH38 are the values at 37 and 38 C., respectively, and pHt is the value observed at room temperature. Objections have been raised to this practice of measuring blood pH at room temperature and then correcting the observed values by means of one of the formulas. The objections are based on the possible variations in the responses of specimens from different persons to changes in temperature.1–3 The total number of persons from whom specimens were obtained for examination in two independent studies1,2 was only 46, which probably is insufficient to appraise the full potential error of the technic.

The work presented here involves blood specimens from 243 patients. The findings confirm the observations of other workers that . . .



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