Clinical Chemistry, Vol 1, 287-316, Copyright © 1955 by the American Association for Clinical Chemistry

Simultaneous Determination of pH, CO₂ Content, and Cell Volume in 0.1 ml. Aliquots of Cutaneous Blood

A Modification of the Shock and Hastings Technic

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1. A modificationhas been described for the Shock and Hastings technic of determining simultaneously, in 0.1 ml. aliquots of blood, the pH,CO₂. content, and packed cell volume. Advantages of the modification are collection and handling of the blood in a way that avoids the use of oil, and a modified design of the micropipets so that pH readings can be obtained in a filter photometer.

2. The standard error of measurement of a single reading was ±0.009 for the pH, and ±0.22mM/L. for the whole blood CO₂. concentration. The reproducibility of the photocolorimetric pH measurement was slightly better than that obtainable with the most accurate commercially available glass electrode.

3. Results have been presented to show that blood can be handled in the presence of brief, limited, exposure to air with no detectable change in pH and only negligible change in CO₂ content (decrease of less than 0.2 mM/L.). Errors attributable to collection and handling of cutaneous blood by this "virtual anaerobic" technic are not of significant magnitude.

4. Results have also been presented in confirmation of the fact that arterial and cutaneous blood are virtually identical in acid-base properties. A sample of as little as 0.5 ml. of cutaneous blood, analyzed by the microtechnic, provides the necessary and sufficient data for a description of the state of acid-base balance. This includes calculation of the physiologically important variables, arterial CO₂ pressure, and whole-blood buffer base concentration, thus furnishing a measure of the respiratory factor and the metabolic factor in any acid-base disturbance. With a sample size of 1.5 ml. it is also possible to determine other individual constituents of plasma, such as sodium, chioride, and total protein.

5. The technic is useful in the study of clinical disturbances of acid-base balance, especially in infants and children.

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