A small sample of blood from the ear lobe or the fingertip is adequate for pH measurement in clinical situations. The pH of blood from the warmed ear lobe accurately reflected arterial pH in 43 patients. The acute changes in arterial pH produced by induction of respiratory acidosis and respiratory alkalosis were correctly measured by blood from the ear lobe. The pH of fingertip blood closely approximated arterial pH in 19 patients. To fully evaluate the patient with an acid-base imbalance, one needs both pH and venous carbon dioxide content. The latter is readily available now. We want to encourage doctors to make direct measurements of pH in patients by using fingertip or ear lobe blood.
McDonald JS, Laughlin DE, Bedell GN. Direct Approach to Evaluation of Patients With Acid-Base Imbalance. JAMA. 1964;188(1):9–11. doi:10.1001/jama.1964.03060270015003
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