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Contrast Media Adversely Affect Oxyhemoglobin Dissociation

Received from the Departments of Anesthesiology and Radiology, Illinois Masonic Medical Center, Chicago, Illinois; and the Departments of Anesthesiology and of Physiology and Biophysics, University of Illinois College of Medicine, Chicago, Illinois.

Abstract

Effects of ionic (Hypaque-76) and nonionic (Isovue-370 and Omnipaque-350) contrast media on oxyhemoglobin dissociation of normal human red blood cells were evaluated. In series 1, 4-mL venous blood samples were obtained from 15 normal human volunteers. One blood sample served as control, and 1 mL of either of the three contrast media was added in vitro to the other 4-mL blood samples. P₅₀ values were estimated from the linear portion of the oxyhemoglobin dissociation curve obtained by tonometry. Determinations of P₅₀ were performed at either pH 7.4 or 7.2. At pH 7.4, P₅₀ in the absence of contrast media was 26.3 ± 0.4 mm Hg (mean ± sem). The contrast media caused comparable decreases in P₅₀ from this value (Hypaque-76, 20.0 ± 0.5 mm Hg; Omnipaque-350, 21.6 ± 0.4 mm Hg; Isovue-370, 20.7 ± 0.4 mm Hg). Reducing pH to 7.2 in the absence of contrast media increased P₅₀ to 33.3 ± 1.0 mm Hg, evidence of the Bohr effect. The presence of contrast media either completely abolished (Hypaque-76 and Omnipaque-350) or markedly attenuated (Isovue-370) this effect. In series 2 (five patients), blood samples were withdrawn from the external iliac artery during injection of Isovue-370 (60–78 mL) into the proximal abdominal aorta to evaluate peripheral vascular disease. Measurement of P₅₀ of these samples yielded findings consistent with those of series 1. The present findings demonstrate that both ionic and nonionic contrast media increase the affinity of hemoglobin for oxygen and, therefore, that they may inhibit oxygen delivery to body tissues.

Key Words: OXYGEN, OXYHEMOGLOBIN DISSOCIATION—Contrast media. • BLOOD, HEMOGLOBIN—oxygen dissociation.