Effect of metrizamide on whole blood oxygen affinity

The effects on whole blood oxygen affinity following addition to human blood of either ionic (diatrizoate) or non-ionic (metrizamide) contrast medium were investigated in vitro. No medium changed whole blood oxygen affinity. Solutions of metrizamide produced less changes in plasma pH than solutions of diatrizoate. This difference is explained by lower buffer capacity and lower osmolality of metrizamide solutions. Low osmolality gives less redistribution of anions between plasma and red cells and therefore less decrease in plasma pH.