Osmolality of intravascular radiological contrast media

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Abstract
All current intravascular radiological contrast media are salts and produce solutions of very high osmolality, 5-8 times that of tissue cells, plasma or tissue fluid (all of which have an osmolality of 300 milliosmoles/kg H2O). Erythrocytes and vascular endothelium are adversely affected by the high osmolality of intravascular contrast media, resulting in tissue anoxia and increased capillary permeability, the latter causing damage to the blood-brain barrier. Vasodilatation, systemic hypotension and osmotic hypervolemia are generalized manifestations of the high osmolality of contrast media. New low osmolality contrast media were synthesized, utilizing a nonionizing radical (such as amide or amine) instead of the carboxyl group of a triiodinated substituted benzoic acid. Such examples are metrizamide (Amipaque) and Iopamidol (both nonionic amides) and Hexabrix (salts of a monoacid dimer). Early clinical evaluation suggests that these low osmolality solutions have major advantages in reducing pain, heat sensation and adverse reactions of angiography.