Why Do CAT Scans Often Cause a Warm Flush Sensation

1 Why Do CAT Scans Often Cause a Warm Flush Sensation  

Patients often report a warm, flushed feeling as one of the side effects of injection of a contrast medium in preparation for a CAT scan. What causes this rise in body temperature The answer lies in the ionic nature of the contrast medium and in the body s attempt to regulate the concentrations of all substances in the blood. 

Introduction of a water-soluble ionic substance into the vascular system results in an increase in the number of particles in the bloodstream as the contrast substance dissolves. The body possesses several internal regulation systems and, when perturbed by an injection, attempts to restore the concentrations of substances in the blood to their normal or preinjection levels. To re-equilibrate the system, water from the cells of surrounding body tissue moves into the blood plasma through capillary membranes. This transfer of water is an example of osmosis, the diffusion of a solvent (water) through a semipermeable membrane (the blood vessels) into a more concentrated solution (the blood) to equalize the concentrations on both sides of the membrane. To accommodate the increase in 

Some of the ionic iodinated substances used in CAT scans include amidotrizoates (salts of diatrizoic acid) and iothalamates (salts of iothalamic acid). The typical cations are sodium ion or meglumine (A-methyl-D-glucamine) ion (Fig. 10.1.1), 

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Why do CAT scans often cause a warm flush sensation See p. 128. 

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