Quantitative effects of osmotic diuresis following angiographic contrast administration

Osmotic diuresis resulting from the administration of angiographic contrast poses the potential threat of marked volume losses obligated by the renal excretion of non-reabsorbable solute. We prospectively assessed urinary excretion of solute and water following cardiac angiography in 14 euvolemic subjects without preexisting renal disease, by a protocol that allowed each patient to serve as his own control. During the initial 6 h after the beginning of angiography, contrast administration resulted in increased total osmolar excretion from a control rate of 0.79 ± 0.09 to 1.09 ± 0.09 mOsm/min (P <.05) with a return to control values thereafter. Surprisingly, sodium, potassium, and chloride excretion rates did not differ significantly from control values. After subtraction of the molar contribution of electrolytes, urea, and creatinine from the total osmolar excretion rate, it was apparent that the “residual osmolar excretion rate” of 0.48 ± 0.05 mOsm/min was markedly elevated over the control value of 0.11 ± 0.05 mOsm/min (P <.01), reflecting the excretion of contrast agent. Despite the marked osmotic diuresis, urine output during this period (3.9 ± 0.2 cc/min) did not differ significantly from the control value of 4.0 ± 0.3 cc/min. We conclude that marked volume losses are not a necessary concomitant of contrast-induced osmotic diuresis in the euvolemic cardiac patient without renal disease.