INFLUENCE OF CHANGES IN IONIZED CALCIUM ON CARDIOVASCULAR REACTIVITY DURING HEMODIALYSIS

In order to prevent hypercalcemia due to the treatment of secondary hy perparathyroidism the use of low calcium dialysate is advocated. Howev er, as calcium ions play a pivotal role in both myocardial and vascula r smooth muscle contraction, lowering the dialysate calcium concentrat ion might result in a further impairment of the cardiovascular respons e during dialysis. Therefore, arterial blood pressure, forearm vascula r resistance (FVR) and venous tone (VT) (straing-gauge plethysmography ) as well as cardiac dimensions and output (echocardiography) were mea sured in IO hemodynamically stable dialysis patients (ejection fractio n >30%) during two standardized sessions of three-hour combined ultraf iltration-hemodialysis (UF+HD) at two different dialysate calcium conc entrations: 1.25 and 1.75 mmol/l. High calcium UF+HD resulted in a sig nificant increase in plasma ionized calcium (+0.19 +/- 0.11 mmol/l; p <0.01) while ionized calcium remained unchanged during low calcium UFHD (-0.02 +/- 0.07 mmol/l). As a result, systolic, diastolic and mean arterial blood pressure were respectively 14 +/- 10, 5 +/- 7 and 9 +/- 9 mmHg higher during high calcium UF+HD as compared to low calcium UF +HD (p <0.05). There were no significant differences in FVR and VT bet ween the two treatments. During both treatments FVR increased while VT decreased. In addition, there were no differences in calculated syste mic vascular resistance. However, with comparable end-diastolic dimens ions, stroke volume (-18 +/- 13 mi) and cardiac output (-1.3 +/- 1.5 l /min) decreased significantly (p <0.05) only during low calcium UF+HD. We conclude that even in hemodynamically stable patients changes in p lasma ionized calcium are an important determinant of the blood pressu re response during dialysis therapy. Whereas peripheral vascular react ivity is unaffected by changes in ionized calcium, myocardial contract ility is improved with higher dialysate calcium concentrations.