An ionized calcium regulated calcium clamp technique in man

A new method for calcium infusion in man is described. It is possible with this method to select, obtain and maintain a whole blood ionized calcium (WB-Ca++) level in a steady state by means of frequent ionized calcium determinations. Using the same initial calcium chloride infusion rate 17.55 mmol Ca++ per hour) in three groups of nor- mocalcemic patients (n = 23), hypercalcemia (i.e. WB-Ca++ > 1.32 mmol 1) was reached within 7-15 minutes; the desired level of WB-Ca++ (1.45 mmol 1) was obtained within 15-35 minutes. This level could then be maintained throughout the infusion period, 120 minutes. Thus, postmenopausal females with osteoporosis (n = 10) showed steady state WB-Ca++ levels of 1.46 ± 0.09 mmol 1 (mean ± s.d.), premenopausal females (n = 5) 1.45 ± 0.05 mmol 1 and males (n = 8) 1.43 ± 0.05 mmol 1. The difference between the mean WB-Ca++ for the steady state period and the desired level was ≤ 0.04 mmol 1 in each individual. With a coefficient of variation of ≤ 0.04 in each individual for WB-Ca++ during the steady state the physiologically active calcium fraction could be kept remarcably constant. No complications were noted during the infusion. The calcium clamp technique described is safe and suitable for purposes where a presettled, easily controlled WB-Ca++ level is needed in man.