A calcium clamp technique in man

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Abstract
Ca infusion imply a risk for cardiovascular complications. To avoid the risks, a new method for Ca infusion in man which can keep ionized Ca concentration in whole blood (WB-Ca2+) in a steady state at a predetermined level was developed. A solution of CaCl2 containing 0.117 mmol Ca2+/ml water, is infused i.v. by means of an IMED 922H infusion pump. WB-Ca2+ is determined every 5-10 min with a Ca2+-selective electrode, NOVA 2. The infusion rate is continuously adjusted. With the same initial infusion rate, 0.31 mmol Ca2+/kg b.w.[body weight]/hour, hypercalcemia that is WB-Ca2+ > 1.27 mmol/l was reached within 10 min in healthy volunteers, 8 females with a mean age of 26 yr (range 19-36) and 7 males with a mean age of 29 yr (range 25-34). The presettled WB-Ca2+ level, 1.45 mmol/l, was obtained within 25 min and maintained in a steady state for 155 min at 1.45 .+-. 0.01 mmol/l (mean .+-. SE) in the females, and at 1.46 .+-. 0.01 mmol/l in the males. The range of the individual steady state mean WB-Ca2+ was 1.42 .+-. 0.02 - 1.49 .+-. 0.02 mmol/l. No side effects of the infusion were noted except for a slight increase in systolic and diastolic blood pressure 60 min after start of the infusion. The Ca clamp technique is safe and suitable for such situations where a presettled easily controlled WB-Ca2+ level is required.