A calcium clamp technique in man.

Calcium infusion imply a risk for cardiovascular complications. To avoid the risk, we have developed a new method for calcium infusion in man which can keep ionized calcium concentration in whole blood (WB-Ca++) in a steady state at a predetermined level. A solution of calcium chloride (Calcii chlor. Nord.), containing 0.117 mmol Ca++/ml water, is infused intravenously by means of an IMED 922H infusion pump. WB-Ca++ is determined every 5-10 min with a calcium ion-selective electrode, NOVA 2. The infusion rate is continuously adjusted. With the same initial infusion rate, 0.31 mmol Ca++/kg b.w./hour, hypercalcemia that is WB-Ca++ above 1.27 mmol/l was reached within 10 min in healthy volunteers, 8 females with a mean age of 26 years (range 19-36) and 7 males with a mean age of 29 years (range 25-34). The presettled WB-Ca++ 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 female and at 1.46 +/- 0.01 mmol/l in the males. The range of the individual steady state mean WB-Ca++ was 1.42 +/- 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. In conclusion, the calcium clamp technique is safe and suitable for such situations where a presettled easily controlled WB-Ca++ level is required.