Serum ionized calcium by specific ion electrode

In 30 normal subjects whose sera were measured at 27° the pH was 7.46 ± 0.06 and the ionized calcium concentration by electrode was 3.86 ± 0.18 mg%. The precision was a relative S.D. of 2.2%. A series of reconstituted samples indicates that sera can be stored for several days in a refrigerator and if the pH is precisely restored to the fresh value by equilibration with carbon dioxide, the fresh ionized calcium will be restored.     

Facilitated determination of ionized calcium

Using a calcium-containing heparin preparation for anticoagulation, we determined [Ca2+], the mean concentration of ionized calcium, in whole blood of 120 healthy blood-donors to be 1.23 (SD 0.04) mmol/L. Similarly, for 50 intensive-care patients selected without conscious bias, the correlation between [Ca2+] in serum (mean 1.15, SD 0.10 mmol/L) and in whole-blood samples anticoagulated with the same heparin preparation (mean 1.15, SD 0.09 mmol/L) was very good (r = 0.95). Storing samples anaerobically on ice for as long as 2 h did not alter whole-blood [Ca2+]. On the other hand, various concentrations of calcium-free heparin preparations all induced a significant decrease in measured [Ca2+]. By using whole-blood samples, rather than plasma or serum, for [Ca2+] determination with a calcium-selective electrode, repetitive measurements can be made with simple handling procedures, facilitating rapid implementation of appropriate therapeutic measures for critically ill patients.     

Plasma ionized calcium in brain-dead patients

Background The mechanism of brain death-induced myocardial dysfunction remains debatable. Hypocalcemia is known to induce reversible myocardial dysfunction. However, the incidence of hypocalcemia and its effect on myocardial function during brain death is unknown.Methods In 54 consecutive braindead patients, we measured plasma total and ionized calcium concentrations, QT and corrected QT intervals, and left ventricular ejection fraction area (LVEFa), using transesophageal echocardiography.Results 49 (91%) of brain-dead patients had a decrease in total plasma total calcium concentration but only 19 (35%) had a decrease in plasma ionized calcium. Corrected total plasma calcium failed to predict ionized calcium concentration and QT intervals were not significantly different in normo and hypocalcemic patients. The LVEFa was not significantly different between normo and hypocalcemic patients (53±13 versus 50±20%), and no correlation was found between LVEFa and ionized calcium (R=0.02, NS). Hypocalcemic patients required greater doses of dopamine (8.2±5.2 versus 5.0±3.4 g·kg^–·min^–1,p<0.02) to maintain arterial pressure. Hypocalcemia was associated with a higher volume loading and a lower plasma protide concentration which reflected hemodilution.Conclusion A decrease in plasma ionized calcium is not frequent, rarely severe, and probably not the main mechanism of myocardial dysfunction in brain-dead patients. Hypocalcemic patients required higher doses of dopamine, suggesting a decrease in systemic resistance. Only direct measurement of ionized calcium can assess plasma calcium ion status in brain-dead patients.     

Serum ionized magnesium levels and serum ionized calcium/ionized magnesium ratios in women with menstrual migraine

OBJECTIVE: It has been suggested that magnesium deficiency may play an important role in menstrual migraine and that the serum ionized calcium (ICa2+)/ionized magnesium (IMg2+) ratio is important in migraine headache. Studies were designed to test these hypotheses. DESIGN: We prospectively evaluated 270 women seen at a headache clinic and in 61 women with menstrual migraine measured IMg2+, total magnesium, and ICa2+ levels so as to calculate the ICa2+/IMg2+ ratio. RESULTS: The incidences of IMg2+ deficiency were 45% during menstrual attacks, 15% during nonmenstrual attacks, 14% during menstruation without a migraine, and 15% between menstruations and between migraine attacks. The serum ICa2+ levels were within our reference range, but the ICa2+/IMg2+ ratio was elevated (P<.01) in menstrual migraine. CONCLUSIONS: The high incidence of IMg2+ deficiency and the elevated ICa2+/IMg2+ ratio during menstrual migraine confirm previous suggestions of a possible role for magnesium deficiency in the development of menstrual migraine.     

Serum ionized calcium by electrodes: new technology and methodology.

We report experience measuring serum ionized calcium (Ca2+) with new solid-state, specific calcium ion dip electrodes in a commercially available system for automated electrode measurments which permits stable measurements on thirty samples with up to six different electrodes simultaneously. The system provides electrostatic shielding, temperature regulation at 37degreeC, and adjustment of serum pH with CO2 gas, thereby making practical the use of serum standards and routine measurements on sera. When the electrodes are used with the rest of the measuring system and with serum standards, the system provides serum Ca2+ measurements with high precision (C.V. of 0.7%) and the calcium electrodes maintain good slopes for 50 to 150 hours of cumulative wet immersion. Response to new calcium activity is rapid, and wide variations in serum Ca2+ are readily measured.     

Heparinization of samples for plasma ionized calcium measurement

Maintenance of normal plasma ionized calcium concentration forms part of the management of the critically ill patient; it is, therefore, important to measure accurately plasma ionized calcium. We have compared the ionized calcium concentration of blood samples heparinized with a carefully measured amount of heparin with that of blood samples heparinized in the conventional fashion. The amount of heparin in the deadspace of a syringe was demonstrated to artifactually lower the plasma ionized calcium concentration. Samples for plasma ionized calcium measurement should be heparinized with a measured quantity of heparin, since the conventional technique introduces an unknown and probably excessive quantity of heparin into the syringe deadspace.     

Evaluation of AVL988/4 analyzer for measurement of ionized magnesium and ionized calcium

Ionized magnesium (Mg⁺⁺) and ionized calcium (Ca⁺⁺) are the physiologically active forms of these elements in the body and their concentrations have clinical value. Though the AVL988/4 instrument that measures concentrations of Mg⁺⁺ and Ca⁺⁺ has been evaluated, some clinically important parameters were unknown. In this study, we evaluated AVL988/4 analyzer for measuring Mg⁺⁺ and Ca⁺⁺ concentrations and provided the following information: (1) The newly formulated Becton Dickinson (BD) Vacutainer plastic tubes with clot activator and silicone as the stopper lubricant (serial no. 367820) caused a significant high bias for the Mg⁺⁺ measurement but had no effect on the Ca⁺⁺ measurement; (2) the optimal conditions for specimen storage were no exposure to air at 4°C for up to 24 h; (3) no significant difference in the results of the Ca⁺⁺ concentration determined using AVL988/4 or i-STAT; (4) no carryover between samples was found.     

Evaluation of AVL988/4 analyzer for measurement of ionized magnesium and ionized calcium

Ionized magnesium (Mg++) and ionized calcium (Ca++) are the physiologically active forms of these elements in the body and their concentrations have clinical value. Though the AVL988/4 instrument that measures concentrations of Mg++ and Ca++ has been evaluated, some clinically important parameters were unknown. In this study, we evaluated AVL988/4 analyzer for measuring Mg++ and Ca++ concentrations and provided the following information: (1) The newly formulated Becton Dickinson (BD) Vacutainer plastic tubes with clot activator and silicone as the stopper lubricant (serial no. 367820) caused a significant high bias for the Mg++ measurement but had no effect on the Ca++ measurement; (2) the optimal conditions for specimen storage were no exposure to air at 4 degrees C for up to 24 h; (3) no significant difference in the results of the Ca++ concentration determined using AVL988/4 or i-STAT; (4) no carryover between samples was found.     

Association between plasma ionized calcium and lactate concentration

Conclusion ISE are not suitable for the measurement of ionized calcium under clinical conditions when anions like acetate, lactate or malate are present in concentrations of about 5–10 mmol/l.     

Pharmacodynamic response to ionized calcium during acute sepsis

Ionized Ca (Ca2+) is essential for maintaining physiologic functioning in the cardiovascular system (CVS). Sepsis affects the CVS by several mechanisms and is associated with decreased serum Ca2+. The pharmacodynamic response of the CVS to serum Ca2+ alteration was compared in acutely septic and nonseptic dogs at serum Ca2+ levels of 50%, 100%, 150% and 200% of normal baseline values. Serum Ca2+ alterations caused similar changes in both groups, although finite differences existed between septic and nonseptic subjects. Ca manipulation produced limited differences in the response of mean arterial pressure, cardiac output, left ventricular dP/dtmax, systemic (SVR) and pulmonary (PVR) vascular resistance between septic and nonseptic subjects. PVR and SVR demonstrated opposite responses during hypocalcemia; PVR was lower than baseline in both groups, whereas SVR was higher at the 50% level. No difference was evident for total oxygen consumption (VO2) or heart rate. In view of the limited differences in response and the failure to improve systemic VO2, serum Ca2+ supplementation does not afford any additional benefit in this experimental model of acute sepsis.