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.     

A simple method for determining physiologically active calcium and magnesium concentrations in critically ill patients

Total serum calcium and magnesium concentrations are frequently abnormal in critically ill patients despite the occurrence of normal ionized levels. Since ultrafilterable calcium and magnesium values approximate ionized levels, we evaluated the accuracy of ultrafilterable levels in critically ill patients. Ultrafilterable serum calcium concentrations were sensitive (95%) and specific (93%) in predicting ionized hypocalcemia. Total serum calcium values were sensitive (93%) but lacked specificity (50%) in predicting ionized hypocalcemia. Total serum magnesium concentrations were sensitive (100%) but not specific (73%) in predicting ultrafilterable hypomagnesemia. We conclude that ultrafilterable calcium concentrations offer an alternative to ionized calcium measurements when an ion-selective electrode is not available. In addition, ultrafilterable magnesium levels may reflect more accurately the true ionized magnesium concentrations than total serum magnesium values.     

Calcium and magnesium in essential hypertension

1. Because disturbances of calcium metabolism have been described in hypertension, measurements of plasma and serum concentrations of ionized calcium, total calcium, magnesium and renin were made in 38 patients with essential hypertension and age- and sex-matched control subjects. Urinary excretion of calcium, magnesium and sodium was also determined. 2. The mean serum concentration of ionized calcium was 1.23 +/- 0.04 (SD) mmol/l in the hypertensive group and 1.21 +/- 0.03 mmol/l in controls, and results were similar after correction for pH. There was a weak positive correlation between serum ionized calcium (pH 7.4) and systolic pressure (r = 0.26, P less than 0.02), but no correlation with plasma renin concentration. 3. Although the difference between serum total calcium concentration in the hypertensive (2.29 +/- 0.09 mmol/l) and control (2.26 +/- 0.07 mmol/l) subjects was not significant, there was a significant correlation between total calcium and systolic pressure (r = 0.23, P less than 0.05) which was maintained after correction for other variables. 4. There were no differences in plasma concentrations of parathyroid hormone or 1,25-dihydroxycholecalciferol between hypertensive and control subjects. 5. The hypertensive group showed higher urinary excretion of calcium (5.9 +/- 3.0 mmol/24 h) than controls (4.6 +/- 1.7 mmol/24 h), but the difference was not maintained after correction for sodium excretion. 6. Serum concentrations of magnesium were similar in the two groups, but urinary excretion of magnesium was significantly lower in hypertensive (3.7 +/- 1.3 mmol/24 h) than control (4.5 +/- 1.6 mmol/24 h) subjects and there was an inverse correlation between magnesium excretion and blood pressure (r = 0.3-0.35, P less than 0.01).     

Foscarnet-induced changes in plasma concentrations of total and ionized calcium and magnesium in HIV-positive patients

The time course and magnitude of foscarnet-induced changes in plasma concentrations of total and ionized calcium and magnesium were investigated in 13 male HIV-positive patients who had no active cytomegalovirus-associated disease. The patients had a mean age of 36 years (range 25-49 years) and a mean CD4 cell count of 550 cells/mm3 (range 130-1280 cells/mm3). Peak (mean +/- SD) plasma concentrations of foscarnet (0.89+/-0.10 mmol/l) were seen at the end of the period of drug infusion (90 mg/kg of foscarnet was infused over 2 hours) and declined with a terminal half-life of 5.7+/-0.7 hours. Plasma concentrations of total calcium declined over an 8-hour period, with the lowest concentration occurring after 4 hours (baseline: 2.29+/-0.09 mmol/l; lowest: 2.18+/-0.07 mmol/l; P < 0.001). By contrast, the lowest plasma concentration of ionized calcium occurred after 2 hours (baseline: 1.25+/-0.04 mmol/l; lowest: 0.99+/-0.05 mmol/l; P < 0.001), before gradually recovering to baseline levels over the next 10 hours. The mean maximal decrease in total calcium was 0.11+/-0.06 mmol/l, compared with 0.26+/-0.04 mmol/l for ionized calcium (P < 0.001). Plasma concentrations of total magnesium declined from 0.79+/-0.06 mmol/l (baseline) to 0.74+/-0.04 mmol/l (P < 0.05) after 4 hours and remained at this level after 8 hours. However, plasma concentrations of ionized magnesium fell steeply from 0.56+/-0.03 mmol/l to 0.39+/-0.03 mmol/l at 2 hours (P < 0.001), followed by a gradual recovery over the next 10 hours. The mean maximal decrease in total magnesium was 0.05+/-0.08 mmol/l, compared with 0.18+/-0.03 mmol/l (P < 0.001) for ionized magnesium. In summary, we found that foscarnet-induced changes in the plasma concentrations of total calcium and magnesium were dissociated from the corresponding changes in ionized calcium and magnesium. The maximal decreases in the plasma concentrations of total calcium and magnesium were smaller in magnitude and occurred much later than did the changes in ionized calcium and magnesium. The relative changes in the plasma concentration of ionized magnesium were greater than those of ionized calcium, indicating that foscarnet binds preferentially to the magnesium ion.     

Influence of blood sampling techniques on ionized magnesium level

The aim of the study was to evaluate whether different blood sampling techniques (venous vs. capillary) influence the level of ionized magnesium. A total of 12 men and 20 women were included. A venous blood sample was collected from the antecubital vein without stasis in syringes containing 50 IU/ml electrolyte balanced heparin. Capillary tubes containing sodium heparin 50 IU/ml were used for blood sampling (150 microl) from the earlobe. A statistically significant difference between venous and capillary ionized magnesium at actual pH (0.57+/-0.04 vs. 0.55+/-0.04 mmol/L, p<0.05) was observed, whereas no difference was seen between adjusted ionized magnesium. No difference was observed between venous and capillary ionized calcium at actual pH or adjusted to pH 7.4. The pH level was significantly higher in capillary blood (7.44+/-0.02 vs. 7.48+/-0.02. p<0.00001). The higher pH in capillary blood may be due to greater exposure to air in capillary tubes, and this most likely explains the observed difference between venous and capillary ionized magnesium at actual pH.     

Analysis of the brain bioavailability of peripherally administered magnesium sulfate: A study in humans with acute brain injury undergoing prolonged induced hypermagnesemia

OBJECTIVE: Based on preclinical investigations, magnesium sulfate (MgSO4) has gained interest as a neuroprotective agent. However, the ability of peripherally administered MgSO4 to penetrate the blood-brain barrier is limited in normal brain. The current study measured the passage of intravenously administered Mg into cerebrospinal fluid in patients with brain injury requiring ventricular drainage. DESIGN: A prospective evaluation of the cerebrospinal fluid total and ionized magnesium concentration, [Mg], during sustained hypermagnesemia was performed. SETTING: Neurosciences intensive care unit at a major teaching institution. PATIENTS: Thirty patients with acute brain injury secondary to subarachnoid hemorrhage, traumatic brain injury, primary intracerebral hemorrhage, subdural hematoma, brain tumor, central nervous system infection, or ischemic stroke were studied. INTERVENTIONS: Patients underwent 24 hrs of induced hypermagnesemia during which total and ionized cerebrospinal fluid [Mg] was measured. Serum [Mg] was adjusted to 2.1-2.5 mmol/L. Cerebrospinal fluid [Mg] was measured at baseline, at 12 and 24 hrs after onset of infusion, and at 12 hrs following infusion termination. MEASUREMENTS AND MAIN RESULTS: At baseline, total (1.25 +/- 0.14 mmol/L) and ionized (0.80 +/- 0.10 mmol/L) cerebrospinal fluid [Mg] was greater than serum total (0.92 +/- 0.18 mmol/L) and ionized (0.63 +/- 0.07 mmol/L) [Mg] (p < .05). Total (1.43 +/- 0.13 mmol/L) and ionized (0.89 +/- 0.12 mmol/L) cerebrospinal fluid [Mg] was maximally increased by 15% and 11% relative to baseline, respectively, during induced hypermagnesemia (p < .05). CONCLUSIONS: Hypermagnesemia produced only marginal increases in total and ionized cerebrospinal fluid [Mg]. Regulation of cerebrospinal fluid [Mg] is largely maintained following acute brain injury and limits the brain bioavailability of MgSO4.     

The simultaneous measurement of ionized and total calcium and ionized and total magnesium in intensive care unit patients

PURPOSE: This study was undertaken to determine the relationship between total magnesium and ionized magnesium in critically ill and injured patients. METHODS: Eighty consecutive intensive care unit (ICU) admissions were evaluated and 34 patients were enrolled in the study. Patients were enrolled who had indwelling arterial catheters and were within 4 days of ICU admission. Six milliliters of blood was collected and assayed simultaneously for total and ionized magnesium, total and ionized calcium, and albumin level. An Acute Physiology and Chronic Health Evaluation (APACHE II) score was calculated at the time of blood collection. RESULTS: The results of our study show a strong correlation between ionized and total magnesium (R =.903) that was not seen between ionized and total calcium (R =.748). We found total hypomagnesemia in 18% and ionized hypomagnesemia in 21% of ICU patients. We also found that 14.7% (5 of 34) of our patients had ionized hypermagnesemia whereas none displayed total hypermagnesemia. We did not find a correlation between APACHE II, sex, race, albumin level, and any electrolyte level. The mortality rate in the subjects studied was 21% (7 of 34). CONCLUSIONS: Based on our results we would recommend that intensivists directly measure ionized calcium whereas ionized magnesium can be inferred from total magnesium.     

A direct relationship between ionized calcium and arterial pressure among patients in an intensive care unit

Serum ionized calcium (Ca+2), creatinine, magnesium, phosphate, and arterial pH were measured in patients on admission to the medical ICU (MICU). Patients were classified into three groups: a) hypotensive (n = 38), those who received vasopressor support for frank hypotension; b) hypertensive (n = 21), those who required vasodilator therapy; and c) normotensive (n = 53), those who required neither vasopressor nor vasodilator therapy. Analysis of variance revealed that only Ca+2, creatinine, and arterial pH differed among the three groups. The difference in Ca+2 persisted when analysis of variance was repeated with creatinine as a covariate. Hypotensive patients had a significantly (p less than .05) lower mean Ca+2 (1.04 +/- 0.13 mmol/L) than normotensive patients (1.13 +/- 0.10 mmol/L), who in turn had a significantly (p less than .05) lower Ca+2 than hypertensive patients (1.18 +/- 0.09 mmol/L). Ca+2 correlated with mean arterial pressure at the time of serum collection (n = 118; r = .43; p less than .01), independent of any other variable. Vasopressor support was required in 41% of hypocalcemic patients in comparison to 14% of normocalcemic patients (p less than .01). Vasodilator therapy was required for 34% of normocalcemic patients, compared to 7.5% of hypocalcemic patients (p less than .01). There appears to be a clinically significant association between hypotension and hypocalcemia. This association may or may not be causal.     

Placebo-controlled study of intravenous magnesium supplementation during large-volume leukapheresis in healthy allogeneic donors

BACKGROUND: Marked decreases in ionized magnesium (iMg) levels occur during large-volume leukapheresis (LVL); however, the effect of intravenous (IV) magnesium supplementation in this setting has not been carefully studied. STUDY DESIGN AND METHODS: Thirty healthy allogeneic peripheral blood progenitor cell donors receiving citrate anticoagulant with IV calcium prophylaxis were randomized to receive either IV magnesium (0.2 mg Mg per mL acid citrate dextrose-A) or placebo during LVL, with a double-blind design. RESULTS: Thirty subjects underwent 75 LVL pro- cedures, 37 with magnesium and 38 with placebo. Group characteristics were similar for sex, weight, citrate infusion rate (1.36 mg/kg/min vs. 1.37 mg/kg/min), and volume processed (16 L vs. 17 L). Serum iMg levels remained within the reference range with magnesium supplementation, but decreased 39+/-11 percent below baseline (p<10(-10)) after placebo, with greater decreases after consecutive procedures. Subjects receiving magnesium had more vigorous parathyroid hormone responses and higher glucose levels and also tended to have higher serum potassium and ionized calcium levels. Mild paresthesias, coldness, and nausea occurred in 28, 20, and 7 percent of donors, respectively, with no significant differences between groups. Severe symptoms (chest tightness) occurred in only one subject receiving placebo. CONCLUSION: IV magnesium supplementation exerts a significant impact on serum magnesium levels, but does not reduce the frequency or severity of the relatively mild citrate-related effects observed in LVL performed with continuous IV calcium prophylaxis.     

Albumin-adjusted calcium is not suitable for diagnosis of hyper- and hypocalcemia in the critically ill

OBJECTIVE: To evaluate whether calcium adjusted for albumin can be used to monitor calcium homeostasis in critically ill patients. DESIGN: Prospective single-single center observational study. SETTING: Clinical laboratory and critical care unit of a regional teaching hospital. PATIENTS: Fifty-three paired samples were from 36 patients requiring intensive care treatment. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Total calcium, albumin-adjusted calcium, and ionized calcium were measured in critically ill patients during an 8-wk period. Calcium was adjusted for albumin using the formula that is most frequently used in The Netherlands. Using ionized calcium as the gold standard, albumin-adjusted calcium overestimated hypercalcemia and totally missed hypocalcemia. The same seemed to be true for other formulas used for albumin or protein adjustment of calcium concentrations. CONCLUSIONS: Albumin-adjusted calcium cannot be used in an intensive care setting to monitor reliably the calcium levels in critically ill patients and should be replaced by measurement of ionized calcium.     

Calcium and magnesium levels during automated plateletpheresis in normal donors

It is well known that citrate induces ionized hypocalcaemia by the chelating effect during plateletpheresis. However, the kinetics of serum magnesium (Mg) ions has not been well documented. We, therefore, evaluated biochemical changes in healthy donors during plateletpheresis procedure. Ten healthy donors underwent plateletpheresis on continuous cell separator (CS3000, Baxter, Round Lake, IL, USA) and 10 on intermittent flow cell separator (MCS 3p, Hemonetics, Braintree, MA, USA). Serum levels of total and ionized calcium (tCa and iCa, respectively) and Mg (tMg and iMg, respectively) were measured before, during and after the procedures. Although, the fall in tCa (from 2.62 +/- 0.12 to 2.36 +/- 0.12 mmol L(-1)) and tMg (from 0.89 +/- 0.01 to 0.79 +/- 0.01 mmol L(-1)) was modest and not significant; drop in iCa (from 1.33 +/- 0.1 to 0.84 +/- 0.1 mmol L(-1)) and iMg (from 0.53 +/- 0.01 to 0.35 +/- 0.1 mmol L(-1)) was statistically significant (P < 0.001). There were no significant differences observed between the CS3000 and MCS 3p cell separators regarding the fall in Ca and Mg. None of the donors experienced any adverse reactions during the procedures. In the study, an acute ionized hypocalcaemia and hypomagnesaemia have been observed after the plateletpheresis; therefore, measurement of both the ions may be monitored. However, there is no justification for prophylactic supplementation of either of these elements.     

Reversible hypocalciuria with marginal hypercalcaemia in renal magnesium wasting

Low urinary calcium levels and hypomagnesaemia were observedin three subjects with renal tubular abnormalities. The first,with severe hypomagnesaemia due to congenital renal magnesiumwasting, had mildly raised serum ionized calcium levels (134-1.36mmol/l). The other two, a brother and sister, had features ofBarter's syndrome with hypokalaemia, mild hypomagnesaemia andhyper-reninaemia with normal serum ionized calcium levels. Hypocalciuriawas seen in 24-h urine collections and in 2-hourly timed urinecollections. Magnesium loading with intramuscular MgSO₄ was used to raiseserum Mg to within the normal range. Tubular reabsorption ofMg (TMg) rose while TCa fell, with a rise in fractional excretionof ionized Ca and a small drop in serum ionized Ca. Serum parathyroidhormone levels rose or remained constant This pattern is consistent with a shared Ca/Mg reabsorptivepathway with a rise in TCa when TMg is low, returning to normalwhen TMg is raised by Mg loading. In one subject, this imbalancewas associated with marginal hypercalcaemia. The site for thispathway is likely to be the thick ascending limb of the loopof Henle.     

Development of ionized hypomagnesemia is associated with higher mortality rates

OBJECTIVE: Previous studies have shown a wide variation in the prevalence of total serum hypomagnesemia in intensive are unit (ICU) patients and in associated mortality rates. As the ionized part of magnesium is the active portion, we sought to define the prevalence of ionized hypomagnesemia in critically ill patients and to evaluate its relationship with organ dysfunction, length of stay, and mortality. DESIGN: Prospective observational study. SETTING: A 31-bed, medical-surgical, university hospital ICU. PATIENTS: A total of 446 consecutive patients admitted to the ICU over a 3-month period. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: The ionized magnesium level (normal value, 0.42-0.59 mmol/L) was measured at admission and then every day until discharge from the ICU. At admission, 18% of patients had ionized hypomagnesemia, 68% had normal ionized magnesium levels, and 14% had ionized hypermagnesemia. There was no significant difference in the length of stay or in the mortality rate between these three groups of patients. Hypomagnesemic patients more frequently had total and ionized hypocalcemia, hypokalemia, and hypoproteinemia. A total of 23 patients developed ionized hypomagnesemia during their ICU stay; these patients had higher Acute Physiology And Chronic Health Evaluation II (14.9 +/- 5.4 vs. 11.0 +/- 6.2) and Sequential Organ Failure Assessment (SOFA; 7.1 +/- 5.4 vs. 3.9 +/- 2.8) scores at admission (p <.01 for both), a higher maximum SOFA score during their ICU stay (10.0 +/- 5.6 vs. 4.4 +/- 3.2, p <.01), a higher prevalence of severe sepsis and septic shock (57 vs. 11%, p <.01), a longer ICU stay (15.4 +/- 15.5 vs. 2.8 +/- 4.7 days, p <.01), and a higher mortality rate (35% vs. 12%, p <.01) than the other patients. The major risk factors for developing hypomagnesemia during the ICU stay were a prolonged ICU stay, treatment with diuretics, and sepsis. CONCLUSION: Development of ionized hypomagnesemia during an ICU stay is associated with a worse prognosis. It is often associated with the use of diuretics and the development of sepsis. Monitoring of ionized magnesium levels may have prognostic, and perhaps therapeutic, implications.     

Ionized magnesium in erythrocytes--the best magnesium parameter to observe hypo- or hypermagnesemia

BACKGROUND: Almost 99% of the body magnesium is inside cells. The concentration of intracellular ionized magnesium (iMg) is physiologically relevant. iMg in erythrocytes is a new parameter that can help to establish reliable information on the functional magnesium status. METHODS: iMg concentration in erythrocytes and serum was measured by ion-selective electrode, in clinical analyzer Microlyte (KONE). Total magnesium (tMg) concentration was measured by atomic absorption spectrometry (AAS). Albumin and total protein concentration were measured colorimetrically. RESULTS: In critically ill postoperative patients, the mean of albumin, protein and hematocrit concentration was significantly lower compared to healthy individuals. Hypomagnesemia was found in 15.9% patients as tMgs, at 22.2% as iMgs and 36.5% as iMge. Significant correlations are between iMgs and tMgs or iMge and iMgs/tMgs. In dialyzed patients, the mean of hematocrit was significantly lower, iMge was significantly higher compared with healthy individuals. Significant negative correlations are between iMgs and tMge or iMge/tMge and tMge. CONCLUSIONS: iMge is the best magnesium parameter to observe hypo- or hypermagnesemia for both groups of patients. The function of magnesium is mainly intracellular and intracellular magnesium concentrations can be the method to evaluate the magnesium status.     

Ionized magnesium levels and the ratio of ionized calcium to magnesium in asthma patients before and after treatment with magnesium

OBJECTIVE: Prior studies have been equivocal about the efficacy of magnesium therapy in acute asthma exacerbations. We hypothesize that pretreatment ionized magnesium (Mg(2+)) levels and/or the ratio of ionized calcium to ionized magnesium (Ca(2+)/Mg(2+)) may have been confounding variables in these previous studies. Here, we report on the incidence of abnormal divalent ion levels in our asthma population. MATERIAL AND METHODS: The study was designed as a randomized, double-blind, placebo-controlled trial of intravenous magnesium. Inclusion criteria were: age >18 years, percentage predicted forced expiratory volume (FEV(1)) <75 % after an initial beta-agonist. African-American patients (AA) at an urban university hospital were randomized to 2 g IV Mg or placebo. Mg(2+) and Ca(2+)/Mg(2+) levels were measured pre- and post-infusion. Data were reported as means+/-SD. Student's t-test and Fisher's exact test were used where appropriate (alpha = 0.05, two tailed). RESULTS: Fifty-five AA patients (mean age of 42.7 years+/-15.6 years, range 18-75 years) were studied. A significantly (p<0.05) lower level of Mg(2+) was found in asthma (AS) patients compared with that in the AA group, by 0.03 mmol/L (95 % CI, 0.007-0.053 mmol/L). The AS group had a mean increase in Ca(2+)/Mg(2+) ratios over the AA group, of 0.27 (95 % CI, 0.16-0.38); 100 % of patients with abnormal divalent ion levels were corrected with IV magnesium. CONCLUSIONS: We identified a subgroup of asthmatic patients with significant abnormalities in their divalent ion concentrations, which was corrected with IV magnesium.     

危重患者高浓度静脉补钾的安全性和疗效研究

目的 探讨高浓度钾微量泵入治疗危重患者低钾血症的安全性及有效性.方法 128例合并低钾血症的危重患者[内生肌酐清除率(CCr)＞0.5 ml/s且每小时尿量＞50 ml]被随机分为治疗组和对照组,各64例.治疗组和对照组补钾浓度分别为1 208 mmol/L(相当于质量分数为9%的KCl溶液)、201 mmol/L(相当于1.5%的KCI溶液),补钾速度相同.均进行严密监测与血钾浓度监测,血钾正常时停止补钾.结果 治疗组和对照组补钾时间比较差异无统计学意义[(15.55±3.22)h比(14.18±4.93)h,P＞0.05];治疗组补钾的液体量明显低于对照组[(124.36±25.79)ml比(680.83±36.70)ml,P＜0.01].两组治疗过程中均未发生明显血流动力学变化、高钾血症或急性心功能不全.两组患者肾功能是否正常对补钾时间无明显影响.补钾前血钾浓度与补钾量有一定相关性(相关系数r=-0.259,P＜0.01).结论 高浓度钾微量泵入治疗危重患者低钾血症可以在短时间内纠正低钾血症,是安全有效的.肾功能轻度异常但无少尿及无尿的患者也可以在严密监测下高浓度补钾.     

Influence of blood sampling techniques on ionized magnesium level

The aim of the study was to evaluate whether different blood sampling techniques (venous vs. capillary) influence the level of ionized magnesium. A total of 12 men and 20 women were included. A venous blood sample was collected from the antecubital vein without stasis in syringes containing 50 IU/ml electrolyte balanced heparin. Capillary tubes containing sodium heparin 50 IU/ml were used for blood sampling (150 µl) from the earlobe. A statistically significant difference between venous and capillary ionized magnesium at actual pH (0.57 &#45 0.04 vs. 0.55 &#45 0.04 mmol/L, p<0.05) was observed, whereas no difference was seen between adjusted ionized magnesium. No difference was observed between venous and capillary ionized calcium at actual pH or adjusted to pH 7.4. The pH level was significantly higher in capillary blood (7.44 &#45 0.02 vs. 7.48 &#45 0.02, p<0.00001). The higher pH in capillary blood may be due to greater exposure to air in capillary tubes, and this most likely explains the observed difference between venous and capillary ionized magnesium at actual pH.     

Hemodynamic instability after the initiation of extracorporeal membrane oxygenation: role of ionized calcium

OBJECTIVES: To prospectively document the occurrence of ionized hypocalcemia in infants and children treated with extracorporeal membrane oxygenation (ECMO), to determine if the type of calcium salt (calcium chloride or gluconate) used in priming the ECMO circuit affected ionized calcium, to determine if ionized calcium concentrations correlate with total calcium, protein, albumin, or total magnesium values, and to determine if the hypotension usually observed after ECMO initiation correlates with low circulating ionized calcium concentrations. DESIGN: Prospective study. SETTING: Pediatric ICU and neonatal ICU. PATIENTS: Sixteen neonatal and three pediatric patients who were started on ECMO for cardiopulmonary support. INTERVENTIONS: The ECMO circuit was primed in a standardized manner, 100 mg of calcium gluconate was added in group 1 patients and 100 mg of calcium chloride was added in group 2 patients. MEASUREMENTS: Ionized calcium was measured from the circuit before initiation of ECMO and from the patient before, and then 5, 10, 15, 30, 60, 120, and 240 mins after initiation of ECMO. Total calcium and ionized calcium concentrations were measured simultaneously every 6 hrs. Serum total protein, albumin, magnesium, and ionized calcium values were measured from blood samples collected simultaneously twice daily. RESULTS: A significant decrease in the mean serum ionized calcium value occurred 5 mins after the initiation of ECMO in both groups, p less than .001. The ionized calcium value remained significantly decreased until 30 mins after the initiation of ECMO. There were no differences between the ionized calcium concentrations obtained during priming with calcium gluconate vs. those concentrations obtained with calcium chloride priming (p = .79). Throughout the course of ECMO, the serum ionized calcium concentrations ranged from 0.60 to 1.86 mmol/L. Poor correlations existed between circulating ionized calcium values and total calcium (r2 = .30), total protein (r2 = .20), albumin (r2 = .20), and magnesium concentrations (r2 = .10). There was a good correlation between the patients' BP and ionized calcium concentrations after bypass was initiated (r2 = .87). CONCLUSION: Our data demonstrate that ionized hypocalcemia is a frequent occurrence after the initiation of ECMO. Since there is a poor correlation between ionized calcium and total calcium, ionized calcium concentrations should be measured directly in these patients.     

Electrolyte abnormalities in critically ill children.

OBJECTIVE: To provide a brief overview of the causes, diagnosis, and therapies of electrolyte abnormalities frequently seen in critically ill children. DATA SOURCE: Published articles and bibliographies identified from pertinent review articles and books published in the past 20 yrs on fluid and electrolyte therapy in children. CONSTRAINT: The review includes only human studies and articles published in the English language. STUDY SELECTION: Human studies pertaining to abnormalities of water homeostasis, sodium, potassium, calcium, and magnesium homeostasis in children were selected. Prospective randomized studies were selected as much as possible. DATA EXTRACTION: Pertinent data abstracted from multiple, independent clinical studies were used to develop an approach to electrolyte abnormalities in critically ill children. DATA SYNTHESIS: An approach to diagnosis and therapies of common electrolyte abnormalities in critically ill children. CONCLUSIONS: Electrolyte abnormalities are common in critically ill children and can be easily treated once recognized. Further studies are needed to better understand the role of ionized calcium and magnesium in neonatal and pediatric critical illness.     

Intracellular and extracellular, ionized and total magnesium in pre-eclampsia and uncomplicated pregnancy.

Magnesium (Mg) and calcium (CA) concentrations in women with pre-eclampsia, women with an uncomplicated pregnancy and non-pregnant women were compared. Ionized serum magnesium and calcium concentrations and intracellular magnesium concentrations were measured in 15 pregnant women with severe pre-eclampsia, 34 uncomplicated pregnant women early, at midterm and preterm in their pregnancy and 24 non-pregnant women. The ionized calcium concentration did not chance during normal pregnancy or during pre-eclampsia relative to non-pregnant women. In contrast, elevated total and ionized magnesium serum concentrations were found in women with severe pre-eclampsia (total Mg = 0.85+/-0.11 mM, ionized Mg = 0.61+/-0.06 mM) relative to uncomplicated pregnant women (total Mg = 0.72+/-0.06 mM, ionized Mg = 0.53+/-0.03 mM). Total magnesium in pre-eclamptic women were similar to non-pregnant women. Intracellular ionized and total magnesium concentrations in mononuclear blood cells and erythrocytes were similar in pre-eclamptic women and women with uncomplicated pregnancy. Serum magnesium concentrations are elevated in severe pre-eclamptic women relative to women with uncomplicated pregnancy and are related to birth weight and gestational age at delivery. There may be a causal relationship since magnesium is involved in blood pressure regulation through an intracellular inhibition of NO synthase in endothelial cells.