Blood ionized magnesium concentrations during cardiopulmonary bypass and their correlation with other circulating cations

Systematic Review and Meta-Analysis to Estimate a Reference Range for Circulating Ionized Magnesium Concentrations in Adult Populations

BACKGROUND

There is a lack of consensus on a reference range for ionized magnesium (iMg2+) in blood as a measure of the status of circulating iMg2+ for the screening of populations.

OBJECTIVES

We estimated the reference range of iMg2+ levels for healthy adult populations and the ranges for populations with cardiovascular disease (CVD), type 2 diabetes, hypertension, and renal disease. We also estimated 95% ranges for circulating magnesium (Mg) in healthy and those with cardiometabolic diseases.

METHODS

We searched Ovid MEDLINE, Cochrane Central Register of Controlled Trials, and Embase through 24 July, 2020 to identify articles. We included English, peer-reviewed, randomized controlled trials, prospective and retrospective cohort studies, case-control studies, and cross-sectional studies that measured iMg2+ in blood or circulating Mg at baseline. The protocol was registered on PROSPERO (CRD42020216100). Estimated ranges were calculated by employing a frequentist random-effects model using extracted (or calculated) means and SDs from each included study. We determined the 95% confidence interval of the pooled mean.

RESULTS

A total of 95 articles were included with 53 studies having data for healthy participants and 42 studies having data for participants with cardiometabolic diseases. The estimated reference range for iMg2+ for healthy populations was 0.40-0.68 mmol/L, 0.38-0.64 mmol/L for CVD, 0.34-0.66 mmol/L for type 2 diabetes, 0.39-1.04 mmol/L for hypertension, and 0.40-0.76 mmol/L for renal disease. For circulating Mg, the estimated range was 0.72-1.0 mmol/L for healthy adults, 0.56-1.05 mmol/L for CVD, 0.58-1.14 mmol/L for type 2 diabetes, 0.60-1.08 mmol/L for hypertension, and 0.59-1.26 mmol/L for renal disease.

CONCLUSIONS

Estimated reference ranges for cardiometabolic disease states for both iMg2+ and circulating Mg were broad and overlapped with the estimated range for healthy populations (0.40-0.68 mmol/L). Further studies should evaluate whether iMg2+ can be used as a biomarker of cardiometabolic disease.

A Study of Hypomagnesemia in Patients Admitted to the ICU

Introduction After potassium, magnesium (Mg2+) is the most prevalent cation found intracellularly in the human body. The maintenance of excitability by Mg2+ and other cations is crucial for the neuromuscular junction to operate normally. Magnesium shortages are frequently overlooked compared to other electrolyte disorders such as hyponatremia, hypokalemia, and hypocalcemia. The present study aimed to study the factors and effects of hypomagnesemia among intensive care unit (ICU) patients who are critically ill at a tertiary care hospital. Methods This is a prospective observational study done among the patients who got admitted to the Medical ICU at Maharajahs Institute of Medical Sciences (MIMS), Nellimarla, Vizianagaram, from January 2020 to June 2021. A total of 100 patients were included in the study, of which 50 were cases and 50 were controls. The cases are those patients admitted to the medical ICU with critical illness and hypomagnesemia, and the controls are selected from those patients admitted with critical illness to the medical ICU with normal magnesium levels. Patients with severe infections, including sepsis, respiratory failure, cardiac failure, renal failure, cerebrovascular accidents (CVA), poisonings, and diabetic ketoacidosis (DKA), were included in the study. Patients who were treated with magnesium before admission to our ICU were excluded from this study. Serum magnesium was tested within 24 hours of admission and is correlated with the outcomes of the patients in terms of APACHE II score, length of ICU stay, and requirement and duration of ventilatory support. Results Out of a total of 50 cases, 29 (58%) are of males. The mean age of cases was 57.6 ∓ 8.2 years. Most cases were admitted due to organ failure (30%), followed by sepsis (26%) and poisoning (22%). The mean magnesium levels were 1.19 mg/dL among the cases, which was significantly lower when compared to the control group (2.16 mg/dL) (p-value= 0.01). The mean length of stay in the ICU was 6.12∓5.16 days in cases, whereas it was 5.28∓3.37 days in the control group (p-value = 0.33). 12% of cases needed non-invasive ventilation (NIV) when compared to 8% of controls (p-value= 0.50). 48% of the cases needed invasive ventilator support when compared to 28% in the control group (p-value= 0.03). The duration of invasive ventilation was higher among the cases (mean = 10 ∓3-17 days) compared to the controls (mean = 3 ∓2-4 days); p-value = 0.001. Mortality was higher in the case group at 28% (14) and was 10% (5) in the control group (p-value = 0.02). Conclusion The need for invasive ventilation and duration of invasive ventilation were significantly higher among the patients with hypomagnesemia compared to the patients with normal magnesium levels (p-value <0.05). Mortality was higher in the cases than in the controls (p-value <0.05).

The role of magnesium sulfate in the intensive care unit

Magnesium (Mg) has been developed as a drug with various clinical uses. Mg is a key cation in physiological processes, and the homeostasis of this cation is crucial for the normal function of body organs. Magnesium sulfate (MgSO4) is a mineral pharmaceutical preparation of magnesium that is used as a neuroprotective agent. One rationale for the frequent use of MgSO4 in critical care is the high incidence of hypomagnesaemia in intensive care unit (ICU) patients. Correction of hypomagnesaemia along with the neuroprotective properties of MgSO4 has generated a wide application for MgSO4 in ICU.

The relationship between ionized and total serum magnesium concentrations during abdominal surgery

STUDY OBJECTIVE

To determine the necessity for ionized magnesium (iMg) assay by evaluating the effect of abdominal surgery without massive transfusion on total magnesium (Mg) and iMg concentrations.

DESIGN

Prospective, observational study.

SETTING

Operating rooms at a university teaching hospital.

PATIENTS

31 patients without electrolyte abnormalities who were scheduled for abdominal surgery.

INTERVENTIONS

None.

MEASUREMENTS

Serum electrolytes, iMg, ionized calcium, proteins before and after surgery, and urine Mg were recorded.

MAIN RESULTS

Total Mg and iMg decreased: Mg 23%, iMg 15%; p < 0.0001. Total and iMg were highly correlated (r = 0.728, p < 0.0001). Urine Mg output remained within normal limits (mean 0.24 mmol/hr).

CONCLUSIONS

During abdominal surgery without massive transfusion, both total and ionized hypomagnesemia occur. Changes in iMg and total serum Mg concentrations are closely correlated. Total serum Mg assay, while overestimating the prevalence of ionized hypomagnesemia, is sufficient to screen for hypomagnesemia.

Influence of heart surgery on magnesium concentrations in pediatric patients

BACKGROUND

There have been only a few investigations into the effects of cardiopulmonary bypass (CPB) on the magnesium (Mg) concentrations in pediatric patients. The purpose of the present study was to compare the postoperative Mg concentrations and their recovery time to pre-surgical values in pediatric patients undergoing CPB for surgical repair of congenital heart disease. The incidence of dysrhythmia was also determined.

METHODS

Twenty-seven pediatric patients undergoing open-heart surgery with CPB were enrolled in this study. Controls were 23 pediatric patients undergoing palliative surgery without CPB. Serum Mg (SMg) concentrations and ionized Mg (iMg) concentrations were measured at four sample points: 24 h before the surgery, immediately after the surgery, 24 h after the surgery and 48 h after the surgery.

RESULTS

Serum Mg and iMg concentrations were significantly decreased after open-heart surgery. Immediately after the surgery, the mean SMg concentration was 64.1% and the mean iMg concentration was 68.8% of the pre-surgical values. The concentration of iMg showed quicker recovery than that of SMg, and returned to normal range 48 h after surgery. However, SMg and iMg concentrations after palliative surgery did not show significant differences from the pre-surgical values. The incidence of dysrhythmia was almost the same between the two groups; dysrhythmia was observed in two patients in the open-heart surgery group and in three patients in the palliative surgery group.

CONCLUSIONS

Mg concentrations showed significant decrease after CPB; however, they showed quick recovery and did not increase the incidence of dysrhythmia in pediatric patients.

Hypomagnesemic disorders

Adequate magnesium stores are vitally important for life. Critically ill patients will almost always have diminished levels of circulating magnesium, and this predisposes them to a variety of adverse effects, some life threatening. The causes of hypomagnesemia are many and varied, but in the critically ill, losses from the kidneys, often secondary to medications and from the gastrointestinal (GI) tract, predominate. The measurement of magnesium is not straightforward, although many clinicians are now switching to the use of ionized magnesium from ion selective electrodes. The use of supplemental magnesium in acute flares of asthma has some support in medical literature, especially for those patients with severe disease who fail traditional therapy. Magnesium holds the preeminent position in the treatment of pre-eclampsia and eclampsia in the minds of most obstetricians, who have decades of experience showing it to be both effective and safe. Magnesium is clearly useful for certain types of ventricular tachycardia, and probably assists in the treatment of several types of supraventricular tachycardia. Its role in acute myocardial ischemia is less certain, although there is no benefit once reperfusion therapy has already been carried out. Finally, the role of magnesium in the treatment of acute cerebral insults is an exciting area of active investigation with initial studies suggesting much promise.

Whole blood ionized magnesium: age-related differences in normal values and clinical implications of ionized hypomagnesemia in patients undergoing surgery for congenital cardiac disease

OBJECTIVES

We sought to (1) determine reference values for whole blood ionized magnesium concentrations in newborns, children, and young adults and (2) evaluate the frequency and clinical implications of ionized hypomagnesemia in patients undergoing surgery for congenital heart disease.

METHOD

We prospectively measured ionized magnesium concentrations in 299 subjects (113 control subjects and 186 patients undergoing surgery for congenital heart disease). Subjects were categorized by age. In the surgical group blood samples were obtained before bypass, during bypass (cooling and rewarming), after bypass, and during admission to the intensive care unit. Ionized hypomagnesemia was defined as ionized magnesium level 2 standard deviations below the mean of control subjects in the same age group. Patients were analyzed, controlling for cardiopulmonary bypass time.

RESULTS

In the control group ionized magnesium concentrations differed by age. Neonates and adults showed lower ionized magnesium concentrations compared with those of other age groups. Infants exhibited the highest ionized magnesium concentration. In the surgical group patients older than 1 month showed a higher proportion of ionized hypomagnesemia compared with that found in neonates at baseline (P <.001), after bypass (P =. 03), and at admission to the intensive care unit (P =.02). Controlling for cardiopulmonary bypass time, patients older than 1 month who were hypomagnesemic during bypass showed longer intubation time (P =.001) and longer intensive care stay (P =.01) and tended to have a higher pediatric severity of illness score on intensive care admission (P =.14) compared with patients without ionized hypomagnesemia.

CONCLUSIONS

There are age-related differences in normal ionized magnesium concentrations. Ionized hypomagnesemia is a common and clinically relevant occurrence among patients older than 1 month of age undergoing surgery for congenital heart disease.

Ionized magnesium concentrations in critically ill children

OBJECTIVE

To test the hypothesis that many critically ill children exhibit ionized hypomagnesemia despite having normal total magnesium (TMg) concentrations.

DESIGN

A prospective, observational study with convenience sampling.

SETTING

Pediatric and cardiovascular intensive care units of a large children's hospital.

PATIENTS

Patients aged 1 day to 21 yrs admitted from January 1 to October 31, 1996. Patients with chronic renal failure or weight <3 kg were excluded. A group of healthy children involved in a school-based nutritional assessment study were also studied.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Sixty-seven patients (5.4+/-5.7 [SD] yrs) and 24 healthy children (10.84+/-0.93 yrs, p< .001) were studied. Plasma was assayed for ionized magnesium (IMg) using a blood analyzer. Forty (59%)/67 critically ill subjects had IMg concentrations <0.40 mmol/L, the lowest published normal value and the lowest value observed in our group of healthy children. Of these, 24 (60%)/40 had normal TMg concentrations. IMg was significantly (p=.00) lower in critically ill subjects than in the group of healthy children (0.37+/-0.10 mmol/L vs. 0.46+/-0.03 mmol/L). IMg did not correlate strongly with ionized calcium (r2=0.49), albumin (r2=0.09), or pH (r2=0.18).

CONCLUSION

Many critically ill children exhibit ionized hypomagnesemia with normal TMg concentrations. These children would not be recognized as magnesium-deficient based on routine TMg testing. Critically ill children exhibited significantly lower concentrations of IMg than a group of healthy children.