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Ionized magnesium concentrations in critically ill children
Insights
Many critically ill children have low ionized magnesium (IMg) levels, even with normal total magnesium (TMg) levels. Standard TMg tests may miss this critical deficiency in pediatric intensive care patients.
Area of Science:
- Pediatric Critical Care Medicine
- Clinical Chemistry
- Pediatric Endocrinology
Background:
- Critically ill children may present with electrolyte imbalances.
- Total magnesium (TMg) is routinely measured, but ionized magnesium (IMg) is the biologically active form.
- Normal TMg levels do not always exclude magnesium deficiency.
Purpose of the Study:
- To investigate the prevalence of ionized hypomagnesemia in critically ill children.
- To determine if ionized hypomagnesemia occurs despite normal total magnesium concentrations.
- To compare ionized magnesium levels in critically ill children with healthy children.
Main Methods:
- Prospective, observational study involving convenience sampling.
- Inclusion of critically ill children (1 day to 21 years) admitted to pediatric and cardiovascular intensive care units.
- Measurement of plasma ionized magnesium (IMg) and total magnesium (TMg) using a blood analyzer, with a comparison group of healthy children.
Main Results:
- 59% of critically ill children had ionized hypomagnesemia (IMg <0.40 mmol/L).
- Of those with hypomagnesemia, 60% had normal total magnesium concentrations.
- Critically ill children showed significantly lower IMg levels than healthy children (0.37±0.10 mmol/L vs. 0.46±0.03 mmol/L).
Conclusions:
- Ionized hypomagnesemia is common in critically ill children, often undetected by standard TMg tests.
- Routine TMg testing may fail to identify magnesium deficiency in this vulnerable population.
- Critically ill children have demonstrably lower ionized magnesium levels compared to healthy peers.
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.