Muscle and serum magnesium in pulmonary intensive care unit patients.
Level 4 - case-series / case-control
Case-control observational study comparing ICU patients to matched healthy controls
PubMed 3396369 · doi:10.1097/00003246-198808000-00004
What was done
Quadriceps femoris needle biopsies and blood samples were collected from 32 consecutive patients admitted to a pulmonary intensive care unit for chronic obstructive pulmonary disease and acute respiratory failure, alongside 30 age- and sex-matched healthy control subjects. Muscle magnesium and potassium contents were measured using atomic absorption spectrophotometry, and serum electrolytes were assessed alongside clinical outcomes.
What was found
Hypomagnesemia (serum magnesium 0.7 mmol/L or less) occurred in 3 of 32 patients (9.4%), all of whom had normal muscle magnesium. Low muscle magnesium occurred in 15 of 32 patients (47%), none of whom had abnormal serum magnesium levels. Muscle magnesium was significantly decreased in patients compared to controls. Serum magnesium did not correlate with muscle magnesium, nor did serum potassium correlate with muscle potassium. Muscle magnesium was significantly correlated with muscle and intracellular potassium. Patients with low muscle magnesium had lower muscle and intracellular potassium, a higher incidence of ventricular extrasystoles, and longer ICU stays. Exact effect sizes, means, and p-values were not provided in the abstract.
Why it matters
Serum magnesium levels do not reliably reflect intracellular magnesium deficits in critically ill pulmonary patients, meaning standard blood tests may overlook cellular depletion that tracks with potassium loss and ventricular arrhythmias.
Limits
Small sample size of 32 patients and 30 controls from a single center. The observational design cannot establish whether intracellular magnesium depletion caused longer ICU stays or arrhythmias. The abstract omits exact numerical concentrations and dispersion metrics. Routine muscle biopsy is invasive and impractical for standard clinical practice.
Cited by
- supports In one tissue biopsy study, 50% of people who were magnesium deficient showed normal blood magnesium levels.