Ultrafilterable hypomagnesemia in neonates admitted to the neonatal intensive care unit

To evaluate the frequency and clinical correlates of ultrafilterable hypomagnesemia in neonates admitted to the neonatal intensive care unit (ICU).

Prospective, observational study.

Massachusetts General Hospital and Mount Auburn Hospital.

A total of 117 patients (84 neonatal ICU patients and 33 normal newborns) studied over a 2-yr period of time.

Blood samples were collected during the first 48 hrs after admission. The concentrations of magnesium (total and ultrafilterable), ionized calcium, parathyroid hormone, electrolytes, glucose and arterial blood gases were determined.

Ultrafilterable circulating magnesium concentrations were determined in 74 of 84 neonatal ICU patients. On admission to the neonatal ICU, 23 (31.1%) of 74 neonates had ultrafilterable hypomagnesemia; two (2.7%) of 74 patients had ultrafilterable hypermagnesemia. Neonatal ICU patients had significantly lower (p < .001) ultrafilterable magnesium concentrations compared with normal neonates. Hypomagnesemic ICU patients required mechanical ventilatory support more frequently than did normomagnesemic ICU neonates (p < .05). Ionized hypocalcemia was a common finding in our patients (34 [42%] of 81). However, ultrafilterable hypomagnesemia was not statistically associated with ionized hypocalcemia (p > .05). Despite the below normal serum concentrations of ultrafilterable magnesium observed in our study, there was no impairment in parathyroid hormone secretion.

Ultrafilterable hypomagnesemia is a common finding in neonates admitted to the ICU. Ultrafilterable hypomagnesemia is associated with the need for mechanical ventilation. To our knowledge, this is the first report of ultrafilterable magnesium concentrations in normal and sick neonates.