The apparent impact of gestational magnesium (Mg) deficiency on the sudden infant death syndrome (SIDS)

Reports of studies in humans as well as data from several animal models show the importance of maternal dietary magnesium for the growth, development and survival of offspring. Published findings in mothers of victims of sudden infant death syndrome (SIDS) and in the SIDS victims are compared with characteristics of magnesium deficiency in humans and animals. Observations concerning the level of magnesium in traditional diets of selected ethnic groups with the highest or lowest rates of SIDS appear to confirm the importance of magnesium in protecting the offspring from sudden death. Ethnic groups with low SIDS rates at or below 1.2 per 1000 live births have rich dietary sources of magnesium, while those with SIDS rates exceeding 5.0 typically have magnesium-poor diets. Factors other than dietary magnesium are considered. Rat pups born and suckled by magnesium-sufficient dams have superior growth, development and survival, while those of deficient dams are feeble with impaired growth and development and have high perinatal mortality. In conclusion, these observations show that gestational magnesium deficiency results in suboptimal growth and development, with reduced survival of the offspring. Although the experimental data are compatible with a role for magnesium deficiency in SIDS, the cause of SIDS remains unknown and must be proved by appropriate biochemical analysis of tissue from SIDS infants compared with well-matched controls.

A triple-risk model for the sudden infant death syndrome (SIDS) and the apparent life-threatening episode (ALTE): the stressed magnesium deficient weanling rat

A triple risk model for the sudden infant death syndrome (SIDS) as described by Filiano and Kinney involves the intersection of three risks: (1) a vulnerable infant, (2) a critical developmental period in homeostatic control, and (3) an exogenous stressor(s). The triple risk model aptly describes the dynamics of an animal model for SIDS: (1) a vulnerable animal that is young and magnesium deficient: (2) a critical developmental period revealed by hyperirritability, labile cardiovascular and respiratory control; and (3) an exogenous stressor such as soft, high-pitched noise; motion or handling; or a chill. Together these three risks may trigger a shock-like episode of apnea, unconsciousness and bradycardia. The lung is the shock organ. An animal that dies quietly or after physical activity following the episode, models SIDS. However, if the shock-like episode resolves spontaneously or after resuscitation, the survivor is a model for an apparent life-threatening episode (ALTE). If, while still in the critical developmental period the ALTE survivor is stressed again, there is a risk for a recurrent episode, with the final outcome still unpredictable but with increasing risk for SIDS with multiple recurrences. The purpose of this communication is to present an illustrated review of the magnesium deficient weanling rat as an animal model for SIDS/ALTE, showing pertinent physical, electrocardiographic and pathological features. In the weanling rat, magnesium deficiency appears to be the single common pathway upon which multiple stressors may impinge to produce sudden death during the relatively brief critical developmental period, while magnesium supplements may protect the animal. If significant magnesium deficiency is subsequently diagnosed in a properly controlled study of human SIDS tissue, it is likely that a high proportion of SIDS deaths could be prevented by simple oral magnesium supplementation to infants during the first critical weeks and months of life.

Magnesium deficiency promotes muscle weakness, contributing to the risk of sudden infant death (SIDS) in infants sleeping prone

A review was published (1991) of 19 retrospective case-control studies that had investigated the relationship between prone sleeping position (on the stomach) and the sudden infant death syndrome (SIDS). These studies, which had been conducted between 1965 and 1990 in New Zealand, Australia, England, France and the Netherlands, showed an overall higher rate of SIDS in infants who usually slept prone. In those countries, vigorous community intervention to change babies' sleep position away from the prone has resulted in marked declines of 50 per cent or more in the rate of SIDS. Such encouraging reports from many countries prompted the American Academy of Pediatrics to recommend that infants be placed to sleep on their backs to reduce the risk of SIDS. This was followed by a successful campaign in the United States between mid-1994 and 1998. Despite the decreased incidence, SIDS remains the leading cause of death in infants 1 month to 1 year of age of industrialized nations of the world. Studies have been conducted in human infants, mechanical models and animal models to learn the role of risk factors in prone sleeping infants. Soft bedding, thermal stress and biologic risk factors such as impaired ventilatory and arousal responsiveness are among many factors that have been investigated. Hunt states that there is not a single unifying factor that explains increased SIDS in prone sleeping infants. Two major studies conducted in the 1970s showed: (1) muscle weakness in the upper half of the body in infants who subsequently died of SIDS, and (2) shoulder hypotonia in near-miss for SIDS infants. An infant sleeping face-down in the prone position could be jeopardized if he lacked the muscle strength to shift his position or turn his head to rescue himself from a life-threatening situation. In contrast, recent studies in neonates sleeping in the prone position report that normal infants can spontaneously arouse and turn their heads. Some data support the hypothesis that magnesium deficiency contributes to SIDS. Muscle strength is seriously impaired in the young magnesium deficient subject, while magnesium rapidly reverses muscle weakness. In rats, marginal deprivation in dietary magnesium reduces exercise capacity, an early effect of magnesium deficiency which is preventable by consuming magnesium-enriched mineral water. It is concluded that magnesium deficiency is at least one major unifying factor that explains increased SIDS in prone sleeping infants.

A review of the status of magnesium and related minerals in the sudden infant death syndrome (SIDS)

Sudden infant death syndrome (SIDS) is the sudden death of an infant under 1 year of age that remains unexplained after a thorough case investigation, including performance of a complete autopsy. Despite recent reductions in the SIDS rate attributed to placing the baby to sleep on his back, SIDS remains the most common cause of infant mortality between 1 month and 1 year of age in developed countries. This review concerns the current state of a hypothesis (1972) that magnesium deficiency, which causes sudden death in young mammals, is the major cause of SIDS. Numerous investigators have compared the concentration of magnesium, and other minerals from soft tissues and bone in SIDS with non-SIDS controls (normal infants who died suddenly of known cause such as trauma). Because of rapid shifts of minerals during early development, SIDS and control infants must be matched for gestational and postnatal age. About 95 per cent of SIDS occurs between 1-6 months of life, with peak incidence at 2-4 months, when vitreous magnesium is high. There is little change in magnesium in the relatively inert vitreous despite extremes in dietary magnesium. All values fall within a small range, with scatter. Magnesium rapidly increases in foetal cartilage with ossification of the bone. Early in magnesium deficiency, liver magnesium may be increased or unchanged, but it does not increase during magnesium excess. Lead accumulation is increased in magnesium deficiency. Among infants with high environmental exposure to lead, those who die of SIDS rather than non-SIDS infants have the greater lead burden. Soft water with low magnesium and calcium and with high concentration of sodium have been linked to higher SIDS rates, which have been attributed to low magnesium. It is concluded that the SIDS hypothesis has neither been proved nor disproved.

The possible role of magnesium in protection of premature infants from neurological syndromes and visual impairments and a review of survival of magnesium-exposed premature infants

The survival rate of very preterm, low birth weight infants (weighing less than 1500 g) is 85 per cent in the USA and is ever increasing, while 42 to 75 per cent of extremely premature infants (weighing 751-1000 g) survive. Of great concern is the lack of consistent decrease in neurological syndromes and associated visual impairments. Because of short gestations, these infants have not had time to accrue up to 80 per cent of magnesium normally present at term. These very preterm infants are at highest risk for cerebral hypoxia/ischemia (H/I), intracranial hemorrhage (ICH), periventricular leukomalacia (PVL) or cystic PVL (CPVL), and possible sequelae, cerebral palsy (CP) and mental retardation (MR). These syndromes are associated with damage to optic structures and the visual pathways which traverse the brain. Visual defects are common in surviving preterm infants. Increased levels of harmful neurochemical mediators that have been reported in these conditions include oxygen free radicals, excitatory amino acids, tumor necrosis factor-alpha (TNF-a), and thromboxane A2 (TXA2) which are aggravated in magnesium deficiency and may be ameliorated by magnesium. We review the published data concerning the effects of prenatal magnesium supplementation on ICH, CPVL, CP and MR and available reports concerning survival. Further considerations on the safety and efficacy of magnesium sulphate administration given prenatally to the preterm neonate await the outcome of three trials that are continuing for more than a year on three continents.

Evidence for magnesium deficiency in the pathogenesis of bronchopulmonary dysplasia (BPD)

Bronchopulmonary dysplasia (BPD) has been defined as a requirement for oxygen for more than 28 days because of chronic pulmonary changes, usually in a premature infant. About 50 per cent of very low birth weight (VLBW) infants who weigh 1 kg at birth and who survive 28 days will develop BPD. Since 80 per cent of fetal accretion of magnesium occurs during the third trimester, this population is also at risk for magnesium deficiency. This paper reviews evidence for a role of magnesium deficiency in the pathogenesis of BPD. Pathology in BPD that may be caused or aggravated by magnesium deficiency is noted. Agents or mediators that are increased in BPD and in BPD include: oxygen free radicals; the inflammatory cytokines interleukin (IL)-1 and IL-6, and tumour necrosis factor-alpha; vaso- and bronchoconstrictors thromboxane A2 (TXA2) and serotonin: vasoconstrictor, endothelin-1 (ET-1); and bronchoconstrictor, histamine. Magnesium deficiency increases the susceptibility of cells and tissues to peroxidation, worsens the inflammatory reaction, reduces the immune response, exaggerates catecholamine release in stress, and diminishes energy metabolism. Possibly because of the danger of magnesium toxicity and the difficulty in studying the preterm VLBW neonate, little is known about magnesium supplementation in this group. Such information must be gained through controlled studies on the effect of antepartum exposure to maternally administered magnesium sulphate on the VLBW infant, through carefully monitored postnatal administration of magnesium in an intensive care setting, or through evaluations of combined pre- and postnatal supplementation.

A review of evidence for a role of magnesium and possibly copper deficiency in necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a neonatal disorder of unknown cause characterized by rapid necrosis of the bowel, primarily the ileum and colon. It is a worldwide problem. NEC is the most common gastrointestinal emergency in the neonatal intensive care unit, and ranks second as a cause of neonatal death. The incidence of NEC is inversely proportional to the birth weight and the degree of maturity. Infants born at or before 28 weeks gestational age have not received 80 per cent of the magnesium and 67 per cent of the copper found at term. Congenital deficiencies of these essential minerals may be compounded by high renal or gastrointestinal losses and high metabolic demand during the preterm infant's accelerated growth. Platelet thrombi appear early in the intestinal microvasculature in NEC. Platelet thrombosis and release of vasoconstrictor, platelet aggregating thromboxane A2 (TXA2) in human NEC appears to potentiate the intestinal ischaemia and necrosis in neonates who develop NEC. Magnesium and copper deficiency each enhance the synthesis of TXA2. Plasma levels of the inflammatory cytokines tumour necrosis factor (TNF) and interleukin-6 (IL-6) are increased in NEC and in magnesium deficiency; these experimentally produce shock and tissue injury, especially of the intestine. The synthesis of the potent vasoconstrictor endothelin is increased in magnesium deficiency. NEC has been regarded as a luminal insult that causes local generation of destructive oxygen free radicals. Tissues from animals deficient in magnesium are more susceptible to oxidative injury and lipid peroxidation than tissues from normal animals. Magnesium and copper deficiency impair antioxidant defence through decreased synthesis of glutathione and reduced activity of Cu/Zn superoxide dismutase, respectively. Although the aetiology of NEC is unknown, there appears to be sufficient data to implicate magnesium and possibly copper deficiencies in the pathogenesis. Consequences of deficiency of one or both minerals may include increased synthesis or activity of injurious mediators: IL-1, IL-6, TNF, TXA2, endothelin, and oxygen free radicals. A prospective trial of magnesium supplementation, but not copper supplementation, in very premature neonates can be recommended, with NEC as one of the outcome measures.

Hypothesis: the possible role of magnesium and copper deficiency in retinopathy of prematurity

This hypothesis states that magnesium and copper (Cu) deficiency as well as high arterial oxygen pressure may contribute to the pathogenesis of retinopathy of prematurity (ROP), a major cause of blindness in very low birthweight preterm infants. Infants at highest risk have severe respiratory distress with hypoxia and require prolonged oxygen supplements. The retina is a multilayer sheet of neural tissue very rich in polyunsaturated fatty acids (PUFAs), oxygen, and mitochondria, with the highest oxygen consumption of all body tissues. Oxygen free radicals which are generated during metabolism cause lipid peroxidation of the PUFA-rich membranes, impairing retinal function. Magnesium and copper deficiencies provide less protection from oxidative injury which damages neurosensory tissue critical for photodetection. Protective antioxidant enzyme activity is reduced in magnesium and copper deficiency. There is some evidence for a raised level of vasoconstrictor thromboxane A2 (TXA2) in respect to vasodilator prostacyclin (PGI2), which would promote vasoconstriction. Deficiency of magnesium and of copper increase synthesis of TXA2 and decreases synthesis of PGI2. Sustained vasoconstriction leads to vascular occlusion, retinal ischaemia, reactive proliferation of retinal vasculature, and the final stages of ROP. Abundant magnesium and copper may protect the retina from developing ROP.

Hypothesis: possible links between the respiratory distress syndrome of the premature neonate, the sudden infant death syndrome, and magnesium deficiency shock

This hypothesis notes the similarities in the respiratory distress syndrome (RDS) of premature neonates, sudden infant death syndrome (SIDS) of postneonates, and the seizure-shock syndrome of acute magnesium (Mg) deficiency in stressed weanling animals, and suggests a common pathogenic link between the three. In each of these syndromes the lung is the major target organ, with haemorrhage, oedema, and microvascular congestion. It is suggested that platelet aggregation, leading to the transient release of mediators of shock, causes an acute, self-limited arachidonic acid cascade. The result of the shock is early death or spontaneous recovery with a propensity for recurrence; premature neonates who have had RDS are at particularly high risk for SIDS. Cases linking RDS and SIDS are cited.

Hypothesis: new concepts concerning the pathophysiology of the sudden infant death syndrome due to magnesium deficiency shock

There appear to be many contributing factors to sudden infant death syndrome (SIDS). One final common pathway that may explain some cases of SIDS is presented as a hypothesis: SIDS occurs as a shock-like event in a stressed infant with congenital or acquired magnesium deficiency with respect to calcium, or with genetically determined high magnesium requirements. Increased calcium and stress-related catecholamines favour platelet aggregation and release of mediators, chief of which appears to be thromboxane A2 (TXA2). TXA2, a major vasoconstrictor, bronchoconstrictor, and platelet aggregator is relatively unopposed during shock by prostacyclin, a vasodilator, bronchodilator, and platelet disaggregator which normally counterbalances its effects. The shock episode is self-limited. Infants who recover have suffered an apparent life threatening event (ALTE); those who die have insufficient pathology to explain the cause of death; the diagnosis is SIDS.

Magnesium therapy in premature neonates with apnea neonatorum

Apnea, bradycardia, and neuromuscular hyperirritability have been associated with magnesium (Mg) deficiency in young human infants and weanling animals. This is a retrospective review of a clinical experience of Mg therapy among 200 premature neonates who showed physical and clinical chemical changes compatible with Mg deficiency. The 200 infants all had idiopathic apnea neonatorum, and 93% also had the respiratory distress syndrome (RDS). This review was conducted to learn whether Mg therapy was associated with a significant reduction in apnea. The author suggested that the dose of Mg be 0.4 mEq/kg body weight/day, as 50% MgSO4.7H2O intramuscularly (IM) for 5 days; or as 1.0 mEq/kg/day, as 10% MgCl2.6H2O by mouth for 2 or more weeks, with appropriate monitoring of plasma Mg values in all infants. Sixty-one infants received a minimum of 5 days of Mg by either route (mean, 11.4 +/- 0.9, Group A); five received 3-4 doses IM (mean, 3.6 +/- 0.2, Group B); and 134 received 0-2 doses IM (0.5 +/- 0.1, Group C). Group A infants Mg-treated before Day 20 showed earlier cessation of apnea and bradycardia than those treated after Day 20. In Group A patients, 7 dose-days [corrected] of Mg therapy was associated with continuation of apnea; 14 dose-days [corrected], with cessation of apnea. Compared with Group A, Group C continued to develop apnea (P less than .003) and bradycardia (P less than 0.03) over longer periods of time. Group A infants showed no record of death or of hospital readmission for recurrent apnea, while 32 of 134 Group C infants had one or both of those unfavorable outcomes (P less than 0.001), with four of the five deaths in Group C (NS) as the sudden infant death syndrome (SIDS). In conclusion, Mg was associated with a reduction of apnea in this population. Emphasis was placed on the need to closely observe infants receiving supplementary Mg, with monitoring of plasma Mg levels.

Pulmonary lesion induced by stress in magnesium-deficient rats. A light- and electron-microscopic study

A light- and electron-microscopic study was made of the lungs of magnesium (Mg)-sufficient and Mg-deficient pathogen-free weanling rats raised in a gnotobiotic environment. Mg-sufficient rats were studied unstressed, after mild auditory stress, or after strychnine seizures and showed essentially no pulmonary pathology. Mg-deficient rats were studied with no known seizures or immediately after audiogenic seizure-shock. Light microscopy of lung from Mg-deficient rats with audiogenic seizure-shock revealed atelectasis, generalized edema and hemorrhage, and pleural petechiae. Ultrastructural changes in lung alveoli of Mg-deficient rats with seizure-shock included gaps in capillary endothelium, swelling and separation of endothelial cells from the underlying basement membranes; Type I cell necrosis and separation from basement membranes; and intraalveolar red blood cells, fibrin, and precipitated plasma. The seizure-shock episode of acute Mg deficiency produces structural changes in the lung similar to changes produced by several forms of shock, early acute oxygen toxicity, and the respiratory distress syndrome (RDS) in human neonates.

Protection by magnesium of renal calcinosis in furosemide-treated weanling rats with moderate magnesium deficiency

Prolonged treatment of premature infants with the potent diuretic furosemide has resulted in hypercalciuria, sometimes with renal calcinosis and other complications. Furosemide was administered to weanling rats to explore its effect on magnesium and calcium metabolism. The animals were fed purified diets providing 40 mg magnesium/100 g diet or 10 mg magnesium/100 g. Half of each dietary group (40-F or 10-F) received 18 doses of furosemide, 20 mg/kg body weight, intraperitoneally between days 7 and 35, and half received normal saline intraperitoneally (40-O or 10-O). Furosemide had little effect on the magnesium-sufficient animals (40-F), but comparison of 10-O and 10-F data showed that it aggravated the magnesium-deficiency syndrome. Comparison of data from 40-F and 10-F animals showed the protective effect of magnesium in preserving calcium homeostasis in furosemide-treated animals: the elevation of calcium values in 10-F rats was greater in plasma (p less than 0.0005), heart (p less than 0.0025), and kidney (p less than 0.0005). Stated another way, furosemide was associated with severely disordered calcium metabolism only in animals fed suboptimal magnesium. Studies exploring the role of magnesium in furosemide-treated infants can be recommended.

An evaluation of the parenteral magnesium load test in weanling rats

The parenteral magnesium (Mg) load test has reliably identified rats fed two extremes of dietary Mg, but tests of intermediate levels have not been found. The present study was designed to learn: 1) whether the parenteral Mg load test reflects a series of different dietary levels of Mg, rather than just the extremes; 2) what relationship exists between Mg retention and Mg in plasma and in bone at the different dietary levels of Mg; and 3) how the different dietary levels of Mg affect weight gain. Weanling rats were fed six levels of dietary Mg ranging from 0 to 150 mg/100 g purified diet. A negative relationship was found between retention of the Mg load and the level of dietary Mg. Mg retention decreased linearly with increases in plasma Mg and bone Mg. Weight gain was an insensitive index of dietary Mg. The parenteral Mg load test appears to be an acceptable means of indirectly assessing Mg stores in weanling rats with normal renal and cardiovascular status and normal water balance.

Parenteral magnesium load testing with 28Mg in weanling and young adult rats

A sound diagnostic test for Mg deficiency is needed. This is a report of the parenteral Mg load test conducted in weanling and young adult rats fed a purified basal diet containing 3 mg magnesium/100 g with 150 mg of added magnesium/100 g (control) or 0 added magnesium (deficient). Weanlings were studied at about 1 week of dietary treatment and young adults at 2 weeks. The protocol included: a) a 6-hour preload urinary collection; b) an intraperitoneal load of 15 mg of magnesium/kg (weanlings) or 12 mg/kg (young adults) with 2 microCi 28Mg given simultaneously with each load; c) a 6-hour postload urinary collection; d) chemical analysis of selected tissues and urine for Mg; and e) 28Mg counting 6 and 24 hours postload. Controls all excreted large amounts of Mg pre- and postload, retaining less than 26% of nonradioactive loads. They had high urinary 28Mg counts. In Mg-deficient animals, the concentration of Mg in bone more than halved. These animals avidly conserved Mg and retained over 85% of nonradioactive Mg loads. Their 28Mg activity in vital organs was 3--6 times greater than in controls. We concluded that the parenteral Mg load test reliably identifies severe Mg deficiency.

The postmortem diagnosis of magnesium deficiency: studies in an animal model for the human infant

Weanling rats were studied as a model for the human infant to determine the optimal tissue in which to assess the status of magnesium after death. Control rats were fed laboratory chow or purified diets that provided a surfeit of magnesium and accommodated a normal rate of growth. Other rats were fed diets that resulted in two degrees of magnesium deficiency: one that might result in spontaneous death within one week, and the other, within two weeks. These times may correlate with six months and one year in the human infant, the period during which the sudden infant death syndrome usually occurs. There was no consistent difference between the magnesium concentration found in the vitreous humor, liver, heart, or skeletal muscle of magnesium-deficient and control rats. However, bone accurately reflected the level of dietary magnesium. There was a significant difference between the magnesium concentration of the anterior and posterior halves of the ribs, indicating irregular distribution of magnesium within the bone. Significant differences were found in the magnesium concentrations of different bones from the same animals. Therefore one entire bone, such as the sternum or the rib, should be studied. The need to match control and study subjects for age was apparent.

Parenteral magnesium load tests in postpartum American women

The magnesium status of 185 moderate income American mothers was assessed in the immediate postpartum period by the intravenous magnesium load test. Pre- and postload collections of urine were each made for approximately 24 hours because pilot studies revealed significant diurnal variation in magnesium excretion. The magnesium load provided 0.4 to 0.5 mEq of magnesium/kg of estimated lean body weight. The mean retention was 51% +/- 2.2 (SEM). Patients retaining more or less than an arbitrary limit of 40% of the magnesium load were compared. No differences in mean age, weight, or parity were found between the groups. The high retention group reported a diet lower in magnesium and had a significantly lower plasma magnesium value. Magnesium retention of over 90% of the load was found in biologically immature multiparas (less than 17 years) and in young mothers of twins. Among the multiparous patients, those with the longest interval since the previous pregnancy had the lowest retention values. Most of the primiparous patients had met the magnesium requirements of a singleton pregnancy and rejected most of the load, but 6 primiparous women whose active labor exceeded 18 hours had a retention of 77.91% of the load. This was significantly higher than the 45.0 +/- 3.52 (SEM) % retention in 70 primiparous mothers with shorter duration of active labor (P less than 0.005). No other symptoms or complications of pregnancy could be correlated with the magnesium load values. Further definition of the magnesium load test is indicated.

The magnesium load test: III. correlation of clinical and laboratory data in infants from one to six months of age

A study of 64 infants from one to six months of age was made using the 32-hour parenteral magnesium load test. Most of the infants were studied for neuromuscular hyperirritability or other signs compatible with magnesium deficiency; some with unrelated problems served as controls. Magnesium retention below 40 per cent was found in 26 infants who presented with minor sign or signs that were otherwise explained, as by infection. Twelve who retained 72 per cent of the load were normal or small at birth, amply fed on demand, and grew at accelerated rates, increasing from the 50th to the 88th mean percentile by ten weeks, when they were "fat, hungry, jumpy babies," exemplifying the Mg deficiency syndrome of growth. Seven infants of 8.2 plus or minus 1 weeks had had one or more sudden, transient episodes that included: apnea, gasping, tonic or tonic-clonic fits, and flaccidity, often with pallor, cyanosis, eye signs, sweating, or tearing. Despite preload Mg in two, the group retained 88 per cent of the load. Mg appeared to be specific therapy in high retention groups. The signs are nonspecific but resemble premonitory signs and the type of episode that may occur in the sudden infant death syndrome (SIDS), suggesting a possible link between magnesium depletion and SIDS.

The magnesium load test: II. Correlation of clinical and laboratory data in neonates

Parenteral magnesium load tests were conducted on 91 infants less than one month of age, most of whom had marked hyperirritability and symptoms compatible with the diagnosis of electrolyte imbalance with relative or absolute magnesium deficiency. Most of the patients studied had a 40-hour test, with an eight-hour preload and a 32-hour postload collection of urine. Of 43 premature infants studied, only three retained less than 40 per cent of the load: one was untreated, one had low retention of a second load following a course of therapy, and the mother of the third had received magnesium within 24 hours of delivery. Of 48 full-term infants studied, ten retained less than 40 per cent of the load. These were asymptomatic or had minor problems. Irritability was common in both high and low retention groups. Ten per cent of the low retention group and 50 per cent of the high retention group manifested two or more of the nonspecific signs compatible with the diagnosis of magnesium deficiency; the difference was significant (P smaller than 0.025). Eleven premature and six full-term infants with very high initial retention received five or six intramuscular injections of magnesium, after which the magnesium retention was about 30 per cent lower than the initial value. For most patients, repletion therapy was given orally. Although low plasma magnesium values related to high magnesium retention, correlation on an individual basis was poor. The plasma calcium levels of three patients with combined hypomagnesmia and hypocalcemia failed to respond to calcium therapy and remained low until the plasma magnesium value was corrected. Magnesium appeared to be specific therapy for symptomatic infants found to be deficient. More males than females had sufficient symptoms to warrant study.

The magnesium load test: I. A design for infants

The purpose of this study was to design the shortest suitable magnesium load test for infants up to six months of age. A 56-hour test was used to study cation and creatinine excretion before and after an intramuscular load of 0.49 mEq of magnesium/kg of body weight. No diurnal excretion pattern for magnesium was found, and most of the magnesium rejected by the kidney was excreted by neonates within 32 hours, and by infants from one to six months of age within 24 hours. The postload urinary magnesium value usually stabilized at a slightlyhigher level than the preload level. The mean plasma magnesium level increased about 0.65 mEq/liter one hour after the load, and at the end of the test was 0.25 mEq/liter higher than the initial value; abnormally low plasma values were normalized. Renal excretion of creatinine and potassium was not affected by the magnesium load, but the 24-hour postload excretion was higher than the 24-hour preload excretion of calcium for all patients, and of sodium for some full-term neonates. Because of slow excretion of magnesium and concomitant caocium loss, special precautions are required for testing and repletion of young infants to avoid magnesium overload and calcium depletion. A suitable test would have an eight-hour preload period, a load of 0.49 mEq of magnesium (0.12 ml of 50 per cent MgSO4.7H20) per kg of body weight, and a postload collection of 32 hours for neonates and 24 hours for infants from one to six months of age.

Acquired heart disease in Ugandan children

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