Magnesium and open-heart surgery

Magnesium supplementation reduces postoperative arrhythmias after cardiopulmonary bypass in pediatrics: a metaanalysis of randomized controlled trials

Postoperative arrhythmia (POA) is the most common complication encountered after cardiopulmonary bypass (CPB). The preventive effect of magnesium in POA has been confirmed by metaanalyses in adults, but less is known in pediatric patients. A metaanalysis of published trials was conducted to examine the efficacy of magnesium supplementation in POA prevention among pediatric patients undergoing CPB. Relevant trials were identified from electronic databases (Medline, Embase, Web of Science, and Cochrane library). Pooled relative risk (RR) and 95 % confidence intervals (CI) were calculated using Mantel-Haenszel random-effects models, and heterogeneity was determined qualitatively according to I (2) and chi-squared statistical analyses. Among 121 potentially relevant studies, five randomized controlled trials met the inclusion criteria, resulting in a pooled total of 348 participants. Compared with placebo, magnesium supplementation decreased the incidence of arrhythmia after CPB in pediatric patients by 66 % (RR, 0.34; 95 % CI, 0.18-0.65; P = 0.001), with no heterogeneity between trials (heterogeneity P = 0.68; I (2) = 0 %). Magnesium supplementation significantly reduces the incidence of postoperative arrhythmias in pediatric patients undergoing CPB. Although the findings encourage the use of magnesium as an alternative to postoperative arrhythmias after CPB in pediatric patients, higher-quality randomized clinical trials are necessary before the findings can be generalized.

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.

Is low magnesium concentration a risk factor for coronary heart disease? The Atherosclerosis Risk in Communities (ARIC) Study

BACKGROUND

Hypomagnesemia has been hypothesized to play a role in coronary heart disease (CHD), but few prospective epidemiologic studies have been conducted.

METHODS AND RESULTS

We examined the relation of serum and dietary magnesium with CHD incidence in a sample of middle-aged adults (n=13,922 free of baseline CHD) from 4 US communities. Over 4 to 7 years of follow-up, 223 men and 96 women had CHD develop. After adjustment for sociodemographic characteristics, waist/hip ratio, smoking, alcohol consumption, sports participation, use of diuretics, fibrinogen, total and high-density lipoprotein cholesterol levels, triglyceride levels, and hormone replacement therapy, the relative risk of CHD across quartiles of serum magnesium was 1.00, 0.92, 0.48, and 0.44 (P for trend=0.009) among women and 1.00, 1.32, 0.95, and 0.73 (P for trend=0.07) among men. The adjusted relative risk of CHD for the highest versus the lowest quartile of dietary magnesium was 0.69 in men (95% confidence interval 0.45 to 1.05) and 1.32 in women (0.68 to 2.55).

CONCLUSIONS

These findings suggest that low magnesium concentration may contribute to the pathogenesis of coronary atherosclerosis or acute thrombosis.

Magnesium and the anaesthetist

Magnesium plays an important role as a cofactor in many of the body's critical functions and reactions. A deficiency or excess of extracellular magnesium can produce significant signs and symptoms. Hypomagnesaemia is a common finding in hospitalised patients, especially those in critical care areas. Anaesthetising hypomagnesaemic patients may exacerbate pre-existing cardiovascular disease and increase the risk of perioperative dysrhythmias. A low serum magnesium level usually suggests a total body deficiency of magnesium. Treatment of magnesium deficiency is by parenteral magnesium and should be instituted prior to surgery. Hypermagnesaemia is often iatrogenic and is more likely in patients with renal dysfunction who are receiving oral or parenteral magnesium. The specific antidote is intravenous calcium. Anaesthetised patients with high serum magnesium levels are at risk from hypotension, potentiation of non-depolarising neuromuscular blockers, postoperative respiratory failure and cardiac arrest.

Plasma magnesium during epidural anaesthesia. A study in patients undergoing transurethral prostatectomy

The variations of plasma magnesium concentration in relation to protein concentration and plasma volume were studied in 12 patients during epidural anaesthesia for transurethral prostatectomy. The most significant changes in plasma magnesium concentration were observed during the onset of anaesthesia. From the arrival in the operating theatre to the start of operation, the concentration of plasma magnesium decreased from 0.88 (SD 0.10) mmol/l to 0.82 (SD 0.10) mmol/l. At the same time, the increase of 16 per cent in plasma volume was associated with a rise of 8.4 per cent in the total amount of magnesium in plasma. After commencement of surgery, the plasma magnesium concentration was unchanged throughout the remainder of the study period. The total plasma protein concentration and the erythrocyte volume fraction decreased during the onset of anaesthesia, remained stable during surgery and returned to initial values one hour postoperatively. The pre-operative changes in the plasma magnesium concentration may have been the result of haemodilution and mobilisation of magnesium ion from its bone stores. Postoperatively, an increased urinary loss of magnesium must have followed the injection of frusemide at the end of surgery. The consequences of these variations in plasma magnesium concentration are unlikely to be of clinical significance, except in patients with pre-existing subclinical magnesium deficiency.