Hypomagnesemia in Patients in Postoperative Intensive Care

doi:10.1378/chest.95.2.391

Chest

Volume 95, Issue 2, February 1989, Pages 391-397

https://doi.org/10.1378/chest.95.2.391 Get rights and content

In order to study the clinical consequences of postoperative hypomagnesemia, the serum magnesium (Mg) concentration was measured in samples of blood collected from 193 patients admitted to two postoperative ICUs. On admission to the ICU, 117 patients (61 percent) had hypomagnesemia (serum Mg <1.5 mEq/dl), 66 patients (34 percent) had normomagnesemia (1.5 to 2.0 mEq/dl), and ten patients (5 percent) had hypermagnesemia (>2.0 mEq/dl). There were no correlations between the severity of illness score (r = 0.145) or the degree of hypoproteinemia (r = 0.01) and the postoperative serum Mg level. Patients with sever hypomagnesemia (serum Mg ≤1.0 mEq/dl) experienced hypokalemia more often (p <0.02) than the others in the study. Furthermore, those with severe hypomagnesemia had a higher mortality rate (7/17 or 41 percent) than the remainder of the population studied (22/176 or 13 percent) (p<0.02). Those with severe hypomagnesemia had received aminoglycosides more often (p<0.001) than those with normal serum Mg concentrations. The serum Mg level was not a sensitive (68 percent) or specific (37 percent) predictor of survival. Our conclusions were as follows: (1) hypomagnesemia is common in postoperative ICU patients; and (2) patients in the postoperative ICU who have severe hypomagnesemia have a higher mortality and more hypokalemia than similarly ill patients with normomagnesemia. Because of the association between aminoglycoside therapy and severe hypomagnesemia, we recommend measurement of this variable in those patients receiving aminoglycosides. Furthermore, Mg replacement therapy is recommended for those patients with serum Mg values of 1 mEq/dl or less.

(Chest 1989; 95:391-97)

Section snippets

Subjects

One hundred and ninety-three patients admitted after surgery to the Respiratory-Surgical ICU or Gray Acute Care Unit of Massachusetts General Hospital were studied. All patients had undergone major abdominal, thoracic, or vascular procedures (Table 1). None of the patients was known to have hypomagnesemia or hypermagnesemia before surgery.

Design of Study

The following protocol was approved by the Subcommittee on Human Studies (the Institutional Review Board) at Massachusetts General Hospital: demographic data

RESULTS

Of the 193 patients studied on admission to the ICU, 117 (61 percent) had hypomagnesemia, 66 (34 percent) had normomagnesemia, and ten (5 percent) had hypermagnesemia. The mean ages (±SD) of the patients in the three groups were similar: 57.6 ± 16.4 years, 62.0 ± 15.4 years, and 55.5 ±21.7 years, respectively. The mean serum Mg concentration on admission to the ICU was 1.19 ±0.17 mEq/dl (range, 0.4 to 1.4 mEq/dl, 1.62±0.13 mEq/dl (range, 1.5 to 2.0 mEq/dl), and 2.41 ±0.35 mEq/dl (range, 2.1 to

Frequency of the Problem

The high prevalence of hypomagnesemia observed in the present study parallels the rate reported by Ryzen et al³ in their study of 94 patients in a medical ICU. Whang et al¹^,⁵^-⁷^,¹³ have performed extensive studies on this topic area and have reported incidences of 6.9 percent and 5.6 percent for hypomagnesemia and hypermagnesemia, respectively, in 2,300 hospitalized (non-ICU and ICU) patients.¹³ The frequency of hypermagnesemia which we observed in our surgical patients in the ICU (5 percent)

SUMMARY

Information about the hormonal¹¹ and metabolic⁴⁵^,⁴⁶ responses to surgery and surgically related problems is accumulating. This type of information has led to the development of novel approaches to the provision of metabolic support,⁴⁷ including the use of Mg salts⁴⁸^,⁴⁹ and even growth hormone.⁵⁰ Increasing evidence²⁹^,³⁰ supports the concept that Mg deficiency may cause arrhythmias, which is an important postoperative problem. Hypomagnesemia is a metabolic problem that may have important

ACKNOWLEDGMENT

We thank those members of the surgical staff of Massachusetts General Hospital who allowed their patients to participate in this study, Ms. Donia Goss for manuscript preparation, and the ICU nursing staff for their cooperation.

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Magnesium (Mg²⁺), also known as “the forgotten ion,” is the second most abundant intracellular cation and is essential in a broad range of intracellular physiological and biochemical reactions. Its deficiency, hypomagnesemia (Mg²⁺ < 1.8 mg/dL), is a prevalent condition and routinely poses challenges in its management in clinical practice. Sodium/glucose cotransporter 2 (SGLT2) inhibitors have emerged as a new class of drugs with treating hypomagnesemia as their unique extraglycemic benefit. The beneficial effect of SGLT2 inhibitors on magnesium balance in patients with diabetes with or without hypomagnesemia has been noted as a class effect in recent meta-analysis data from randomized clinical trials. Some reports have demonstrated their role in treating refractory hypomagnesemia in patients with or without diabetes. Moreover, studies on animal models have attempted to illustrate the effect of SGLT2 inhibitors on Mg²⁺ homeostasis. In this review, we discuss the current evidence and possible pathophysiological mechanisms, and we provide directions for further research. We conclude by suggesting the effect of SGLT2 inhibitors on Mg²⁺ homeostasis is a class effect, with certain patients gaining significant benefits. Further studies are needed to examine whether SGLT2 inhibitors can become a desperately needed novel class of medicines in treating hypomagnesemia.
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In one study, serum magnesium (Mg++) concentration was measured in samples of blood collected from 193 patients admitted to postoperative ICUs wherein 117 patients (61%) had hypomagnesemia (serum Mg less than 1.5 mEq/L or 1.7 mg/dl). The study concluded that hypomagnesemia was common in postoperative ICU patients and patients with severe hypomagnesemia had a higher mortality.13 However, the type of surgeries were not mentioned in this study.
Magnesium (Mg++) deficiency can result in life-threatening complications. The incidence of hypomagnesemia, as well as any coexisting hypokalemia and Electrocardiography (ECG) abnormalities, was studied in patients undergoing major gastrointestinal (GI) surgeries.
This observational study on 51 consecutive adult Intensive Care Unit (ICU) patients recorded serum Mg++ and serum potassium (K+) levels, and 12 lead ECGs, preoperatively and postoperatively, at 48 h and 72 h. Paired “t” test, Pearson Correlation Coefficient and chi-square test were used to statistically assess the difference, correlation, and association between serum Mg++, serum K+, and abnormal ECGs, respectively.
Mean values for serum Mg++ were 1.72 mg/dl and 1.71 mg/dl on day 2 and 3 postops, respectively, while for serum K+ it was 4.14 meq/l and 4.02 meq/l. The incidence of postop hypomagnesemia was 52.9% with a 95% confidence interval (39.2–66.2) on Day 2 and 47.1%, with a 95% confidence interval (33.7–60.7) on Day 3. The incidence of coexisting hypokalemia was 33.3% on Day 2 and 29.2% on Day 3. There was no significant difference between pre and postop serum Mg++ and serum K+ values. The incidence of abnormal ECG was 33.3% on Day 2 postop and 28.6% on Day 3 and had a significant association with incidence of hypomagnesemia on Day 2 (P = 0.02).
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Magnesium (Mg²⁺) is an important intracellular cation and essential to maintain cell function including cell proliferation, immunity, cellular energy metabolism, protein and nucleic acid synthesis, and regulation of ion channels. Consequences of hypomagnesemia affecting multiple organs can be in overt or subtle presentations. Besides detailed history and complete physical examination, the assessment of urinary Mg²⁺ excretion is help to differentiate renal from extra-renal (gastrointestinal, tissue sequestration, and shifting) causes of hypomagnesemia. Renal hypomagnesemia can be caused by an increased glomerular filtration and impaired reabsorption in proximal tubular cells, thick ascending limb of the loop of Henle or distal convoluted tubules. A combination of renal Mg²⁺ wasting, familial history, age of onset, associated features, and exclusion of acquired etiologies point to inherited forms of renal hypomagnesemia. Based on clinical phenotypes, its definite genetic diagnosis can be simply grouped into specific, uncertain, and unknown gene mutations with a priority of genetic approach methods. An unequivocal molecular diagnosis could allow for prediction of clinical outcome, providing genetic counseling, avoiding unnecessary studies or interventions, and possibly uncovering the pathogenic mechanism. Given numerous identified genes responsible for Mg²⁺ transport in renal hypomagnesemia over the past two decades, several potential and specific molecular and cellular therapeutic strategies to correct hypomagnesemia are promising.
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Supported in part by the Henry K. Beecher Memorial Anaesthesia Research Laboratories at Massachusetts General Hospital.

Manuscript received May 16; revision accepted July 18.

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Chest

clinical investigations in critical careHypomagnesemia in Patients in Postoperative Intensive Care

Section snippets

Subjects

Design of Study

RESULTS

Frequency of the Problem

SUMMARY

ACKNOWLEDGMENT

Am J Med

Am Heart J

Lancet

Am J Med

Am J Med

Am J Med

Am Heart J

Am J Med

J Surg Res

Measurement of magnesium in human tissues and fluids: a historical perspective.

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clinical investigations in critical care
Hypomagnesemia in Patients in Postoperative Intensive Care