Hypomagnesemia

Introduction to hypomagnesemia The total amount of magnesium in the body is about 1000mmol (22.66g), which is the most abundant cation in the body except for sodium, potassium and calcium. 50%~60% is present in the bone, and only in the extracellular fluid. 1%, the concentration of magnesium [Mg2] in the serum is 0.75 to 0.95 mmol/L (1.7 to 2.2 mg/dl, or 1.5 to 1.9 mEq/L). Except for bones, muscle contains more magnesium, and blood magnesium concentration does not represent changes in total magnesium in the body. Magnesium is widely distributed in moving, plant cells. Magnesium ion is one of the most important ions in the human body. It ranks second only to potassium in the content of liquid cations in cells, but the concentration in extracellular fluid is very low. The physiological function of magnesium is quite complicated. Magnesium ion disorder is a relatively common electrolyte disorder, but its clinical manifestations lack specificity and are easily overlooked. basic knowledge Probability ratio: 0.5% ratio Susceptible people: no special people Mode of infection: non-infectious Complications: hypokalemia

Cause of hypomagnesemia

(1) Causes of the disease

Insufficient magnesium intake (30%):

If the magnesium intake is strictly limited, the serum magnesium concentration may decrease within 1 week, the urinary magnesium excretion may also be significantly reduced, and the magnesium concentration in the red blood cells may also decrease. If the magnesium intake is strictly limited for 5 to 6 weeks, clinically The symptoms of hypomagnesemia may occur. Patients after gastrointestinal surgery are fasted, only general intravenous nutrition is given, magnesium is not paid attention to, and transient mild hypomagnesemia may occur; in critically ill patients, it is prone to occur. In the case of chronic low intake, patients with obvious hypomagnesemia, severe malnutrition or excessive consumption, during the recovery period, due to strong anabolism, the utilization of magnesium in the body increases, and the intake is relatively insufficient. In women with mild to moderate hypomagnesemia, lactation or pregnancy, infants and young children may have mild hypomagnesemia if they do not pay attention to increasing magnesium intake.

Gastrointestinal disease (15%):

Hypomagnesemia due to gastrointestinal diseases is not uncommon in clinical practice, but it is easily overlooked. Such as most of the small intestine resection; malabsorption syndrome; pancreatitis; various intestinal inflammation; long-term vomiting caused by a variety of reasons, diarrhea, gastrointestinal decompression drainage can cause increased intestinal magnesium excretion, while also having magnesium Insufficient intake can cause hypomagnesemia.

Excessive urinary magnesium excretion (40%):

The kidney is the main factor regulating magnesium metabolism. The increase of magnesium excretion in the kidney is a common cause of hypomagnesemia, which is mainly found in the following aspects.

(1) Diuretics: Most diuretics have magnesium-discharging effect. If used excessively, it can increase urinary magnesium excretion, but usually the symptoms are mild, which is often overlooked in clinical practice, but only pay attention to the problem of potassium ions.

(2) Digitalis drugs: These drugs can inhibit the reabsorption of magnesium by renal tubules. In hypomagnesemia, digitalis poisoning is prone to occur with or without hypokalemia, so digitalis drugs are used. Patients should not only pay attention to the supplement of potassium ions, but also pay attention to the supplement of magnesium ions.

(3) renal tubular dysfunction: renal lesions including renal tubular damage and renal interstitial damage can cause the absorption of magnesium ions to decline, causing hypomagnesemia.

(4) Alcoholism: A large amount of ethanol can inhibit the reabsorption of magnesium by the renal tubules, and hypomagnesemia is prone to occur when drinking alcohol for a long time.

(5) Hypercalcemia: Due to the competitive relationship between calcium and magnesium reabsorption, magnesium reabsorption will decrease when calcium reabsorption increases.

(6) Endocrine diseases: Hyperaldosteronism, hyperparathyroidism can reduce the reabsorption of magnesium in the kidneys.

(7) Other drugs: such as anti-tumor drugs cisplatin, aminoglycoside antibiotics, cyclosporine can cause renal tubular reabsorption of magnesium.

Magnesium distribution (10%)

The extracellular fluid of magnesium enters the intracellular fluid, which can cause metastatic hypomagnesemia, which is commonly found in the following aspects:

(1) Hungry bone syndrome: After removal of parathyroid adenoma, serum magnesium, calcium and phosphorus are significantly reduced, especially in patients with bone lesions before surgery. The reason for the decrease of serum magnesium, calcium and phosphorus is During the bone repair process, a large amount of the above substances are deposited in the bone, and the amount of urine discharged is also reduced.

(2) Recovery period of malnutrition: anabolic metabolism is enhanced, and a large amount of magnesium enters the cell.

(3) Acid-base balance disorder: When alkali poisoning, magnesium ions enter the cell.

(two) pathogenesis

Patients with hypomagnesemia are often accompanied by hypokalemia, although low potassium, low magnesium can be caused by the same cause, such as diarrhea, burns, polyuria, primary aldosteronism, Bartter syndrome and Gitelman syndrome, and diuretics Application, etc., but hypomagnesemia itself may also lead to hypokalemia. In some patients, if magnesium deficiency is not corrected, hypokalemia is difficult to correct. Hypokalemia may be due to abnormal Na+-K+-ATPase. Intracellular K+ deficiency combined with renal potassium loss, the mechanism of renal potassium loss during hypomagnesemia is not fully understood, and many evidences suggest that low magnesium can cause excessive secretion of potassium from the medullary and cortical collecting ducts. Because the medullary sputum has a potassium secretion channel, the channel is normally inhibited by ATP, and the channel inhibition is relieved at low magnesium, resulting in a large secretion of potassium.

About half of patients with hypomagnesemia are associated with hypocalcemia, mainly due to a decrease in PTH secretion due to Mg2+ deficiency. In addition, patients with hypomagnesemia have low levels of 1,25-(OH)2D3 in circulation, and effector tissue exists in PTH. Resistance to vitamin D can also lead to hypocalcemia.

The main pathophysiological changes of hypomagnesemia are neuromuscular excitability, metabolic disorders and tissue and organ damage.

The mechanism of neuromuscular abnormalities has the following two aspects: First, magnesium has the function of stabilizing axons, and the decrease of serum magnesium concentration lowers the threshold of axon excitation and increases the nerve conduction velocity. Magnesium can also inhibit calcium entry into synapses through competition. The anterior nerve endings cause a large number of neurotransmitters to release, causing high reactivity of the neuromuscular. Second, magnesium can also act by affecting calcium transport of muscle cells.

The main reasons for the loss of magnesium in the gastrointestinal tract are as follows.

(1) After the majority of small intestine resection: the time of food passing through the intestine is significantly shortened, and magnesium is absorbed slowly in the intestine. At this time, the absorption will be more reduced, and even the amount of absorption and absorption will be almost equal, resulting in low magnesium. Blood, urinary magnesium excretion is significantly reduced, less than 10mg per day.

(2) malabsorption syndrome: those with fatty diarrhea are prone to hypomagnesemia, because magnesium can form magnesium soap which is not easily absorbed in the intestines and fats. At this time, if fat intake is restricted, magnesium absorption increase.

(3) Pancreatitis: In acute necrotizing pancreatitis, fat necrosis around the pancreas forms fatty acids, fatty acids and magnesium ions, calcium ions form magnesium soap, calcium soap, which leads to reduced absorption of magnesium ions and calcium ions, thus appearing in patients with pancreatitis Stage serum magnesium ion, calcium ion concentration decline is a sign of necrotizing pancreatitis, chronic pancreatitis, can lead to insufficient secretion of digestive enzymes, fat digestive disorders, so that magnesium absorption is insufficient.

(4) various intestinal inflammation: such as non-specific enteritis, chronic ulcerative colitis, Crohn's disease, bacterial dysentery, intestinal fistula, biliary fistula, etc. can cause magnesium absorption disorders.

(5) Long-term vomiting caused by various reasons, diarrhea, gastrointestinal decompression drainage can cause increased intestinal magnesium excretion, and at the same time there is insufficient magnesium intake, which can cause hypomagnesemia.

Hypomagnesemia prevention

Patients with hypomagnesemia may be given prophylactic doses of magnesium as early as possible. For example, patients who are treated with parenteral nutrition should be supplemented with magnesium. Patients who have long-term use of diuretics and have a poor diet should also be supplemented with magnesium. Regularly monitor the level of magnesium ions.

Hypomagnesemia complications Complications hypokalemia

Hypomagnesemia is easy to be associated with hypokalemia and hypocalcemia. When low magnesium causes hand and foot convulsions, low calcium and low potassium are often concerned, so unexplained hypokalemia and hypocalcemia are found. No presence of hypomagnesemia.

Symptoms of hypomagnesemia Common symptoms, convulsions, weakness, facial sniper, terrasse, positive stagnation, coma, dizziness

Because mild magnesium deficiency can be asymptomatic, symptomatic, symptoms are not specific, and often accompanied by other electrolyte disorders, it is difficult to identify clinically, the main clinical manifestations are as follows.

Neuromuscular

Muscle weakness, paralysis, convulsions, muscle fiber tremors, dizziness, ataxia and apathy, these symptoms are similar to calcium deficiency, but also may have facial signs and beam arm signs positive, in addition to nystagmus, swallowing disorders, shallow Reflexes are weakened or weakened, convulsions and coma, and mental manifestations can be manifested as depression, delusion, restlessness, anxiety, irritability, hallucinations, confusion, and loss of orientation.

2. Heart

There may be arrhythmia, such as frequent atrial or ventricular premature contraction, multi-source atrial tachycardia, ventricular tachycardia and ventricular fibrillation, the latter can lead to sudden death, magnesium deficiency can also induce heart failure It is easy to cause digitalis poisoning when treating patients with heart failure with digitalis. The PR interval is prolonged on the electrocardiogram, the QRS wave is broadened, the QT interval is prolonged, the ST segment is moved down and the T wave is widened, low or inverted and u wave.

3. Metabolic performance

Magnesium is important for the energy production of anaerobic and aerobic metabolism in carbohydrate metabolism. Magnesium deficiency can cause abnormal glucose tolerance, and atherosclerosis can be caused by metabolic changes. In the experiment, magnesium deficiency has been shown to cause High triglyceride and hypercholesterolemia.

4. Skeleton

Osteoporosis and osteomalacia can occur in persistent magnesium deficiency.

Examination of hypomagnesemia

1. Determination of serum magnesium concentration: serum magnesium concentration decreased, less than 0.5mmol / L is the main indicator for the diagnosis of hypomagnesemia.

2. Determination of 24h urinary magnesium excretion: If the amount of loss increases, it is caused by renal factors, endocrine factors, metabolic factors and drug factors (see the cause of the disease), otherwise it is caused by intestinal dysfunction or abnormal distribution.

3. Magnesium load test: 16h urine was taken, and the urine magnesium output was measured. If it is greater than 70% of the input, it means that there is no magnesium deficiency in the body; if it is less than 20%, it means magnesium deficiency in the body.

4. Magnesium sulfate treatment test: 25% of magnesium sulfate 8 ml (2 g of magnesium sulfate) was added intravenously to a 5% dextrose solution, and if the symptoms improved, it indicated magnesium deficiency in the body.

5. Electrocardiogram examination: arrhythmia may occur, such as frequent premature contraction, or premature ventricular contraction, multi-source atrial tachycardia, etc., prolongation of PR interval, prolongation of QT interval, ST segment Downshift and T wave widening, low level or inversion and u wave.

Diagnosis and diagnosis of hypomagnesemia

Magnesium ions affect the energy metabolism of central nervous cells. If patients have underlying diseases or incentives that cause magnesium loss, they should be alert to the possibility of hypomagnesemia when neuropsychiatric symptoms occur. You can quickly check serum magnesium <0.75mmol/L. Diagnosis, magnesium tolerance test for magnesium deficiency in the body.

1. The sensitivity of the body to digitalis in the low magnesium state is increased, and it is easy to induce digitalis poisoning.

2. Low magnesium can cause a variety of arrhythmia, but lack specificity, similar to arrhythmia caused by low potassium and low calcium. Note that in the treatment of acute or severe arrhythmia, serum magnesium should be checked, and the existence of low magnesium factor should not be ignored. .

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