Toxic methemoglobinemia

Introduction to toxic methemoglobinemia Methemoglobinemia is divided into two types: toxic and hereditary. The toxic methemoglobinemia is caused by drugs and oxidants. The methemoglobin is chocolate-like brown. The toxic methemoglobinemia is sometimes severe and requires urgent injection. Beautiful blue. basic knowledge The proportion of illness: 0.002%-0.003% (mostly caused by nitrite poisoning) Susceptible people: no specific population Mode of infection: non-infectious complication:

The cause of toxic methemoglobinemia

(1) Causes of the disease

1. Drugs and chemicals

(1) Nitric acid and nitrous acid: Nitrite (NO2-) can directly convert Hb in red blood cells into MHb in vivo or in vitro (in vitro), for example, drinking contaminated water or well water, eating rot Deteriorated vegetables (so-called "cabbage poisoning"), vegetable juices, preserved foods, and even toxic MHbemia caused by direct misuse of sodium nitrite, have been reported in many literatures, some drugs such as ethyl nitrite, Asia Both propyl nitrate, isoamyl nitrite and nitroglycerin can cause toxic MHbemia.

(2) Antipyretic and anti-inflammatory drugs: aromatic amines or nitrobenzenes do not oxidize Hb in test tubes, but can induce MHbemia after ingestion into the human body. Common antipyretic and anti-inflammatory drugs such as acetanilide, phenacetin Sulfathiazole belongs to this class.

(3) Local anesthetics: Some local anesthetics can induce MHbemia. It is reported in the literature that intravenous drip of procaine will cause temporary MHbemia of varying degrees in all patients, pharyngeal anesthesia, spray once Procaine is likely to induce severe MHbemia, and benzocaine (ethyl aminobenzoate) also falls into this category.

(4) Other drugs: such as acetophenone, primaquine, resorcinol (Resorcin) can cause MHbemia, an anti-leprosy drug dapsone (dapsone), used in recent years to treat AIDS Complications - Pneumocystis carinii pneumonia, often induced MHb.

(5) Other chemical products: factories that produce aniline, nitrobenzene and their derivatives can invade the human body through the skin or respiratory tract. Aniline dyes such as ink, crayons, shoe polish, etc. should be avoided in contact with infants and children.

2. Environmental pollution

In addition to the aniline and nitrobenzene derivatives contained in wastes and waste gas from chemical plants, insecticides (benzoylphenylurea) and aromatic amine herbicides (propanile) induce MHb blood. It has been reported that residents of industrial polluted towns and waste dumps have increased MHb levels in their blood.

3. Age factor

Due to the immature development of the enzyme system in infancy, especially in premature infants, b5R activity in red blood cells is significantly lower than that in adults. In addition, the intestinal pH of infants is higher. It is beneficial to intestinal bacterial reproduction and converts NO3- into more N02-, therefore, infants are more prone to toxic MHbemia, and the disease is more serious, the mortality rate is higher, the literature reported that infant diarrhea will cause a significant increase in blood MHb in about half of children.

4. Individual differences

For the same incentives, the responses between different people are quite different, especially for drugs that are not directly acting. Because of the absorption, metabolism, and degree of conversion of drugs, and the difference in intracellular reducing ability, the clinical manifestations are inconsistent. The susceptibility of humans to diseases is mainly determined by genetic factors. It has been found that although heterozygotes of congenital MHbemia do not occur, exposure to inducement is more likely to cause toxic MHbemia than normal people.

(two) pathogenesis

Under normal circumstances, hemoglobin (Hb) contains divalent iron, which combines with oxygen in the lungs to release oxygen into the tissue. During the oxygenation process, a small portion of hemoglobin iron is oxidized to trivalent iron, called methemoglobin (MetHb). It is a brown pigment. The methemoglobin contained in normal human blood is equivalent to 0.4% to 1.7% of the total hemoglobin. The methemoglobin cannot carry oxygen, but it can still be reduced to hemoglobin. When the blood methemoglobin increases, it is called high iron. Hemoglobinemia, red blood cell reduction system has three: one is nicotinamide adenine dinucleotide (NADH) MetHb reductase, which is NADH-cytochrome b5 reductase, which can utilize uronic acid pathway and glycolysis process The NADH produced by the flavin adenine dinucleotide (FAD) transmits electrons to the cytochrome b5, the reduced form b5 acts directly on the MetHb, and reduces it to Hb. Amide adenine dinucleotide phosphate (NADPH) reductase, which utilizes NADP produced by the pentose phosphate pathway to reduce MetHb to Hb, but requires some artificial dyeing due to the lack of natural electron transporters. As methylene blue, in order to activate the system, the other three are non-enzymatic reductants, such as vitamin C, glutathione, Hb and oxidation of MetHb MetHb reduction of Hb (FIG. 2).

Toxic methemoglobinemia prevention

Avoid using drugs and harmful substances that can cause poisoning methemoglobinemia.

Symptoms of toxic methemoglobinemia Complication

Generally no complications.

Toxic methemoglobinemia symptoms common symptoms fatigue and cyanosis

The onset can be urgent, the lips, mucous membranes, and nail bed are obviously blue-gray hairpins. There are many medical history of taking certain drugs or exposure to poisons. It can be a common disease. The symptoms of sudden cases are obvious, accompanied by headaches, fatigue, etc. The content of MHb in the medium exceeds 50% to 70%, which may cause disturbance of consciousness and even life-threatening.

Examination of toxic methemoglobinemia

1. Visual observation of heparin anticoagulation in the medium test tube, the blood is brownish brown, the color does not change after shaking for 1 min in the air, or take 1 drop of peripheral blood on the filter paper, the color is still visible after shaking for 30s in the air. Brown, if necessary, with normal blood control, the above test can rule out hypoxic hair loss caused by respiratory or circulatory failure.

2. Absorption spectrum of MHb Blood is diluted 5 to 20 times with distilled water, and directly observed with a spectroscope. There is one dark band in the red zone, and 10 drops of potassium cyanide (sodium) or dithionke is added. The band disappeared, or the wavelength of the recording spectrophotometer was used to scan, and the change of the absorption spectrum around 630 nm before and after the addition of potassium cyanide was observed. The test should have a normal blood control.

3. MHb quantitative determination The MHb content was determined by Evelyn and Malloy spectrophotometry.

4. MHb reduction test A little methylene blue was added to the blood and placed in a 37 ° C water bath for 30 to 60 minutes. The MHb disappeared and the color turned red.

According to the condition, clinical manifestations, symptoms, signs, you can choose to do electrocardiogram, biochemistry, electrolytes and other tests.

Diagnosis and diagnosis of toxic methemoglobinemia

According to the medical history, clinical manifestations and laboratory tests are generally not difficult to make a diagnosis.

Differential diagnosis

1. Hypoxic cyanosis due to respiratory or circulatory system caused by hypoxia in the body, when the deoxygenated Hb in the blood reaches 50g / L, the clinical manifestations of cyanosis, but the oxygen-deficient blood will immediately turn into bright red when exposed to air,

2. Sulfated hemoglobinemia can cause MHbemia in certain drugs, can also induce sulphur hemoglobin (SHb). Currently, the commercially available Hb automatic analyzer is generally based on multi-wavelength correction calculation results, SHb will be wrongly Counting "MHb", blindly relying on laboratory reports, often make a wrong diagnosis, therefore, when the trial of methylene blue treatment is invalid, you should first consider the combined SHbemia,

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