Taking methanol by mistake or inhaling methanol vapor is the main cause and way of methanol poisoning. Fake wine and inferior wine contain high concentration of methanol, and drinking this kind of sprinkling will also be poisoned.
Introduction to toxicology
After being absorbed by human body, methanol can be quickly distributed in various tissues of the body, with the highest content in cerebrospinal fluid, blood, bile and urine, higher content in aqueous humor and vitreous humor, and the lowest content in bone marrow and adipose tissue. Methanol is oxidized to formaldehyde by alcohol dehydrogenase after liver metabolism, and then oxidized to formic acid. The oxidation of this product in the body is slow, which is only 1/7 of that of ethanol, and its excretion is also slow, which has obvious accumulation effect. Unoxidized methanol is excreted through respiratory tract and kidney, and part of it is slowly excreted through gastrointestinal tract. It is speculated that the concentration of methanol inhaled by people in the air is 39.3 ~ 65.5 g/m 3 for 30 ~ 60 minutes, which can cause poisoning. Oral administration of 5 ~ 10 ml can cause serious poisoning; Oral administration of 15ml once or 124 ~ 164ml within two days can cause blindness. It is reported that oral administration of 30 ml can cause death. Methanol mainly acts on the nervous system, which has obvious anesthetic effect and can cause brain edema. The anesthetic concentration of methanol is close to LC, so it is more dangerous. It has a special selective effect on optic nerve and retina, which is easy to cause optic nerve atrophy and blindness. Methanol vapor has a strong stimulating effect on respiratory mucosa. The toxicity of methanol is related to the accumulation of its metabolites formaldehyde and formic acid. Previously, it was thought that the toxic effect was mainly caused by formaldehyde, which could inhibit the oxidative phosphorylation of retina, make ATP in membrane unable to be synthesized, denature cells and eventually lead to optic nerve atrophy. Recent studies show that formaldehyde is rapidly metabolized into formic acid, and the metabolic acidosis and eye injury caused by acute poisoning are mainly related to formic acid content. Methanol inhibits some oxidase systems in the body, inhibits the aerobic decomposition of sugar, causes the accumulation of organic acids such as lactic acid and formic acid, and causes acidosis. It is generally believed that the toxicity of methanol is caused by itself and its metabolites.
clinical picture
The main target organs damaged after acute methanol poisoning are central nervous system, optic nerve and retina. The incubation period of inhalation poisoning is generally 1 ~ 72 hours, but also 96 hours; Oral poisoning usually lasts for 8 ~ 36 hours; If ethanol is ingested at the same time, the incubation period is longer.
clinical features
Irritation symptoms: Inhalation of methanol vapor can cause irritation symptoms of eyes and respiratory mucosa. Central nervous system symptoms: patients often have dizziness, headache, dizziness, fatigue, gait faltering, insomnia, apathy, confusion and so on. In severe cases, there are confusion, coma and epileptic convulsions. Severe oral poisoning may cause extrapyramidal damage or symptoms of Parkinson's syndrome. Cranial CT examination revealed symmetrical infarction and necrosis of lenticular nucleus and subcortical central white matter. Symptoms such as hallucinations and depression. Eye symptoms: at first, there are shadows in front of eyes, flashes, blurred vision, eye pain, photophobia, diplopia and so on. In severe cases, the eyesight drops sharply, which can lead to persistent blindness. Examination shows that the pupil is dilated or narrowed, the response to light is slow or disappears, the optic papilla is edematous, the peripheral retina is congested, bleeding and edematous, and there is optic atrophy in the late stage. Acidosis: the binding force of carbon dioxide is reduced, and cyanosis occurs in severe cases, and the breathing is deep and fast, showing Kussmaul breathing.
Symptoms such as digestive system: the patient has nausea, vomiting and epigastric pain. , may be complicated with liver damage. Acute pancreatitis may be complicated by oral poisoning. A few cases were accompanied by tachycardia, myocarditis, S-T segment and T wave changes, acute renal failure and so on. Severe acute methanol poisoning includes severe headache, nausea, vomiting, sharp decline in vision, and even blindness, confusion, delirium, convulsions and coma. Finally, he may die of respiratory failure. According to the history of methanol exposure, the main clinical manifestations in the short term are central nervous system damage, eye damage and metabolic acidosis. According to the field hygienic investigation, it is not difficult to diagnose after comprehensive analysis except other diseases with similar manifestations. When necessary, methanol in blood and urine can be determined. Early poisoning should be differentiated from cold, neurasthenia and acute gastroenteritis. In addition, it should be differentiated from encephalopathy and optic nerve damage caused by acute poisoning of methyl chloride and ethylene glycol and other reasons. It is necessary to inquire about occupational history in detail, conduct on-site hygiene investigation, closely observe the progress of the disease and combine with laboratory examination to get a correct diagnosis.
deal with
The patient should leave the scene immediately and take off the contaminated clothes. Oral patients were given 1% sodium bicarbonate for gastric lavage and magnesium sulfate for catharsis. Remove methanol absorbed in the body. Dialysis treatment: Patients with severe poisoning should be treated with hemodialysis or peritoneal dialysis as soon as possible to alleviate poisoning symptoms, save patients' lives and reduce sequelae. The indications of hemodialysis treatment are: ① blood methanol >; 15.6 mmol/L； Or formic acid >; 4.34 mmol/L； ② Severe metabolic acidosis; ③ Severe visual impairment or papilla retinal edema. Antidote: Ethanol is the antidote to methanol poisoning. The application of ethanol can prevent methanol oxidation and promote methanol discharge. Use 10% glucose solution to prepare 5% ethanol solution, and slowly drip it intravenously. There is not much clinical experience in China. Correction of acidosis: According to blood gas analysis or carbon dioxide binding capacity determination and clinical manifestations, sodium bicarbonate solution or sodium lactate solution should be given as soon as possible. Support and symptomatic treatment: actively prevent and treat brain edema according to the condition, reduce intracranial pressure, improve fundus blood circulation and prevent optic neuropathy. Maintain respiratory and circulatory functions and maintain electrolyte balance. Give a lot of B vitamins. It was suggested that formate and 4- methylpyrazole (4MP) were used to treat methanol poisoning, which was confirmed in the experimental study of monkeys and has not been used in clinic so far.