What Is Paraquat Poisoning?

Paraquat (PQ) has a brand name such as Sweep Light, Ku Wu Zun, etc. It is a highly effective non-selective contact herbicide with strong toxicity to humans and animals. It can cause acute poisoning by mistake or self-administration. It has become a pesticide. Common causes of deaths from poisoning. The lethal dose for adults is 5 to 15 ml (20 to 40 mg / kg) of a 20% aqueous solution. Paraquat is absorbed through the digestive tract, skin, and respiratory tract, and its toxicity affects multiple organs throughout the body. In severe cases, it can cause multiple organ dysfunction syndrome (MODS). The lung is the main target organ and can cause "paraquat lungs." Early manifestations are Acute lung injury (ALI) or acute respiratory distress syndrome (ARDS), with alveolar and interstitial fibrosis in the later stages, are the main causes of death from paraquat poisoning, with a mortality rate of 50% to 70%.

Basic Information

English name

paraquatpoisoning

Visiting department

Emergency Department

Common locations

Respiratory tract

Common causes

Take paraquat by mistake

Causes of paraquat poisoning

Acute poisoning caused by accidental or paraquat paralysis has become a common cause of death caused by pesticide poisoning.

Clinical manifestations of paraquat poisoning

Common clinical paraquat poisoning is mostly self-administered or by mistake, absorbed through the digestive tract, and injection routes are extremely rare. Intact skin can effectively prevent the absorption of paraquat. Long-term contact, large amounts of contact with contaminated and damaged skin of the scrotum or perineum may still cause systemic toxicity.

Oral poisoning

Have oral burning sensation, oral and esophageal mucosal erosion and ulcers, nausea, vomiting, abdominal pain, diarrhea, and even vomiting, blood in the stool, severe cases with gastric perforation, pancreatitis, etc .; some patients have hepatomegaly, jaundice and abnormal liver function, and even liver Functional failure. There may be dizziness, headache, and a few patients have central nervous system symptoms such as hallucinations, fear, convulsions, and coma. Renal injury is the most common and manifests as hematuria, proteinuria, oliguria, increased blood BUN, Cr, and acute renal failure in severe cases. Lung injury is the most prominent and the most serious, manifested by cough, chest tightness, shortness of breath, cyanosis, dyspnea, physical examination can be found to reduce breathing sounds, lungs can be heard and wet and dry rales. Pulmonary edema and pulmonary hemorrhage occur within 24 hours of large oral intake, and they often die from ARDS within a few days. Those who are not ingested subacutely, with chest tightness and belching in more than 1 week, and dyspnea peaked in 2 to 3 weeks. Patients often die from respiratory failure. A few patients have complications such as pneumothorax, mediastinal emphysema, toxic myocarditis, and pericardial bleeding.

2. Partial exposure to paraquat poisoning

The clinical manifestations are contact dermatitis and chemical burns of the mucosa, such as skin erythema, blisters, ulcers, etc. Burns in the conjunctiva and cornea form ulcers and even perforations. Prolonged and extensive exposure can cause systemic damage and even life-threatening.

3. Injection route (blood vessels, muscles, skin, etc.) in contact with paraquat

Exposure to paraquat by injection (vascular, muscle, skin, etc.) is rare, but the clinical manifestations are dangerous and the prognosis is poor.

Paraquat poisoning check

Chest CT

The performance varies depending on the degree of poisoning. Extremity severe poisoning is mainly exudative, which can invade the whole lung field within a few days. Mild poisoning only shows increased lung texture, scattered focal pulmonary fibrosis, and a small amount of pleural effusion. With time migration, the lesions can be completely absorbed; moderate to severe poisoning shows a gradual change. In the early stage of poisoning (within 1 week), the lung texture is thickened and the interlobular fissures are widened. Mainly take-out, may have pleural effusion. The rapid progress period is 1 to 2 weeks after poisoning, which shows a centripetal progression. The scope of pulmonary exudate-like changes or ground-glass-like changes rapidly expands. If it cannot be terminated, it may invade the entire lung and eventually Died from severe hypoxia. Survivors often automatically stop the progression of lung lesions about 10 days after poisoning, and lung lesions are gradually absorbed in the future, and can be completely absorbed after a few months without leaving any sequelae.

2. Arterial blood gas analysis

Can manifest as hypoxemia, metabolic acidosis, respiratory alkalosis and so on.

3. ECG

He showed tachycardia or bradycardia, arrhythmia, prolonged QT interval, and ST-segment shift.

4. Other

Elevated white blood cell count, fever, anemia, thrombocytopenia, etc. may also occur.

5. Determination of blood and urine paraquat

The severity and prognosis of the disease can be assessed, but at present there is no uniform testing standard in China.

Diagnosis of paraquat poisoning

A clinical diagnosis of acute paraquat poisoning can be made based on a history of paraquat administration or exposure, clinical manifestations, and laboratory tests. Also note the following:

1. Determination of blood and urine paraquat concentration can clearly diagnose and help determine the prognosis, but over time, blood and urine paraquat concentrations gradually decrease or even difficult to measure.

2. The history of paraquat exposure is clear, especially the oral route. Even if the clinical symptoms are mild and there is no evidence of toxicological examination, the diagnosis can still be established. The history of toxicant exposure is unknown, and paraquat is detected in blood and urine. Still established.

3. Patients have typical clinical manifestations, that is, early chemical stomatitis, upper gastrointestinal irritation and corrosion, liver and / or kidney damage, and subsequent lung damage, and the history of toxic exposure is unknown and there is no evidence of blood and urine tests, which can be diagnosed. For suspected paraquat poisoning.

According to the amount of drug taken early, the following types can be made:

(1) The intake of light paraquat is <20mg / kg. Except for gastrointestinal symptoms, other symptoms are not obvious, and most patients can completely recover.

(2) Medium-heavy paraquat intake of 20 to 40 mg / kg, patients may have multi-system involvement in addition to gastrointestinal symptoms, renal and liver damage may occur within 1 to 4 days, and within a few days to 2 weeks Lung injury occurred, and most died of respiratory failure within 2 to 3 weeks.

(3) Fulminant paraquat intake> 40mg / kg, severe gastrointestinal symptoms, died of multiple organ failure within 1 to 4 days.

Paraquat poisoning treatment

There is no clinically effective antidote for acute paraquat poisoning, and its treatment is still being explored. Taking early steps to eliminate poisons entering the body is the basis for successful treatment of acute paraquat poisoning.

1. Block poison absorption

The main measures include vomiting, gastric lavage and adsorption, catharsis, and washing.

(1) Emetic, gastric lavage and adsorption can stimulate the throat to induce vomiting, and race against time. Water for gastric lavage is preferred, and soapy water or a 1% to 2% sodium bicarbonate solution can also be used. The gastric lavage liquid is not less than 5 liters until it is colorless and tasteless. Upper gastrointestinal bleeding can be gastric lavage with norepinephrine ice saline. After the gastric lavage, the 15% bleaching earth solution of the adsorbent was injected.

(2) Catharsis Use 20% mannitol, sodium sulfate or magnesium sulfate to promote catharsis and reduce absorption. Patients can take oral bleaching earth or activated carbon continuously for 2 to 3 days, and can also try Chinese medicine (rhubarb, mirabilite, licorice) for catharsis.

(3) Washing Skin contact persons should immediately take off the clothes contaminated by paraquat or vomit, and thoroughly wash the skin and hair with water and soapy water, so as not to cause skin damage and prevent the absorption of poisons. Paraquat eye contact needs to be rinsed with running water for 15-20 minutes, and then treated by a specialist.

2. Promote the discharge of poison

(1) Rehydration and diuresis All patients with acute paraquat poisoning are dehydrated. Proper fluid rehydration combined with intravenous injection of diuretics is beneficial to maintain circulating blood volume and urine volume (1 to 2 ml / kg / h), to maintain renal function and excretion of paraquat Both are beneficial. Need to pay attention to patients' cardiopulmonary function and urine output.

(2) Blood purification Hemoperfusion (HP) and hemodialysis (HD) are common methods for removing blood circulation poisons and are used for paraquat poisoning, which is still controversial. HD is recommended only for patients with paraquat poisoning with renal impairment. As for HP, it is recommended to take HP as soon as possible after oral paraquat poisoning. The effect is good within 2 to 4 hours. Use one or more perfusion devices at a time according to the concentration of blood poison or oral dose, and then decide whether to do it again based on the concentration of blood paraquat. HP or HD.

3. Drug treatment

Clinically applied drugs are mainly used to prevent and treat target organ lung damage. Commonly used drugs include glucocorticoids, immunosuppressants, and antioxidants.

(1) Glucocorticoids and immunosuppressants Early combined application of glucocorticoids and cyclophosphamide shock therapy may be beneficial to patients with moderate to severe acute paraquat poisoning. Early treatment of patients with non-fulminant moderate to severe paraquat poisoning is recommended. Use methylprednisolone, hydrocortisone, and cyclophosphamide.

Others such as cyclosporine A, recombinant human type II tumor necrosis factor receptor-antibody fusion protein, colchicine, vincristine, etc. are also effective, and evidence-based medical evidence is needed.

(2) Antioxidants Antioxidants can remove oxygen free radicals and reduce lung damage. Superoxide dismutase (SOD), glutathione, N-acetylcysteine (NAC), metallothionein (MT), vitamin C, vitamin E, melatonin, etc. for the treatment of acute paraquat poisoning in animals The experiment has a certain effect, and the clinical research has not obtained the expected results.

(3) Other pharmaceutical protease inhibitors ulinastatin, non-steroidal anti-inflammatory drug sodium salicylate and traditional Chinese medicine preparations such as Xuebijing, Danshen, Ginkgo biloba extract injection, are still in the exploration stage for the treatment of acute paraquat poisoning .

4. Support symptomatic treatment

(1) Oxygen therapy and mechanical ventilation Conventional oxygen should be avoided for acute paraquat poisoning. Based on the understanding of the toxicological mechanism of paraquat poisoning, it is suggested to use PaO ₂ <40mmHg (5.3kPa) or ARDS as an indication of oxygen therapy. There is no evidence that mechanical ventilation increases survival rates, and mechanical ventilation can prolong survival in patients with conditional lung transplantation.

(2) Application of antibiotics Acute paraquat poisoning can cause multiple organ damage. The use of glucocorticoids and immunosuppressants can prevent the use of antibiotics. Macrolides are recommended. These drugs have a certain effect on the prevention and treatment of pulmonary fibrosis. . If there is evidence of infection, a strong antibiotic should be applied immediately.

(3) Nutritional support Those with acute paraquat poisoning who are fasting due to severe digestive tract damage, pay attention to parenteral nutrition support, and give deep vein high nutrition if necessary. The effect of enteral and parenteral nutrition support on the prognosis of acute paraquat poisoning remains to be explored.

(4) Symptomatic treatment For those with frequent vomiting, serotonin receptor antagonists or phenothiazine antiemetics can be used to control symptoms, and dopamine antagonists such as metoclopramide can be avoided, because the drug may reduce the recovery of renal function by dopamine effect. For those with obvious symptoms of corrosion and pain, use analgesics such as morphine, as well as gastric mucosal protective agents and acid inhibitors. Corresponding protective agents are given for organ damage, and physiological functions are maintained.

5. Other treatments

Radiotherapy can control the number of pulmonary fibroblasts and reduce fibrin production. There is no evidence that this method can reduce mortality. Lung transplantation is used in patients with severe irreversible respiratory failure, which has been successfully reported abroad.

6. Monitoring and follow-up

In order to assess the condition and judge the prognosis and guide the treatment, the following monitoring should be performed when conditions are available.

The patient was immediately drawn blood for paraquat concentration at the time of consultation, and monitored every 3 days thereafter. If paraquat was no longer present, the test could be stopped. A semi-quantitative measurement of urinary paraquat is performed daily, and a urine test is started in the morning, once a day until negative. At the same time, check hematuria routine, liver and kidney function, myocardial markers, arterial blood gas analysis, chest radiograph (or lung CT), etc., should be completed within 12 hours after consultation, and monitored at any time if necessary until the condition improves.

Prognosis of paraquat poisoning

Due to the characteristics of paraquat's lung injury, survivors should be followed up for at least half a year and pay attention to reviewing lung, liver, and kidney functions. In view of glucocorticoids and immunosuppressive agents that may cause side effects such as infection and osteonecrosis, family members should be informed before use.

1. The dose is the most important influencing factor for the prognosis of acute paraquat poisoning. First aid measures such as vomiting and gastric lavage can also affect its prognosis. Patients took the drug on an empty stomach, the blood white blood cell count increased significantly, liver and kidney dysfunction, metabolic acidosis, and lung injury appeared earlier, especially those who appeared within 24 hours of poisoning had a poor prognosis.

2. The following conditions do not necessarily cause serious harm: plants that have been sprayed with paraquat diluent; soils that have been sprayed with paraquat; or paraquat diluted by sprayers.

Paraquat poisoning prevention

Strengthen the monitoring of paraquat products to reduce the concentration; ensure the addition of malodorous agents and emetics are qualified to reduce the absorption after accidental ingestion and reduce the harm. Unused paraquat solution should be recycled in time; household paraquat solution should be stored in a safe way to avoid accidental use by children and young children and contact with high-risk groups. Strengthen training to familiarize primary medical staff with the early diagnosis and treatment of acute paraquat poisoning.