ACUTE POISONING – General Considerations, Clinical Presentation, General Management, Specific Measures, Forced Diuresis and Dialysis and Hemoperfusion
The high incidence of poisoning is attributed to the widespread use and free availability of insecticides, pesticides and other harmful chemicals for use in agriculture and industry. Depending upon the cost and local availability, varied substances are used. In the order of frequency, the toxic agents include organophosphorus compounds, barbiturates, benzodiazepines, vegetable poisons, phenothiazines, corrosive acids, and several others. The precipitating factors, which drive persons to commit suicide, are depressive illness, financial problems, domestic conflicts, and frustration in studies and jobs or incurable illness. Among epileptics and alcoholics the incidence of suicidal poisoning is high. Accidental poisoning is common in children. Persons engaged in the use of toxic chemicals in agriculture and in industry are liable to suffer if proper safety precautions are not adhered to.
Though poisoning by many chemicals lead to characteristic clinical features, in the majority of cases symptoms are non-specific and may be mistaken for other acute illnesses. The common presentations are coma, acute psychosis, convulsions, gastroenteritis, circulatory collapse, or pulmonary edema.
Corrosive poisons produce noticeable lesions at the points of maximum contact such as the mouth, esophagus and stomach. Other poisons affect specific organs maximally, e.g. liver damage in paracetamol poisoning, renal damage in copper sulphate poisoning, and cardiac dysfunction in Cerebera odollam poisoning. Poisons consumed on an empty stomach are absorbed more rapidly than if taken on full stomach. Also, if taken along with alcohol, many poisons are quickly absorbed and their damaging effects are cumulative.
Diagnosis is rendered easy if proper history or evidence of the material is obtained, but in many cases such help is not available. A high index of suspicion on the part of the physician is absolutely necessary for arriving at an early diagnosis in such cases. Abrupt occurrence of acute illness in a person who is in good health should suggest acute poisoning as a possibility. Smell of alcohol or kerosene, severe respiratory depression, circulatory collapse, convulsions, constricted pupils, cardiac arrhythmias, dystonic postures, and muscle fasciculations add support to this diagnosis.
The outcome depends upon factors like:
1. The amount of poison and its mode of administration,
2. Presence of food in the stomach at the time of ingestion,
3. Delay in starting treatment,
5. General health and concurrent illness, and
6. Availability of specific antidotes.
Patients who are comatose due to acute poisoning face the twin dangers of the toxic-effects of the chemical and the grave consequences of an obstructed airway.
Acute poisoning is a medical emergency and is best treated in a well-equipped hospital with teams specially trained to handle such cases. Since in many cases the nature of the poison will not be evident at first, the aim of treatment is to keep the patient alive with support of vital functions, eliminate as much of the poison as possible from the body and prevent further absorption of poison. Specific antidotes are given as soon as the nature of the poison is known. Selective antidotes are available only for 2% of such poisons.
Most important is to clear the airway and ensure adequate ventilation by positioning, suction, or by insertion of nasal or oropharyngeal airway. The respiration should be clinically assessed and if there is ventilatory impairment necessary support with supplemental oxygenation and mechanical ventilation should be instituted. Intermittent positive pressure respiration has to be started with endotracheal intubation, if conservative measures fail. The patient should be turned from side to side at four-hourly intervals to prevent aspiration and hypostatic pneumonia. Frequent bronchial suction helps to prevent atelectasis and aspiration pneumonia.
Shock is managed on the usual lines. Maintenance of fluid and electrolyte balance is of utmost importance in all cases.
Decontamination of skin
Pesticides and other chemicals which are present on the cloths and skin get absorbed through the skin and worsen the condition. Similarly corrosive agents rapidly injure the skin and eyes. In these situations washing the affected area with large quantities of water and soap prevents further systemic absorption of the toxin. Normal saline is preferred for irrigation of the eyes.
An intake output chart should be maintained and a urine output of at least 1500 mL should be ensured. Replacement of electrolytes and correction of acidosis should be done with proper laboratory monitoring. Maintenance of nutrition is equally important. Diet containing 2000 calories should be given orally if the patient is conscious. In unconscious patients food has to be given through a nasogastric tube. Parenteral nutrition has to be started in severely affected patients.
Repeated examination of blood and urine for the level of the toxic agent helps to monitor the progress with treatment.
a. Ingested poisons
In many cases of ingested poisons, considerable amounts remain in the gastrointestinal tract up to four hours; hence it is absolutely necessary to take appropriate measures for their removal. Induction of vomiting is safe in conscious patients. Vomiting is induced by tickling the pharynx or administration of gastric irritants such as concentrated common salt solution 200-400 mL. In the case of corrosive poisons and highly irritant substances like kerosene, emesis and gastric intubation are contraindicated. Gastric lavage by using a stomach tube is an effective method to empty gastric contents rapidly and this can be done even in unwilling patients. This is the method of choice in all conscious patients who have consumed noncorrosive poisons. However, it is risky in comatose patients due to the danger of aspiration into the respiratory tract and in such cases aspiration through Ryle’s tube is preferable. Gastric contents should be preserved in a sealed bottle for chemical examination and further medicolegal procedures. Use of activated charcoal, which adsorbs many toxins reduces gastric and intestinal absorption further. Dose is 50-200 g in 200 mL water initially and 50 g 6 hourly till recovery. The surface area of activated charcoal is increased several folds, compared to the parent substance and this large surface area adsorbs several substances non-specifically.
Purgatives such as magsulph. 15-30 g or sorbitol 1 g/kg bw (maximum of 150 g) orally followed by bowel wash 2 hours later help to eliminate the poison from the intestine.
b. Removal of absorbed poisons
Forced diuresis enhances the renal excretion of many poisons. Hemodialysis helps to eliminate many water soluble substances.
The kidneys can be made to eliminate poisonous drugs at a rate consistent with the urine output. Contraindications include congestive cardiac failure, renal failure, rhabdomyolysis and cerebral edema. In an unconscious patient a Foley’s catheter should be introduced to facilitate uninterrupted flow of urine and for proper monitoring of output.
Dialysis and Hemoperfusion
Since most of the cases recover with forced diuresis, hemodialysis is indicated only in a few. Indications for hemodialysis are: (a) high blood levels of the drug, (b) renal failure, and (c) non-responsiveness to forced diuresis and (d) poisoning associated with deep coma, hypotension and fluid and electrolyte disturbances. In the absence of facilities for hemodialysis, peritoneal dialysis should be undertaken. Hemodialysis is 6-10 times more efficient than peritoneal dialysis.
Hemoperfusion is the process of passing the patient’s blood through cartridges packed with activated charcoal, which adsorbs drugs and toxins such as barbiturates, carbamazepine, glutethimide, meprobamate, methaqualone and several others.
Multiple dose activated charcoal Doses of activated charcoal 1-2g/kg bw repeated every 2-4 hours hasten elimination of drugs by adsorption of drugs excreted into the gut lumen (gut dialysis).
Antidotes are available for 2% of the poisonous substances. These may be chemical antidotes, which neutralize the action of the poison, or biological antidotes, which prevent their pharmacological response. They should be employed only after ascertaining the nature of the poison. In most cases, the antidote is indicated by the manufacturers on the packing of the toxic chemical
Many of the patients with suicidal poisoning attempt to repeat these episodes because of their psychiatric problems. Hence, it is necessary to instruct their relatives and also arrange for proper psychiatric treatment after the initial episode is treated.
This is employed when the toxin is removable by the kidney and the metabolites are toxic to the system. A substantial proportion of the poison is excreted in the urine unchanged. The poison should be distributed mainly in the extracellular fluid and only minimally bound or not bound at all to proteins.
Elimination of the toxic substance is enhanced by manipulation of the urine pH so as to render the toxin in the ionized form. Forced diuresis should be considered, and may be indicated, in poisoning due to the following substances.
1. Fluid overload
2. Pulmonary edema
3. Cerebral edema
4. Electrolyte and acid-base disturbances.
Diuresis is induced by giving 5% glucose continuously IV as drip and frusemide IV in dose of 20 mg 6th hourly depending on the response. Proper estimation of electrolytes and acid-base states should be undertaken during and after the procedure.
Forced acid diuresis
The urine pH is adjusted to 5.5-6.5 by giving: 10 g arginine or lysine hydrochloride intravenously over 30 minutes followed by ammonium chloride 4 g 2 hourly, by mouth.
Forced alkaline diuresis
The urine pH is adjusted to 7.5-8.5 by giving boluses of 50 mmol (approx 50 mL) of 7.5% sodium bicarbonate solution. Often 200-300 mmol is required in the first 1-2 hours. Since a large sodium load is being given with the bicarbonate cardiac failure may be precipitated in susceptible individuals.
DIALYSIS AND HEMOPERFUSION
In hemodialysis, materials, which are dialyzable including toxic materials, are dialyzed across a semipermeable membrane, using appropriate solutions, which will permit the removal of the toxic substance. Dialysis machines are available in several hospitals offering secondary care.
Hemoperfusion is the removal of the toxic material by perfusion of blood through a cartridge containing material, which will absorb the particular substance.
Requisites for Instituting Dialysis Procedures
1. The drug or toxic substance should diffuse easily through the peritoneum or dialysis membrane or be readily adsorbed to activated charcoal or uncharged resin.
2. A significant proportion of the poison should be present in plasma water or be capable of rapid equilibration with it.
3. The pharmacological effect of the substance should be directly related to the blood concentration.
4. Antidote is not easily available.
Depending on the situation any one of the procedures can be adopted. Compared to peritoneal dialysis, the other procedures are thrice more efficient.
Indications for Dialysis and Hemoperfusion
1. Severe clinical intoxication as shown by grade IV coma, hypotension, hypothermia and hypoventilation caused by hypnotic drugs
2. Progressive clinical deterioration, despite adequate supportive management.
3. High plasma concentration of the toxic agents. Drugs that can be effectively dialysed includes barbiturates, phenytoin, primidone, paraldehyde, chloral hydrate, amphetamine, alcohols, methanol, ethylene glycol, salicylates, paracetamol, several antibiotics, isoniazid, quinine, quinidine, metallic salts including lithium, bromide, iodide and potassium, ergotamine, carbon tetrachloride toxic principles of mushrooms and others.
1. The toxic substance is a rapid acting metabolic poison.
2. The effect of the substance is irreversible, e.g. organophosphorus compounds.
3. The drug is relatively non-toxic, e.g. benzodiazepines.
4. The drug has a very large volume of distribution.
5. Cardiogenic shock.
1. Thrombocytopenia (about 30% reduction)
2. Leucopenia (about 10% reduction)
3. Loss of clotting factors.
4. Lowering of calcium, glucose
5. Bleeding tendency due to heparinization
6. Patient may disconnect shunt lines
7. Air embolism
The choice of elimination technique should depend upon the plasma level of the substance.