ORGANOPOSPHATE POISONING

ORGANOPHOSPHATE AND CARBAMATE INSECTICIDE SPOSONING

Organophosphate and carbamate insecticides are widely used in agriculture (For crop spray) and at home as insecticides for rodents, cockroach etc. Parathion, DDT, Finis, Baygon, Coopex are commonly used products. Most of the war gases are also organophosphates.

Mode of Action

 Organophosphates and carbamates are also called anticholinestrases because they inhibit the enzyme anticholinestrase resulting in an increased acetylcholine activity at nicotinic and muscarinic receptors and in the central nervous system.

Intoxication may follow:

·         Ingestion (for suicide or accidentally).

·         Inhalation (usually when spraying crops or even at home using insecticide spray for cockroaches and other insects)

·         Dermal absorption

CLINICAL FEATURES

Time from exposure to the onset of toxicity varies from minutes to hours but usually is between 30 min to 2 hours. Most patients recover within 24-48 hours but some insecticides may affect for weeks to months.

Muscarinic effects:

·         GIT:    nausea, vomiting, abdominal  colic, diarrhea, tenesmus (due to increased gut motility) sweating, hypersalivation and fecal incontinence.

·          

RESP: dyspnea, cough, wheezing, increased bronchial secretions, pulmonary edema. Death is usually due to respiratory arrest.

·         Urinary: increased urinary frequency and incontinence.

·         EYE:    Miosis, blurred vision.

·         Heart:   bradycardia, hypotension, heart block in severe cases.

Nicotinic effects:

·         Muscle twitching, fasciculations and muscle weakness. In severe cases paralysis of limb, respiratory and extraocular muscles.

·         Hypertension and tachycardia.

CNS effects:

Anxiety, restlessness, tremor, convulsions, confusion and coma.

COMPLICATIONS:

1.       Loss of consciousness

2.       Respiratory failure (due to aspiration, excessive secretions, pneumonia, septicemia or ARDS). Cause of death is usually respiratory failure.

3.       Aspiration pneumonia: due to vomiting in altered consciousness may be aspirated.

4.       Urinary tract infection.

5.       Septicemia.

DIAGNOSIS

Usually the diagnosis is clinical. History is available from the patient or relatives. It may be confirmed by measuring RBC and plasma cholinesterase activity: a reduction of cholinesterase activity in red blood cells and plasma to less than 50% of normal confirms the diagnosis of organophosphate poisoning.

MANAGEMENT

Oxygen: Admit the patient in ICU and give supplementary oxygen.

Gastric lavage: If the agent was recently ingested, empty the stomach by gastric lavage and administer activated charcoal.

·         Do not induce vomiting because of risk abrupt onset of seizures and aspiration.

·         If the insecticide is one the victim’s skin or hair, wash with soap and water.

Atropine:  Atropine reverses excessive muscarinic stimulation and is effective treatment of salivation wheezing, abdominal cramp and sweating.

Administer atropine 2 mg IV every 15 min until bronchial and other secretions are controlled. Repeated doses or constant atropine infusion (0.02-0.08 mg/kg/hour) may be necessary for several days. Atropine causes tachycardia, if heart rate is more than 130/min then for protection of heart reduce the heart rate with IV diltiazem or propranolol (we have IV verapamil instead of diltiazem and metroprolol instead of propranolol in Pakistan).

Pralidoxime (Contrathion):  It is a specific antidote that reactivates cholinestrases and is indicated for nicotinic symptoms due to organophosphate poisoning.

Dose is 1-2 g IV over 5-20 min (one vial of Contrathion contains 200 mg Pralidoxime and costs Rs. 500)   i-e. 5-10 vials of Contrathion are diluted in 100 ml of water for injection. The dose may be repeated every 4-6 hours or start continuous infusion at the rate of 10 mg/kg/hr. Continue Pralidoxime as long as there is any evidence of acetylcholine excess.

(Signs of full atropinization: dry hot skin, dry secretions, pulse more then 70/min and dilated pupils).

Mechanical ventilation:

Indication

·         Excessive secretions

·         Depressed level of consciousness: to protect the airway.

·         Poor gas exchange unresponsive to supplementary oxygen.

·         Severe metabolic acidosis with hemodynamic instability (systolic BP<90 mmHg).

Mode of ventilator

SIMV + pressure support mode in either pressure controlled or volume controlled form. Positive end expiratory pressure is applied to keep oxygen saturation >94% at FIO2 40%.

Weaning from ventilator is usually carried out with pressure support weaning and T-tube trial.