REVIEW ARTICLE

Year : 2020  |  Volume : 16  |  Issue : 3  |  Page : 101-104

Killer secretions: Organophosphorus poisoning: Practice eessentials and protocols

KP Amrithachandra¹, TP Sreekrishnan², KP Gireesh Kumar^2
1 Amrita School of Medicine, AIMS, Kochi Kerala, India
² Department of Emergency Medicine, AIMS, Kochi Kerala, India

Correspondence Address:
Dr. T P Sreekrishnan
Department of Emergency Medicine, AIMS, Kochi, Kerala
India

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/AMJM.AMJM_19_20

Organophosphorus pesticide self-poisoning is an important clinical problem in rural regions of the developing world and kills an estimated 200,000 people every year. Unintentional poisoning kills far fewer people but is a problem in places where highly toxic organophosphorus pesticides are available. Medical management is difficult, with case fatality generally more than 15%. However, consensus suggests that early resuscitation with atropine, oxygen, respiratory support, and fluids is needed to improve oxygen delivery to tissues. The role of oximes is not completely clear.

Keywords: Acetyl cholinesterase, atropine, glycopyrrolate, organophosphorus, oximes

Introduction

Pesticide

• Pesticides are chemicals or chemical compounds used to kill various types of pests such as insects, rodents, fungi, and weeds. Pesticides also used to kill various diseases spreading vectors, mosquitos, etc.
• By their nature, pesticides are potentially dangerous to other living beings, including humans, and need to be used with proper safety measures.

Pesticide General Classification

• Insecticides
• Herbicides
• Fungicides
• Rodenticides
• Pediculicides.

• Organophosphates (OPs)
• Carbamates
• Organochlorides
• Pyrethroids
• Neonicotinoids
• Ryanoids [Table 1].

Table 1: Classification of organophosphorus compounds Click here to view

Stages of Toxicity Depending on Time Duration

• Acute cholinergic phase
• Intermediate syndrome
• Delayed polyneuropathy [Table 2].

Table 2: Common toxic syndromes (toxidromes) seen organophosphates poisoning patients Click here to view

Acute Cholinergic Phase

• Starts in minutes, usually within 1 h after ingestion
• It lasts up to 48–72 h
• OPs can produce acute muscarinic, nicotinic, and CNS effects.

Acute Phase: Muscarinic Effects

• Cardiovascular system – bradycardia and hypotension
• Respiratory system – rhinorrhea, bronchorrhea, bronchospasm, cough, and severe respiratory distress (adult respiratory distress syndrome)
• Gastrointestinal (GI) system – increased salivation, nausea and vomiting, abdominal pain, and diarrhea.
• Urinary system – incontinence
• Eyes – blurred vision, miosis (constricted pupil), and increased lacrimation
• Sweat glands – diaphoresis.

Nicotinic Effects

• Fear and emotional lability
• Restlessness, confusion, and coma
• Ataxia, tremors
• Seizures (generalized tonic-clonic seizure)
• Apnea respiratory arrest.

Intermediate Syndrome

• An intermediate syndrome is a delayed onset of muscle weakness and paralysis after OP poisoning. It normally presents after 48 h of OP poisoning (in 20% cases); it may be delayed up to 72–96 h after resolution of the acute cholinergic toxidrome
• Risk factors for the intermediate syndrome are mainly due to exposure to a highly fat-soluble organophosphorus agent due to recirculation of lipid-soluble poison and may be related to inadequate doses of oximes. The intermediate syndrome is not seen in carbamates or nerve gas poisoning
• Muscles involved in intermediate syndrome – ocular muscles (cranial nerves III–VII and X), neck flexor muscles (inability to flex neck), proximal limb muscles with loss of deep tendon reflexes, and respiratory muscles
• Patients also have anxiety, sweating, and cyanosis and may develop a coma
• If muscarinic findings are present, they may respond to an increase in atropine dose.^[5],[6],[7]

Organophosphate Induced Delayed Polyneuropathy

• This occurs after 1–3 weeks of exposure due to degeneration of myelinated nerve fibers
• Clinical features
• Symmetrical, flaccid, distal muscle weakness, and foot drop
• Absent deep tendon reflexes
• Sensory loss – all starts in distal parts of the lower limb, then the upper limb also.^[8],[9]

Organophosphate Poisoning Diagnosis

• Pungent garlic-like smell
• Toxicology analysis for OPs in blood, gastric secretions, and urine
• Serum (or pseudo) cholinesterase levels reduced
• High lactate, low lactate clearance, and low blood pH are poor prognostic factors.

Organophosphate Poisoning Management

• Take care airway, breathing, and circulation
• Correction of oxygenation before the use of atropine is recommended to minimize the potential for dysrhythmias
• Remove the cloths, clean, and wash skin with soap and water. Health care workers must ensure that washing does not delay from other management priorities and should protect themselves from skin contact to poison and contamination
• Gastric lavage (consider gastric lavage for oral poisonings if a presentation is within 1 h of ingestion; if massive ingestion, it may be useful even after this time period) – send the sample for a toxicology screen
• Induction of emesis is contraindicated
• Activated charcoal – 50–100 g initially, followed by 50 g four hourly until charcoal appears in the feces or recovery occurs
• Atropine infusion (atropine reverses ACh-induced bronchospasm, bronchorrhea, bradycardia, and hypotension)
• Atropine competes with ACh at muscarinic receptors present in GI and pulmonary smooth muscle, exocrine glands, heart, and eye, preventing cholinergic activation
• Initial dose 1 mg IV, if no adverse effects give 2 mg every 15 min till the patient develops atropinization (drying of secretions, tachycardia, dry mouth, and dilated pupil)
• Injection (Vial) – 1 mL contains: atropine 1 mg, (ampule – 1 ml = 0.6 mg)
• Atropine also can be used as an infusion (the average patient requires approximately 40 mg/day)
• Monitor the patient – heart rate, pupil size, fasciculations, secretions, and lung crepitation
• The endpoint for atropinization in OP poisoning is dried pulmonary secretions and adequate oxygenation. Tachycardia and pupil changes (mydriasis) must not be used to reduce or to stop subsequent doses of atropine
• Glycopyrrolate is a medication of the muscarinic anticholinergic group. It does not cross the blood–brain barrier and will not produce CNS effects
• This drug is used as an alternative to atropine injections when atropine produces psychological adverse effects
• Injection – each 1 mL contains glycopyrrolate 0.2 mg
• If atropine is not available or avoided because of complications, glycopyrrolate or diphenhydramine may be used as an alternative anticholinergic agent for treating muscarinic toxicity; however, glycopyrrolate will not cross the blood–brain barrier and not useful for the treatment of central effects of OP poisoning. Hence, in patients with CNS symptoms with agitation glycopyrollate with small doses atropine combination can be tried
• Ipratropium bromide nebulization can also be used for muscarinic effects in the lungs
• Oximes – they reactivate phosphorylated AChE. These agents may prevent the aging of AChE and can reverse muscle weakness in OP poisoning. However, it is not useful once the OP compound has aged
• Since atropine does not bind to nicotinic receptors, it may be ineffective in treating neuromuscular dysfunction. Pralidoxime (2-PAM) and other oximes, such as HI-6 and obidoxime, are AChE reactivating agents that are effective in treating both muscarinic and nicotinic symptoms
• 2-PAM should NOT be administered without concurrent atropine to prevent worsening symptoms due to transient oxime-induced AChE inhibition
• 2-PAM 1 g (at least 30 mg/kg in adults and 25 to 50 mg/kg for children in 100 ml normal saline IV over 30 min) eighth hourly for 1^st 24–48 h
• 2-PAM should be administered slowly over 30 min, since rapid administration has occasionally been associated with cardiac arrest, and slow administration prevents the muscle weakness that results from the transient inhibition of AChE as 2-PAM can bind to the enzyme
• After the bolus dose, it appears that superior antidotal effects occur with 2-PAM given as a continuous infusion of at least 8 mg/kg/h in adults and 10–20 mg/kg/h for children
• Severe poisonings may result in prolonged redistribution of toxin; therefore, continuous IV therapy should be adjusted based on the patient's clinical response, and several days of therapy may be required
• Convulsions – treat with benzodiazepine and phenytoin, if severe seizures require muscle relaxants, do not use succinylcholine, which may result in prolonged paralysis
• OP poison-induced seizures should be treated with a benzodiazepine. Prophylactic diazepam injections have been shown to decrease neurocognitive dysfunction after OP poisoning
• Support respiratory failure with mechanical ventilation
• Avoid the use of succinylcholine during rapid sequence intubation in patients with OP poisoning. Succinylcholine is metabolized by AChE (which is inhibited by OP compounds) leading to exaggerated and prolonged neuromuscular blockade in OP poisoned patients. Nondepolarizing neuromuscular blocking agents (e.g. rocuronium) can be used in OP-poisoned patients but may be less effective at standard doses due to competitive inhibition at the neuromuscular junction. Therefore, higher doses will likely be needed.

Carbamate Poisoning

• Carbamates are commonly used as insecticides. Carbamate insecticides are associated with similar toxicities of OP compounds^[10]
• Carbamate compounds: aldicarb, carbofuran, and methomyl
• They are very short acting (half-life is only 30–40 min): carbamates are rapidly absorbed via all routes of exposure. Unlike OPs, these agents are transient cholinesterase inhibitors, which spontaneously hydrolyze from the cholinesterase enzymatic site within 48 h. OPs, however, can irreversibly bind to cholinesterase. Carbamate toxicity tends to be of shorter duration than that caused by equivalent doses of OPs
• Their clinical features are the same as OPs but less severe and short acting
• They reversibly inactivate AChE
• They can also produce pancreatitis
• Treatment – atropine infusion
• Unlike OPs, carbamate intoxications do not irreversibly inhibit cholinesterase, and thus, 2-PAM is not usually required and may worsen symptoms.

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