Journal scan: Elsevier’s Medicine, Current Issue, Volume 52 Issue 6, June 2024, Seminar on Poisoning

From the desk of the Editor-in-Chief

Abstracts

General aspects of poisoning

Epidemiology of poisoning

Accidental poisoning is most common in children, but deliberate self-harm becomes predominant in teenagers and early adulthood. The epidemiology of poisoning can be studied using mortality data, hospital admission rates and enquiries to poisons information services. Effective strategies for preventing suicide and reducing the risk of accidental poisoning require an understanding of the epidemiology of poisoning.

Principles of assessment and diagnosis of the poisoned patient

Assessment of patients with acute poisoning includes history-taking, assessment of airway, breathing, circulation and consciousness level, physical examination to elicit relevant clinical signs and appropriate investigations. Diagnosis is usually based on the history, recognition of toxidromes

Principles of management of the poisoned patient

One of the fundamental complications within toxicology is that patients may not know or disclose what they have been poisoned with. Consequently, a sound and considered general approach to identify potential harms and plan clinical management is necessary. This chapter aims to guide the reader through the initial approach and general principles to consider when managing a poisoned patient.

Cardiovascular complications of poisoning

Cardiovascular complications are common in poisoned individuals and require prompt attention and intervention. The pathophysiology of the cardiovascular complications depends on the substances involved, which are often unknown. An initial assessment and investigations are key to detecting cardiac disturbances and their cause. Arrhythmias resulting from poisoning in the form of tachycardias and bradycardias are relatively common with some substances such as sympathomimetics or β-adrenoceptor blockers. Changes in electrocardiogram intervals are also common manifestations, not only because of the action of these substances, but also secondary to disturbances of pH or electrolytes. Here we describe an approach to managing patients with exposure to cardiovascular poisoning including clinical assessment, investigations and management.

Metabolic complications of poisoning

Poisoning caused by a large range of drugs and chemicals can induce metabolic complications via many different mechanisms. Some metabolic complications are life-threatening but all require careful assessment, appropriate monitoring and consideration of treatment. Prompt diagnosis and management reduce morbidity and mortality. Treatment may be targeted to the specific poisoning, and can be time-critical, or can follow approaches similar to those of general and acute medicine. This review introduces metabolic complications associated with sodium, potassium, metabolic acidosis, rhabdomyolysis and methaemoglobinaemia.

Psychiatric assessment of self-poisoning

Self-poisoning accounts for a significant number of attendances to acute services. It can occur at any age. The reasons that lead someone to self-poison are variable and individual. It is often a manifestation of distress. Women are more likely to present, or die, after overdose than men, although men are more likely to die by suicide overall. Self-harm, including self-poisoning, is a strong risk factor and antecedent to suicide. Psychosocial assessment offers an important opportunity to intervene and should be undertaken by a clinician with appropriate training; this should be collaborative where possible and lead to the identification and formulation of relevant risk factors to guide management. The UK National Institute for Health and Care Excellence advises against the use of risk assessment tools and scales and risk stratification, and recommends that the focus of the assessment should be on the person’s needs and how to support their immediate and long-term psychological and physical safety.

Drug misuse

While the misuse of traditional drugs remains common, the emergence of new psychoactive substances (NPS) has changed the landscape of drug misuse in recent years. Although hundreds of NPS have been identified, opioids, including new synthetic examples, still dominate mortality. The exact substances causing toxicity are often unknown on presentation, and multiple exposures are commonly involved. Management is therefore based on a recognition of the drug group(s) involved by identifying the clinical toxidrome. Depressants, stimulants, hallucinogens, cannabinoids and dissociatives represent the most frequently identified drug toxidromes.

Poisonous substances

Poisoning by alcohols and glycols

Ethanol intoxication was commonly encountered and can cause hypotension, hypoglycaemia, lactic acidosis, seizures and coma. Isopropyl alcohol and its metabolite acetone cause profound depression of the central nervous system with rapid onset. Toxic alcohols include methanol, ethylene glycol and diethylene glycol; these can cause severe metabolic acidosis, acute renal failure and, for methanol, severe visual disturbance. Toxicity is attributable to metabolites and there is a characteristic delay between ingestion and the occurrence of severe toxicity. Assessment of the extent of exposure requires laboratory confirmation of toxic alcohol concentrations, which conventionally involves specialized laboratory assays that are not always readily available. Management strategies include assessment of toxic alcohol exposure, early administration of fomepizole to prevent formation of metabolites and, in patients with established poisoning, haemodialysis to remove metabolites.

Anticoagulants in poisoning

Blood coagulation is the result of a complex cascade of proteases that produce an insoluble fibrin polymer from soluble fibrinogen. Abnormal or excessive coagulation can cause venous thromboembolic disorders or arterial thromboembolic disease. Parenteral and oral anticoagulants have demonstrated efficacy in treating these conditions. Haemorrhage is a predicable consequence of anticoagulant poisoning. Treatment involves the general management of haemorrhage, and the administration of specific antidotes for individual anticoagulants is discussed. Complicated cases should be discussed with a haematologist and the UK National Poisons Information Service.

Anticonvulsant toxicity

Anticonvulsant medications are used in the treatment of epilepsy as neuropathic pain, migraine and psychiatric illness. Anticonvulsants suppress neuronal excitation to reduce the likelihood of seizure activity. Generally, management is supportive, with correction of physiological and metabolic parameters. Drug concentrations can help guide specific treatments such as l-carnitine (for valproate) and multiple-dose activated charcoal (for carbamazepine, phenytoin and phenobarbital). Extracorporeal treatments can be used to enhance elimination.

Poisoning by antidepressants and antipsychotics

Tricyclic antidepressants, citalopram, venlafaxine and monoamine oxidase inhibitors are the most toxic antidepressants in overdose. Features include hypotension and arrhythmias that are best managed by the aggressive correction of metabolic acidosis with sodium bicarbonate. Antipsychotic drugs differ in their chemical structure and specificity at dopamine receptors. Overdose produces a range of adverse effects including sedation and acute extrapyramidal reactions. Cardiovascular effects including hypotension, prolongation of the QT interval and, potentially, arrhythmias including torsade de pointes are also seen.

Poisoning by carbon monoxide

Accidental carbon monoxide (CO) poisoning causes 100 hospital admissions and 7 deaths per million UK population. Toxicity occurs mainly through the formation of carboxyhaemoglobin (COHb), causing ischaemia of vital organs. Features are non-specific and include headache, gastrointestinal upset, dizziness, weakness, convulsions, coma, chest pain and dyspnoea. Neuropsychiatric features can appear up to 40 days after the initial exposure. The diagnosis can be missed unless a history of exposure to sources of CO is elicited or a CO alarm triggered. There may be a history of others (including pets) with a similar illness in a particular location (e.g. home, office) and an improvement in symptoms when away from that location. A COHb concentration >5% in non-smokers, and >10% in smokers, indicates CO poisoning. A COHb concentration >30% indicates severe poisoning, although lower concentrations do not rule out severe CO poisoning. Patients should be treated with high-flow oxygen, which usually results in rapid improvement. Complications, including myocardial infarction and stroke-like features, should be managed conventionally. The source of CO should be identified and eliminated. Patients and families should be educated to prevent CO poisoning in the community.

Poisoning with cardioactive substances

Cardiovascular poisoning may be significant from toxicity related to β-blockers, calcium channel blockers and digoxin. Various treatment options exist that are based on the pharmacological pattern of toxicity from these drugs. These include supportive clinical care and the use of specific antidotes.

Poisoning by household products

Exposures to household products are common. Most of these exposures are accidental, causing minimal symptoms. Serious toxicity is possible if large amounts or high concentrations of products are involved.

Poisoning by metals

Lead can be absorbed after inhalation or ingestion and is toxic to most organ systems. Management involves avoidance of exposure and, in more severe cases, chelation therapy with either sodium calcium edetate or dimercaptosuccinic acid. Iron poisoning causes metabolic effects in proportion to the concentrations of free iron, although individual responses vary. Toxicity is therefore related to the dose ingested. Iron concentrations can rise and fall, making plasma concentrations difficult to interpret in acute poisoning. Clinical features include severe gastrointestinal irritation, cardiovascular collapse and direct organ damage to the liver and kidneys. Unconsciousness occurs in severe cases. The chelating agent desferrioxamine is used as the antidote, although uncertainty remains over the optimal dose in individual patients. Chelating agents are also used in other metal poisonings. It is advised that the investigation and management of suspected heavy metal poisoning should be conducted in consultation with a poison centre and/or a clinical toxicologist.

Poisoning by paracetamol

Paracetamol overdose is common. If left untreated, liver and/or renal failure can develop. Administration of the antidote, acetylcysteine, within 8–10 hr of overdose minimizes or prevents liver damage. After overdose, the tests used to identify that patients are at risk of liver injury are well established but have limitations. Once liver injury has occurred, important prognostic factors are the presence of hepatic encephalopathy, the international normalized ratio, acid–base status and renal function. The only treatment for acute liver failure is transplantation.

Poisoning by opioids

Opioids are among the most commonly prescribed analgesic medications, and opioid toxicity is becoming an increasing problem across the world. Patients typically present with a triad of signs: reduced consciousness, miosis and a reduced respiratory rate with shallow breaths. Patients with significant opioid toxicity are at risk of airway compromise, and basic supportive measures should be performed. Naloxone is a non-selective μ-opioid receptor antagonist that competitively binds to the μ-opioid receptor and should be administered, ideally intravenously, to patients with significant opioid toxicity.

Poisoning by pesticides

Around 150,000 people die each year from pesticide poisoning. Most deaths result from self-poisoning by ingestion, rather than occupational or accidental exposures, which are typically topical or inhalational. Severe pesticide poisoning is more common in rural lower- and middle-income countries where pesticides are widely used in smallholder agricultural practice and therefore freely available. Significant acute poisoning is much less common in industrialized countries; here the long-term effects of low-dose chronic exposure most concern the population. Poisoning from organophosphorus and carbamate insecticides causes most severe cases and deaths worldwide, although numbers are falling as the most highly toxic compounds are withdrawn from agricultural practice. Severe organophosphorus poisoning requires urgent resuscitation and administration of oxygen, atropine and oximes. Paraquat and aluminium phosphide are major problems in some countries, with case fatality usually >50% and no effective treatments. Newer pesticides that have become widely used over the last 30 years, for example neonicotinoid and phenylpyrazole insecticides, are more selective in their toxicity to pests, resulting in far less acute human toxicity and few deaths. Toxicity can result from solvents rather than the pesticide’s active ingredient. Acute poisoning with newer pesticides usually requires only careful supportive care.

Poisoning by toxic plants and fungi

Poisoning by toxic plants or fungi is not uncommon in the UK. The identity of the suspected toxin is frequently unknown to the patient. Clinicians must be aware of the toxicology, clinical features and treatment of serious and common poisonings to effectively manage such cases.

Poisoning by venomous animals

Poisoning by venomous creatures is common. Most is benign, causing only minor irritation or pain, but rarely significant morbidity and mortality can occur. Medically important venomous creatures include snakes, spiders, scorpions and marine creatures. For suspected cases of severe envenoming, seek early expert advice from a clinical toxicologist or poisons information centre. First aid measures include pressure bandaging of the affected limb with immobilization in suspected snakebite and funnel web spider bite, and hot water immersion therapy for many marine stings. Management of severe envenoming requires resuscitation with early provision of antivenom where available. Ensure the patient has adequate tetanus prophylaxis. Pain is often prominent and adequate analgesia should be provided. Primary prevention of bites and stings is crucial to reduce the impact of envenoming.

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