Poisoning is one of the most common medical presentations to hospital in the UK, accounting for more than 500,000 NHS hospital bed-days in 2007/8.1
Most patients are assessed in emergency departments but occasionally they may present to their GP.
Poisoning may be deliberate or accidental and can occur via oral ingestion, injection, inhalation or topical absorption. The number of potential poisons a patient may have been exposed to is endless.
It includes pharmaceutical agents, illegal or legal 'street' drugs, toxic plants, agricultural chemicals, venomous snakes and industrial solvents.
The answer to the question of whether a patient should be referred for further medical assessment, observation and treatment cannot be answered here but consideration of several factors will help guide clinical judgment.
History
Several points should be elicited from the history, including a list of exactly what has been taken (if known) and when. Poisons may have predictable toxicities that can be anticipated, treated or even prevented.
The physiological effects of polyagent poisoning can be unpredictable. Staggered overdoses may cause toxicity for a prolonged period with increased risk of end-organ damage.
The preparation type is important to identify because sustained release preparations ingested in overdose may cause patients who are initially asymptomatic to deteriorate later.
Knowing the total quantity ingested and the patient's weight enables the dose per kilogram to be calculated, which helps to predict the likelihood of toxicity. Doses likely to cause toxicity can be found on Toxbase (see resources).
Malnourished patients are at increased risk of toxicity. If a patient has vomited since the overdose they may have seen poison in the vomitus. This can be unreliable and should not be used in the clinical interpretation of reduced absorption.
Alcohol consumption at the time of poisoning may make the history unreliable but it is important to note whether it has occurred and, if so, how much alcohol was consumed.
Knowing what regular prescription and OTC medications a patient is on is important. Certain hepatic enzyme-inducing drugs (including carbamazepine, phenytoin, rifampicin and St John's wort) may alter drug toxicities.
Young and old patients and those with pre-existing renal and hepatic impairment have reduced physiological reserve. As a result, they are less able to metabolise and/or excrete toxins and may suffer prolonged toxicity or toxicity at lower doses.
Establish if the patient is pregnant. If unsure, perform a urinary beta-hCG pregnancy test. If pregnant, advice from the UK Teratology Information Service should be sought. All pregnant poisoned patients should be discussed with an obstetrician.
History taking should then focus on the specific symptoms that may indicate that toxicity is occurring and these depend on the poison(s) ingested.
Examination
Physical assessment begins with a review of the patient's airway, breathing, circulation and conscious level. Particular attention should be paid to the respiratory rate. Certain poisons act centrally to increase or decrease respiratory drive.
If available, transcutaneous oxygen saturations should be measured and hypoxia treated with oxygen therapy. If unable to measure this and if concerned, supplemental oxygen should be provided. The heart rate and BP may also indicate end-organ toxicity is occurring. Pyrexia may occur in overdose and temperature should be measured.
Any derangement of physiological parameters should prompt urgent referral to secondary care. Other specific signs may be elicited depending on the poison(s) ingested.
Capillary blood glucose measurement should be performed and corrected if abnormal.
Further advice
Once assessment is complete, consult Toxbase, the online clinical toxicology database of the National Poisons Information Service (NPIS).
This is free to all registered NHS workers and allows rapid access to key clinical information on approximately 14,000 products, as well as potentially hazardous doses and specific management points.
Further advice can be sought from the on-call medical team in secondary care and a 24-hour NPIS telephone helpline is available (see resources).
Sometimes diagnostic tests, such as urgent blood tests, arterial blood gas analysis and ECG, are required even in asymptomatic patients and thus referral must be made nonetheless.
If referral is not required, good safety netting practice should include that a patient remains in a place of safety with a responsible adult who can observe their condition. Provide advice on what to do if the condition worsens.
Psychiatric assessment
Following deliberate overdose, patients in secondary care will undergo psychiatric assessment. In primary care, if referral to hospital is not required, psychiatric assessment must still be performed and should include an assessment of the ongoing risk of self-harm.
This may require discussion with the on-call psychiatry team.
Immediate management in primary care
If available, oxygen should be given for proven or suspected hypoxia. Conscious hypoglycaemia can be corrected by sugary drinks and foods followed by a longer-acting carbohydrate to prevent recurrence.
Many drugs will bind to activated charcoal (50-100g, orally), which reduces absorption into the circulation. This is indicated if the time since ingestion is less than one to two hours, but can be longer if the drug delays gastric emptying or is a sustained release preparation.
A protected airway is required. Certain drugs will not bind to activated charcoal; commonly ingested examples include cyanide, ethanol, heavy metals, iron, lithium and methanol.
Naloxone (0.4-2mg) is a rapid-onset (IV faster than IM) short-acting opiate antagonist, which can be used in the reversal of opiate overdose.
Chronic carbon monoxide poisoning
Carbon monoxide is a colourless, odourless and tasteless gas produced by the incomplete combustion of carbon-based fuels. Haemaglobin has an affinity for carbon monoxide 200 times that of its affinity for oxygen, forming carboxyhaemoglobin.
The consequent reduction in effective oxygen carriage capacity of the blood causes tissue hypoxia. As cellular respiration continues, tissue anoxia ensues with subsequent end-organ damage. Carbon monoxide poisoning is described as acute or chronic.
Symptoms of chronic (persistent and long-term) exposure to low levels of carbon monoxide are mainly caused by faulty domestic boilers.
Symptoms are often vague and non-specific and one should always consider chronic carbon monoxide poisoning as a differential diagnosis when met with any of the following: headaches, nausea, dizziness, light-headedness, fatigue and listlessness, difficulty concentrating, cognitive decline, alteration of affect and changes in personality.
It may also exacerbate pre-existing cardiovascular symptoms. There may be a history of symptoms worsening during the colder months when boilers and fires are being used more, or of symptoms improving when away from the home.
When suspected, immediate advice should be to not return to the potential source until a qualified engineer who is Gas Safe registered has serviced all possible causative appliances.
Typically, upon removal of the source, symptoms mostly resolve unless there has been an episode of acute poisoning. The patient should be advised not to smoke as carbon monoxide is contained in tobacco smoke.
Follow-up should be arranged for symptom review to ensure resolution.
Reflect on this article and add notes to your CPD Organiser on MIMS Learning
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Reference
1. Health Protection Agency.National Poisons Information Service - Annual Report 2008/9. London: Stationary Office, 2009. www.hpa.org.uk/web/HPAwebFile/HPAweb_C/1252326271299
Resources
1. Toxbase. www.toxbase.org 24-hour helpline 0844 892 0111.
2. United Kingdom Teratology Information Service (UKTIS). www.uktis.org Telephone: 0844 892 0909.
- Dr Goddard is a specialty registrar in acute medicine and general (internal) medicine at the Western General Hospital, Edinburgh, and Dr Dear is a consultant in clinical pharmacology and general (internal) medicine at the Royal Infirmary of Edinburgh.
