poisining

poisoning
acute poisoning is one of the most common medical emergencies, accounting for 10-20% of all acute medical admissions. at least 50% involve more than one drug, with alcohol being the most frequent second agent.
general approach to the poisoned patient
taking a history
in most cases, the diagnosis of poisoning is apparent on the basis of the history.
benefits from history taking include the following :
1- the amount and type of substance that has been taken is recorded.
2- the timing of ingestion or exposure.
3- establishing whether the drugs belonged to the patient, or to a friend or relative, and the source of the drug (i.e. over the counter, prescription, street) which is important in the prevention of future poisoning.
4- the nature of any drug taken which can be identified from descriptions of the tablets or remaining pills, packets or bottles.
5- the reasons for taking the drug which often include relationship difficulties, work- or school-related difficulties, drug addiction, psychiatric illness or bereavement.
6- details of the past medical history, particularly a history of asthma, jaundice, drug misuse (and by which routes), head injury, epilepsy, cardiovascular problems, previous psychiatric illness and self-harm should be taken.
limitations of history taking
1- information may not always be forthcoming, either because patients do not know what has been taken or because they may have been under the influence of alcohol or the drug itself at the time of ingestion.
2- a few patients deliberately mislead doctors but this is very rare, with the exception of drug misusers.
clinical features of poisoning
first ensure that:
1- the airway is clear
2- the patient is breathing adequately
3- the circulation is not compromised.
if the patient is alert and has a stable circulation, proceed to examination. the only exception is where immediate eye or skin decontamination is required. a standard clinical examination should be carried out on every poisoned patient. needle marks or previous evidence of self-harm, e.g. razor marks on forearms, should be sought. examination findings such as pupil size, respiratory rate and heart rate may support the diagnosis in an unconscious patient, but on their own merely help to narrow down the potential list of toxins.

*** clinical signs that can help identify which toxin has been taken***
1- pupil size : small in opioids, clonidine - large in tircyclic antidepressents, alcohol, amphetamines, cocaine, antihistamines.
2- cerebeller signs in anticonvulsants, alcohol.
3- extrapyramidal signs in phenothiazines, haloperidol, metochlopromide.
4- respiratory rate : increased in salicylates - reduced in opioids, benzodiazepines
5- cyanosis any cns depressent drug or agent causing methaemoglobinaemia eg. dapsone
6- blood pressure : hypotension in tircyclic antidepressents, haloperidol. hypertension in cocaine, a-adrenoceptor agonist.
7- heart rate : tachycardia or tachyarrhythmias in tircyclic antidepressents, theophylline, digoxine, antihistamines. bradycardia or bradyarrhytmias in digoxine, b- blockers, ca- channel blockers, opioids.
8- right upper quadernt/ renal angle tenderness : in paracetamol hepatotoxicity and renal toxicity.
9- needles tracks in opioids and other misuse drugs.
10- epigastric tenderness in nsaids and salicylates.
11- body temp. hyperthermia and sweating in ecstasy, serotonine re-uptake inhibitors. salicylates. hypothermia in any cns depressent drug eg. opioids, chlorpromazine.
12- rhabdomyolysis : eg. amphetamines, caffeine.
role of the toxicology laboratory
in most patients the diagnosis of poisoning is made on the history and clinical signs alone. in some cases, such as poisoning with paracetamol, aspirin or iron, subsequent management of the patient depends on measurement of the amount of toxin in the blood.
in unconscious patients, a qualitative screen of the urine (e.g. urine immunofluorescence drugs of misuse screening test) is an effective way to confirm recent use of drugs such as benzodiazepines, cocaine, ecstasy, opioids and cannabis.
general management of the poisoned patient
general management of the poisoned patient is directed to prevent absorption or enhancing elemination and depend on the routes of exposure to the toxins.
preventing absorption
1- direct eye contact - eye irrigation >> wash eyes thoroughly for at least 15 min with normal saline or water. remove particles from palpebral fissures, if pain persists, flourescein dropings and slit lamp examination for corneal damage.
2- inhalation oxygen and brochodilator >>> give high flow o2, 12l/min. nebulised b2-adrenoceptors agonist if patient is wheezy.
3- ingestion - a- gastric lavage >>> only if a potentially life-threatening amount of toxin has been ingested within the last hour. not to be used for acids, alkalis, or petroleum distillates.
b- activated charcoal >>> 50 g can be given orally to an adult if a potentially toxic amount of toxin has been ingested within the last hour, but only if the toxin is absorbed by the charcoal. activated charcoal is the most common method used to prevent drug absorption and is given orally as black slurry owing to its large surface area and porous structure, this is highly effective in adsorbing most toxins. there are a few agents that do not bind to activated charcoal.
substances poorly adsorbed by activated charcoal
acids, alkalis, ethanol, ethylene glycol, iron, lithium, mercury, methanol

activated charcoal should not be mixed with ice cream or flavouring agents as these reduce its adsorptive capacity. in patients who cannot swallow or who have a reduced level of consciousness, the activated charcoal should be given via a nasogastric tube. in all cases, the airway must be adequately protected to avoid aspiration pneumonitis.
multiple doses of activated charcoal can be given ( 50 g every 4 hours) in poisoning by carbamazepines, dapsone, quinine and theophylline. in such circumstances it is important that a laxative, such as sorbitol is given to avoid obstruction due to charcoal briquette formation in the gastrointestinal tract.
c- whole bowel irrigation >>> polyethylene glycol solution is given for potentially toxic ingestion of iron, lithium and theophylline. whole bowel irrigation is performed by asking patients to drink 1 litre of polyethylene glycol every hour until their rectal effluent is clear. such preparations are not associated with osmotic changes. contraindications include inadequate airway protection, haemodynamic instability, gastrointestinal haemorrhage, obstruction or ileus. whole bowel irrigation may precipitate nausea and vomiting, abdominal pain and electrolyte disturbances.

4- inoculation/direct skin contact removal of clothing / skin washing >>> wash with copious amounts of soap and water for chemical and pesticide exposures.



enhancing elemination
if the poison despite these measures reach the blood then the general measures include
1- urinary alkalinisation >>> enhances elimination of salicylates and some pesticides. give 1 liter of 1.26% sodium bicarbonate iv over 3 hours. it is also sometimes used for poisoning with methotrexate. complications include alkalaemia, hypokalaemia and occasionally alkalotic tetany. hypocalcaemia may occur but is rare.
2- extracorporeal methods of elimination eg. haemodialysis or haemoperfusion >>> for serious poisoning with salicylates, theophylline, ethylene glycol, methanol, and carbamazepine.
3- lipid emulsion therapy : lipid emulsion therapy, or ‘lipid rescue’, is being used increasingly for the management of poisoning with lipid-soluble agents, such as local anaesthetics, tricyclic antidepressants, calcium channel blockers and lipid soluble ?-blockers such as propranolol. it involves intravenous infusion of 20% lipid emulsion (e.g. intralipid ®) until there is clinical improvement. it is thought that lipid-soluble toxins partition into the intravenous lipid, reducing target tissue concentrations. the elevated myocardial concentration of free fatty acid induced by intralipid administration may also have beneficial effects on myocardial metabolism and performance by counteracting the inhibition of myocardial fatty acid oxidation produced by local anaesthetics and some other cardiotoxins.
in the seriously poisoned patient, supportive care, including the treatment of seizures, coma and cardiovascular complications, is critical to good outcome. seizures are seen most commonly in poisoning by theophyllines, non-steroidal anti-inflammatory drugs (nsaids) and tricyclic antidepressants, and are best treated by airway management and i.v. diazepam (10 mg for an adult, repeated as necessary). ventilatory support may be required until consciousness returns, and complications such as aspiration pneumonia should be treated promptly. patients must be observed closely for signs of deterioration whilst the effects of the toxin they have taken wear off.
ipecacuanha administration is no longer recommended in the management of the poisoned patient.
****despite popular misconceptions, specific antidotes are only available for a small number of poisons.
antidotes available for the treatment of specific poisonings
1-anticoagulants (e.g. warfarin, rodenticides) >>> vitamin k, fresh frozen plasma
2- ?-adrenoceptor antagonists (?-blockers) >>> i.v. glucagon, adrenaline (epinephrine)
3- calcium channel blockers >>> calcium gluconate, calcium chloride, glucagon
4- cyanide >>> oxygen, dicobalt edetate, nitrites, sodium thiosulphate, hydroxocobalamin
5- ethylene glycol/methanol >>> ethanol, 4-methylpyrazole
6- iron salts >>> desferrioxamine
7- opioids >>> naloxone
8- organophosphorus insecticides >>> atropine, oximes (pralidoxime, obidoxime salts
9- paracetamol >>> n-acetylcysteine, methionine
10- cardiac glycosides, e.g. foxglove, digoxin >>> digoxin-specific antibody fragments

substances of low toxicity
every substance, even water, is a potential toxin, but the dose is critical in predicting risk of toxicity. for practical purposes, some substances can be ingested by humans in large amounts without serious sequelae.
substances of very low toxicity
1- most antibiotics but tetracyclines and antituberculous drugs are toxic
2- anti-ulcer drugs: h2-blockers or proton pump inhibitors
3- chalk. 4- paper glues and wallpaper paste. 5- household plants
6- washing-up liquid but dishwasher tablets are highly corrosive
7-oral contraceptive pills. 8- lead pencils and felt-tip pens
9- silica gel. 10- emollient and zinc oxide creams