Poisoning and envenomation

5.3 Poisoning and envenomation



James Tibballs, Ed Oakley, Ken Winkel


Poisoning and envenomation are two important areas of emergency care that should be familiar to any health practitioner involved with acute care of children and young people.



Poisoning


Poisoning is a common health problem among children. It is responsible for numerous attendances to emergency departments of children’s hospitals. Over 3500 children aged 0–4 years are admitted annually to Australian hospitals as a result of poisoning incidents. Worldwide, poisoning is the third most common cause of death among young children. A great deal of effort is expended upon a problem that is largely preventable. A Poisons Information Centre serving a population of 5 million receives approximately 40 000–50 000 telephone enquiries per annum; two-thirds concern actual poisoning and, of those, 60–70% concern children aged 4 years and younger.



Epidemiology


The nature of poisoning varies for different age groups in children. Although poisoning in childhood is usually unintentional, the possibility of deliberate poisoning in the younger child as part of child abuse should not be forgotten. Pharmaceutical substances are involved in 70% of poisonings. In hospitals, errors in drug administration are frequent causes of poisoning.



Newborns


Poisoning is almost always iatrogenic in this age group. For example, newborns are at risk at delivery, when they may be given ergometrine instead of vitamin K, causing severe hypertension, convulsions and coagulopathy. In intensive care units, the frequent use of potent cardiovascular drugs, gentamicin, barbiturates, phenytoin, theophylline, digoxin, furosemide and opiates predispose the infant to poisoning.


It is not acceptable to perform noxious procedures without analgesia and sedation, and it is commendable that opiates are used in the newborn, but great care should be taken to ensure that overdose does not cause cardiorespiratory failure. Repeated doses or infusions of opiates should be confined to newborns who are mechanically ventilated, and, wherever possible, local or regional anaesthesia should be employed for surgical procedures. Local anaesthetic agents or opiates administered to the mother during labour may poison the newborn.


Care should be exercised with the use of topical antiseptics. Mercurochrome, commonly applied to the umbilical stump, may cause mercury poisoning if used in excess. Hexachlorophene should not be used as a regular bathing solution because it is readily absorbed percutaneously, causing neurotoxicity. If used in excess, iodinated compounds may cause hypothyroidism. Occasionally, mistakes in the preparation of artificial foods may cause serum electrolyte disorders and dehydration.



Age 1–5 years


Poisoning occurs most frequently in this age group. Most instances are said to be accidental, in which the young child discovers a drug or a household cleaning or chemical agent. The majority of serious poisonings occur with prescribed drugs or with over-the-counter drugs. Parents are often unaware that drugs must be stored safely and they underestimate the capabilities of young children who, at this age, become increasingly mobile and curious. They eat substances that are not palatable to adults, and tablets and capsules that resemble lollies (sweets).


The incidence and severity of accidental poisoning from drugs has been reduced markedly by the use of blister packs and containers with child-resistant lids. Poisoning in the home often occurs between 10 am and noon or between 6 pm and 8 pm when the child is active or hungry and when supervision has lapsed because the parent is involved in other household activities.



Age 6–12 years


Poisoning is relatively uncommon in this age group but it may be truly accidental, such as drinking a poison from a bottle that has been labelled wrongly, or when toxic agents have been stored inappropriately. A common example is storage of potentially toxic liquids in soft-drink containers in garden sheds. Although uncommon, deliberate self-poisoning in this age group may occur as drug abuse or manipulative behaviour, or, less commonly still, genuine suicidal intent.



Age 13–17 years


Emotionally disturbed adolescents and young adults may poison themselves deliberately, usually by ingestion, to manipulate their environment, or they may harbour a genuine suicidal intent. They may seek the thrill of drug abuse by inhalation or injection, sometimes as group behaviour. The peak incidence of teenage poisoning is at 14–16 years of age. Repeated episodes occur more frequently among girls but boys’ suicide attempts tend to be more successful.



Management


The immediate aim in the management of poisoning, whether serious or not, is to attend to the effects of the poison on the patient. Later, attention should be given to the circumstances with the aim of preventing a recurrence. There are innumerable poisons. All medicines and many household substances are poisonous if taken in sufficient quantity. Upon presentation, the action to be taken, if any, will be determined by the substance involved, its amount, the interval between ingestion and presentation, and the effect of the poison. The following principles of management may be applied universally.


In adolescents with intentional ingestions all medications should be removed from their person on arrival at hospital to prevent further ingestion.



Support vital functions


It is imperative to maintain and support vital functions if these are depressed. Many poisons are excreted adequately or metabolized by the body if the vital functions are maintained. If the patient is unconscious, the airway, the depth and frequency of breathing, and the circulation should be examined for adequacy. Chapter 5.2 provides a full discussion on the management of deficiencies of the airway, breathing and circulation.


Loss of consciousness due to poisoning may be associated with cardiorespiratory failure and require endotracheal intubation and mechanical ventilation, preferably given by experienced personnel.



Establish the diagnosis


It is important to establish:



• what poisons are involved


• in what quantity


• when exposure occurred.


Often the diagnosis of poisoning is self-evident, but at times the diagnosis is not obvious. When a poison has been identified, it should never be assumed that other poisons could not be involved. The symptoms and signs of poisoning are diverse but dangerous drugs threaten vital functions. Seriously poisoned patients present commonly with:



• unconsciousness


• cardiorespiratory failure


• convulsions.


If any of these are present and the cause is otherwise not known, poisoning should be high on the list of differential diagnoses. A meticulous physical examination and history provides invaluable help in diagnosis and treatment. Laboratory investigations may be necessary to establish a diagnosis, determine the amount of poison in the body, and help determine specific treatment for certain poisons.



Prevent absorption


Some poisons contaminate the skin, conjunctivae and mucous membranes, and other poisons are inhaled as gases. Surface contamination requires copious irrigation with water, whereas inhalational poisoning may require oxygen therapy and mechanical ventilation. The great majority of poisons are ingested, for which the options for therapy include induced emesis (rarely), oral or gastric administration of activated charcoal, gastric lavage and whole bowel irrigation. If the poison has been absorbed already and has reached the vascular compartment, invasive techniques such as the following may be required:



• plasmafiltration


• haemofiltration


• charcoal haemoperfusion


• haemodialysis


• peritoneal dialysis


• exchange transfusion.


The poison, its amount and the seriousness of its effects determine the treatment of the poisoned patient. These must be weighed against the hazards of removal. Unconscious or drowsy patients, or patients who cannot protect their own airway, should not undergo induced emesis or gastric lavage or be given activated charcoal or colonic washout solutions. The consequences of aspirating gastric contents during vomiting or regurgitation in a less than fully conscious state far outweigh the dangers of many untreated poisons, as the mortality rate from severe pneumonitis is approximately 50%. However, it is appropriate to remove a wide variety of ingested poisons with either:



• activated charcoal


• whole bowel irrigation


• gastric lavage, or


• a combination of these techniques.


Circumstances of presentation and ingestion dictate the choice of technique.


Induced emesis, using ipecacuanha, was a commonly applied form of therapy but has now been largely abandoned because of limited effectiveness, the development of more effective techniques (e.g. activated charcoal) and risk of aspiration of gastric contents.


Activated charcoal is probably the most appropriate therapy in the emergency department, although whole bowel irrigation may be preferable for some agents. Gastric lavage should be reserved for a recent (within 1 hour) serious life-threatening ingestion in a conscious patient or for serious poisoning in a less than fully conscious patient who has airway protection. It is preferable that all patients undergoing gastric lavage have the airway protected with endotracheal intubation. The circumstances for the employment of each technique are summarized in Figure 5.3.1.


image

Fig. 5.3.1 Management of poisoning.



Activated charcoal


Activated charcoal is itself not absorbable but it adsorbs many different poisons in the gastrointestinal tract and thus prevents absorption of poison into the circulation. However, activated charcoal does not adsorb some poisons, including some elemental metals, some pesticides, ferrous sulphate, ethanol, corrosives and petrochemicals. There are many different preparations of activated charcoal, some with sorbitol as a laxative, but with these excessive diarrhoea and hypernatraemic dehydration may result.


To be effective, activated charcoal should be administered within 1 hour of ingestion by mouth or by a nasogastric tube in a fully conscious patient, or by gastric tube in a less than fully conscious patient after the airway has been secured with an endotracheal tube. Children may be more likely to drink it if it is cooled and offered in an opaque paper cup with a lid and a black straw. The dose of activated charcoal is 10 times the ingested poison by weight or 1–2 g/kg of the child’s body weight. Continued or repeated doses of activated charcoal, at doses of 0.25 g/kg 4–6-hourly, are useful if the poison is in a sustained-release preparation or if the charcoal is known to increase the total body clearance of the poison by interruption of its enterohepatic circulation or by leaching it from the circulation of the gastrointestinal mucosa. An alternative dosage regimen is 0.25 g/kg hourly for 12–24 hours. Activated charcoal should not be administered if gastrointestinal ileus is present, as this may cause regurgitation. Aspiration of activated charcoal may have a fatal outcome.


Activated charcoal is often administered, probably unnecessarily, with a laxative, notably magnesium sulphate, to prevent constipation. If magnesium sulphate is used, care should be taken to avoid hypermagnesaemia, a potential risk with repeated doses. Activated charcoal does not adsorb ipecacuanha and thus there is nothing to be gained by administering it to the patient whose induced emesis is excessive.



Gastric lavage


Gastric lavage was a commonly applied form of therapy but has now been largely abandoned. It is an invasive procedure and is justified only for significant recent poisoning when other techniques are contraindicated or are unreliable. It may also be indicated when the poison delays gastric emptying or forms concretions in the stomach. To be effective, however, it must be performed well and care must be taken to prevent complications. It is preferable to protect the airway with endotracheal intubation in all patients. Endotracheal intubation should be performed only by a person experienced in rapid sequence intubation and resuscitation.


Gastric lavage should not be performed after the ingestion of a corrosive substance because additional damage to the oesophagus (perforation, mediastinitis) and stomach (perforation) may occur. It is also unwise to perform gastric lavage after ingestion of petrochemicals or hydrocarbons as these substances have a very low surface tension and cause severe pneumonitis, even after minor contamination of the oropharynx, which may occur after the passage of the lavage tube renders the gastro-oesophageal sphincter incompetent. The risk of causing or exacerbating chemical pneumonitis exceeds the benefit of poison removal, despite the depression of central nervous system function that may follow. Such patients recover if vital functions are preserved.


Gastric lavage is a potentially traumatic procedure, particularly to the oropharynx, even when indicated. Occasionally the oesophagus and stomach have been perforated. It is psychologically as well as physically traumatic. For physical safety, the child must be restrained: this is best achieved by wrapping the child in a sheet with the arms pinned by the side. The child must be held in a lateral head-down position. For gastric lavage to be performed well, safely and atraumatically, it should be preceded by induction of general anaesthesia with endotracheal intubation.



Whole bowel irrigation


This is an effective technique to limit absorption of a poison. It is the preferred technique when the poison has passed beyond the pylorus and therefore cannot be removed by gastric lavage and when the substance is a drug or substance not adsorbed by activated charcoal. Slow-release drug preparations may also be removed with this technique.


The agent used is a mixture of polyethylene glycol and electrolytes that flushes out the contents of the bowel without disturbing the serum volume, osmolality or electrolytes. It is administered via nasogastric tube at a rate of 30 mL per kg per h for 4–8 hours until the rectal effluent is clear. It should not be administered to a less than fully conscious patient or when gastrointestinal ileus is present. Concomitant administration of activated charcoal is counterproductive.



Removal from the circulation


If the poison reaches the circulation, an invasive extracorporeal technique may be necessary to achieve removal. Usual techniques include forced diuresis, haemodialysis, plasmapheresis and charcoal haemoperfusion. These techniques are usually reserved for recognized circumstances when there is deterioration of vital functions despite maximal therapy (mechanical ventilation, inotropic/vasopressor therapy and artificial renal therapy) or the lack or failure of an adequate excretory or metabolic pathway (renal, hepatic) to eliminate the poison. For these techniques to be effective, however, the poison must have a relatively small volume of distribution. Peritoneal dialysis is not an efficient technique to remove poisons from the blood. Occasionally, the small size of a patient and the properties of a poison permit its removal by exchange blood transfusion.



Administer an antidote


Only relatively few poisons have antidotes, but knowledge and use of these can be life-saving. The appropriate dose of each is determined by the amount of poison and its effects. A list of common important antidotes is given in Table 5.3.1.


Table 5.3.1 Antidotes to some serious poisons



















































































Poison Antidotes Comments
Amphetamines Esmolol i.v. 500 μg/kg over 1 min, then 25–200 μg/kg/min
Labetalol i.v. 0.15–0.3 mg/kg or phentolamine i.v. 0.05–0.1 mg/kg every 10 min
Diazepam 0.2 mg/kg i.v.		 Treatment for tachyarrhythmia
Treatment for hypertension
Controls agitation, aggression
Benzodiazepines Flumazenil i.v. 3–10 μg/kg, repeat 1 min, then 3–10 μg/kg/h Specific receptor antagonist
Beta-blockers Glucagon i.v. 140 μg/kg, then 0.2–1 μg/kg/min
Isoprenaline i.v. 0.05–3 mg/kg/min
Noradrenaline (norepinephrine) i.v. 0.05–1 μg/kg/min		 Stimulates non-catecholamine cAMP, preferred antidote
Beware hypotension
Calcium channel blocker Calcium chloride i.v. 10%, 0.2 mL/kg  
Carbon monoxide Oxygen 100% Decreases carboxyhaemoglobin.
May need hyperbaric oxygen
Cyanide Dicobalt edetate i.v. 7.5 μg/kg (max 300 mg) over 1 min, then 300 mg at 5 min
Sodium nitrite 3% i.v. 0.33 mL/kg over 4 min, then sodium thiosulphate 25% i.v. 1.65 mL/kg (max 50 mL) at 3–5 min		 Give 50 mL 50% glucose after each dose
Nitrites form methaemoglobin–cyanide complex. Beware excess methaemoglobin > 20%
Thiosulphate forms non-toxic thiocyanate from methaemoglobin–cyanide
Digoxin Magnesium sulphate i.v. 25–50 mg/kg (0.1–0.2 mmol/kg)
Digoxin Fab i.v: acute − 10 vials per 25 tablets (0.25 mg each), 10 vials per 5 mg elixir; steady state − vials = serum digoxin (ng/mL) × BW (kg)/100		  
Ergotamine Sodium nitroprusside infusion 0.5–5.0 μg/kg/min
Heparin i.v. 100 units/kg then 10 30 units/kg/h		 Treats vasoconstriction. Monitor BP continuously
Monitor partial thromboplastin time
Heparin Protamine 1 mg/100 units heparin  
Iron Desferrioxamine 15 mg/kg/h over 12–24 h if serum iron > 90 or > 63 μmol/L and symptomatic Give slowly; beware anaphylaxis
Lead Dimercaprol (BAL) i.m. 75 mg/m2 4-hourly for 6 doses then i.v. CaNa2 edetate (EDTA) 1500 mg/m2 over 5 days if blood level > 3.38 μmol/L. If asymptomatic and blood level 2.65–3.3 μmol/L, infuse CaNa2 EDTA 1000 mg/m2/day over 5 days or oral succimer 350 mg/m2 8-hourly over 5 days, then 12-hourly over 14 days  
Methaemoglobinaemia Methylene blue i.v. 1–2 mg/kg over several minutes  
Methanol, ethylene glycol, glycol ethers Ethanol i.v. loading dose 10 mL/kg 10% diluted in glucose 5%, then 0.15 mL/kg/h to maintain blood level 0.1% (100 mg/dL)  
Opiates Naloxone i.v. 0.01–0.1 mg/kg, then 0.01 mg/kg/h as needed  
Organophosphates and carbamates Atropine i.v. 20–50 μg/kg every 15 min until secretions dry
Pralidoxime i.v. 25 mg/kg over 15–30 min then 10–20 mg/kg/h for 18 h or more. Not for carbamates		 Blocks muscarinic effects
Reactivates cholinesterase
Paracetamol N-acetylcysteine i.v. 150 mg/kg over 60 min then 10 mg/kg/h for 20–72 h or oral 140 mg/kg, then 17 doses of 70 mg/kg 4-hourly (total 1330 mg/kg over 68 h) Restores glutathione, inhibits metabolites. Give within 18 h according to serum paracetamol level
Phenothiazine dystonia Benztropine i.v or i.m. 0.01–0.03 mg/kg Blocks dopamine reuptake
Potassium Glucose i.v. 0.5 g/kg plus insulin i.v. 0.05 units/kg
Salbutamol aerosol 0.25 mg/kg
Sodium bicarbonate i.v. 1 mmol/kg
Calcium chloride 10% i.v. 0.2 mL/kg
Resonium oral or rectal 0.5–1 g/kg		 Decreases serum potassium rapidly. Monitor serum glucose levels
Decreases serum potassium rapidly
Decreases serum potassium slightly; beware hypocalcaemia
Antagonizes cardiac effects
Adsorbs potassium slowly
Tricyclic antidepressants Sodium bicarbonate i.v. 1 mmol/kg to maintain blood pH > 7.45 Reduces cardiotoxicity

BW, body weight; cAMP, cyclic adenosine monophosphate; EDTA, ethylenediamine tetra-acetic acid.

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Aug 4, 2016 | Posted by in PEDIATRICS | Comments Off on Poisoning and envenomation

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