Acute poisoning and overdoses - MEDICAL EDUCATION at ...

10
Management of Acute Poisoning and Overdose
E Powell
Acute poisoning is a common emergency that presents to the accident and emergency
(A & E) department and to intensive care. Patients may be unconscious at the time of
presentation and appropriate history may not be available. Poisoning may be
accidental, iatrogenic or may be due to suicidal intention. The majority of the patients
are young, otherwise medically fit and they will recover with basic supportive care.
These patients are initially assessed and managed in A&E. They may require
admission to intensive care for following reasons
• Altered level of consciousness
• Respiratory failure
• Cardiac arrhythmias
• Cardiac conduction disturbances resulting A-V block
• Hypotension
• Acute renal failure
Drug overdose may occur through several routes: oral, inhaled, skin contact or
intravenous. The following are the most commonly consumed poisons.
• Industrial or agricultural chemicals
• Household products
• Plant and animal toxins, fumes
• Recreational drugs: Amphetamines, Ecstasy
Following are the most commonly consumed drugs.
• Paracetamol
• Tricyclic antidepressants (dothiepin, amitriptyline)
• Salicylates (aspirin)
• Opioids (codeine, morphine, diamorphine)
• Amphetamines, cocaine, ecstasy
• Benzodiazepines (diazepam, temazepam)
General principles of management
Drug overdose should always be considered in an unconscious patient. Assessment
and resuscitation should go side by side. General principle of management involves
assessment, resuscitation and diagnosis of specific poison. In circumstances where
patient is unable to provide history, contacting relatives or general practitioner may
provide useful information.
• Resuscitation using ABC (airway, breathing and circulation) approach.
• Identification of type of overdose, type of drug and amount
• Limiting the absorption of drug
• Enhancing the elimination of drug
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• Specific treatments and antidotes
• Continued supportive care of A,B,C
• Psychiatric review if deliberate overdose
Resuscitation: ABC
The airway should be assessed and managed using basic airway manoeuvres and
simple adjuncts. High flow (10-15 l/min) of oxygen should be administered using
facemask with reservoir bag. The respiratory rate and tidal volume should be assessed
to rule out hypoventilation. For the following situations definitive airway management
using orotracheal intubation may be required.
• Loss of airway due to reduced conscious level (GCS < 9/15, responsive to pain
only on AVPU scale: A [alert] V [response to Verbal commands] P [response
to Pain] U [Unresponsive].
• Unprotected airway due to reduced conscious level (GCS < 9/15, AVPU-Pain)
• Loss of airway due to seizures
• Airway oedema due to smoke inhalation (CO poisoning)
Breathing problems
• Reduced respiratory rate or volume (sedative drugs, depressed conscious level)
• Increased respiratory rate or volume (salicylate poisoning)
• Aspiration of gastric contents (depressed conscious level)
• Direct lung damage due to certain agents (irritant gases)
All of the above problems require senior help and may require admission to ICU.
Circulatory problems
• Hypotension- myocardial depression, peripheral vasodilation.
• Hypertension (amphetamines).
• Arrhythmias-bradycardias, tachycardias, abnormal rhythms, irregular rhythms
(tricyclics, beta blockers, digoxin, lithium).
Management of circulatory problems includes intravenous access and fluid
resuscitation. Hypotension and low cardiac output may require invasive monitoring
and inotropic support. Hypertension should be controlled using anti-hypertensives
(glyceryl trinitrate infusion).
Identification of type of overdose (type and amount of drug)
This will involve accurate history from the patient, relatives and paramedics. Often
cocktail of drugs and alcohol are consumed by the patient. The patient’s usual
medications, previous history and previous hospital admissions are likely to reveal the
possible drugs that might have been consumed by the patient.
Clinical examination
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• Drowsiness or sedation- alcohol, opioids, benzodiazepines, tricyclic
antidepressants (TCAs)
• Pupil: mydriasis- TCA’s, cocaine, ecstasy; miosis- opioids, organophosphates
• Tachypnoea- salicylates, carbon monoxide
• Hypoventilation- sedative drugs
• Bradycardia- digoxin, beta blockers
• Tachycardia- cocaine, TCAs
• Wide QRS and dysrrythmias- TCA’s
• Seizures- TCAs, theophylline
• Cherry red skin- carbon monoxide poisoning
• Hypothermia- sedative drugs
• Hyperthermia- salicylates, amphetamines, cocaine, ecstasy
Investigations
• Plasma and urine toxicology
• Blood tests to identify electrolyte abnormalities, derangement of acid/ base
balance and organ damage.
• ECG to detect changes in PR interval, QRS length, rhythm, rate
• Chest X ray: only useful when pulmonary oedema or aspiration is suspected.
Specific advice regarding management can be obtained from regional poisons centre
via internet or telephone
Limiting the absorption of drug
• Gastric lavage- inserting NG tube and aspirating gastric contents.
-lavage with tepid water.
-only useful if done within one hour of ingestion.
-airway should be protected if conscious level decreased.
• Emesis- no longer routine practice
• Activated charcoal -binds to the drug in the stomach so it is not absorbed
-only effective in first hour after ingestion
-can be given in repeated doses to increase elimination of
some drugs from the blood (e.g. digoxin)
Enhancing the elimination of drug
• Forced diuresis- infusing fluids to increase urine output and therefore
increasing elimination of the drug.
• pH manipulation-altering pH of urine to increase elimination of the drug.
Alkalisation of urine enhances the excretion of acidic drugs such as salicylates
and phenobarbitone. Acidification of urine enhances the excretion of alkaline
drugs such as amphetamines.
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• Haemodialysis is useful for drugs with low protein binding and small volume
of distribution.
Specific treatments and antidotes
Paracetamol (Acetaminophen)
• Often no symptoms or signs.
• 150mg/kg can be fatal.
• Causes hepatocellular necrosis in overdose due to saturation of metabolic
pathways and exhaustion of glutathione stores.
• Replenish glutathione with methionine (oral) or N-acetyl cysteine (iv).
• Treat according to nomogram. N-acetyl cysteine should be given if serum
paracetamol level is more than 200mg /L at 4 hrs, 100mg/L at 8 hrs or 50mg/L
at 12 hrs of ingestion.
• Liver function, creatinine, INR and blood gas analysis should be performed if
the presentation is delayed.
• Patient should be transferred to specialist unit if there are signs of cerebral
encephalopathy, INR >2.0, presence of acidosis and renal impairment.
Sedative drugs
• Patients who have taken opioids or benzodiazepines (BZD) in overdose are
likely to present with a depression of cardio-respiratory function and a reduced
level of consciousness
• Initial aims are to support ABC
• Specific antidotes can be used (naloxone for opioids, flumazenil for BZD)
Carbon Monoxide (CO)
• Patients with CO poisoning may have other injuries (e.g. burns).
• Symptoms and signs relate to hypoxaemia.
• Cherry red colour of mucous membranes.
• Carbon monoxide has a much higher affinity for haemoglobin than oxygen.
Hence it reduces the oxygen delivery to body tissues.
• Treatment is ABC followed by high flow oxygen, reduces the half life of
carboxyhaemoglobin.
• Hyperbaric oxygen is sometimes used. This increases the dissolved oxygen in
blood so that oxygen delivery is less dependent on Hb and also reduces the
half life of carboxyhaemoglobin.
Tricyclic antidepressants (TCAs)
• These drugs have anti-cholinergic effects-dry mouth, dry skin, dilated pupils
and tachycardia.
• They produce a metabolic acidosis, wide QRS complex, prolonged PR interval
arrhythmias, convulsions and coma.
• Treatment of ABC
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• Activated charcoal (if patient presents within 3-4 hrs)
• Correction of acid base disturbance is fundamental.
• Treatment of seizures with lorazepam/diazepam.
• Often need supportive care on ICU.
Salicylates
• Aspirin is a weak acid
• It uncouples oxidative phosphorylation (therefore anaerobic metabolism
predominates resulting in lactic acidosis)
• Vomiting, dizziness, tinnitus, hyperventilation (early)
• It produces mixed respiratory alkalosis and metabolic acidosis.
• Seizures, hypotension, heart block, coma (late)
• Supportive management
• Correct acid/base disturbance
• Consider alkalinisation of urine to increase elimination.
• In severe poisoning, haemodialysis should be considered.
Continued Supportive care of ABC
This involves supporting the cardio-respiratory system until the patient has recovered
from the adverse physiological effects of the overdose. It can mean a period of
ventilation and inotropic support on intensive care.
Psychiatric review
For patients with possible intentional overdose a psychiatric review should be
requested. This should take place before the patient is discharged from hospital.
Further reading
T.E. Oh. Intensive Care Manual, 4 th Edn. London: Butterworth-Heinemann, 1997.
Appleboam R. Emergency management of poisoning. Anaesthesia update; 2004,
(issue 18). http:// www.nda.ox.ac.uk
RA Hope, JM Longmore, TJ Hodgetts and PS Rarakha. Oxford handbook of
medicine. 3 rd Edn. Oxford University Press, 1993.
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