Chapter 34. Poisoning and its treatment
Introduction
The treatment of acute poisoning has of recent years become increasingly important. About 10% of acute medical admissions to hospital are due to an overdose, but 80% of these require only observation until the effects of the poison wear off. Most of the section on general treatment in this chapter applies to the more severely poisoned patient. This may be due to attempted suicide, less often to accidental poisoning and very rarely to homicide. Perhaps the commonest cause of overdosage is an attempt by the patient to draw attention to or modify some intolerable situation. In these circumstances he or she is not seeking death, but merely trying to shock relatives or friends into realization of his or her problems.
In children, poisoning occurs most commonly in the 1–5 year age group as the child becomes mobile and is inclined to put everything in his or her mouth. Drugs and other harmful substances must be kept not only out of reach, but also out of sight, as children are adept at reaching ‘impossible’ places. Occasionally, poisoning may be due to accidental overdose of a drug.
The most frequently used suicide agents are centrally acting drugs such as sedatives, hypnotics and antidepressants, analgesics such as aspirin, paracetamol and opioids, and a mixed bag which includes cardiovascular drugs. Coal gas, although still used, is less common than formerly, as methane has replaced it for domestic use. In addition, poisoning can occur, particularly in children, from various chemicals used domestically or in the garden and from a number of berries.
General management
When a patient is admitted to hospital suffering from poisoning the first step is to decide if life is at immediate risk from airway obstruction or respiratory arrest. If so, the appropriate measures should be taken at once.
The next steps are to assess the severity of the poisoning, the nature of the poison used (overdose by more than one drug is common) and to institute appropriate treatment.
Severity of poisoning
The severity of the poisoning will be assessed largely on three criteria:
• level of consciousness
• circulation
• respiration.
Level of consciousness
This is usually classified into four grades:
• Grade I: drowsy, but responds to light stimulation
• Grade II: unconscious, but responds to light stimulation
• Grade III: unconscious, but responds to severe stimulation
• Grade IV: unconscious, with no response to stimulation.
Circulation
Many drugs cause circulatory failure. The nurse is frequently asked to measure the blood pressure at intervals and a low blood pressure is indicative of failing circulation. However, it must be realized that what really matters is the perfusion of vital organs such as the brain and kidney. It is possible to have a reasonable blood pressure maintained by intense constriction of blood vessels, but organ perfusion will be poor. In such a situation the hands and feet will be cold and blue and this may be a useful sign. In addition, certain drugs (particularly antidepressants) can cause cardiac arrhythmias, so ECG monitoring is necessary.
Respiration
Depression of respiration so that less oxygen reaches the lungs is a common cause of death in overdosage. Respiratory rate should be charted at regular intervals. Cyanosis is a useful sign of under-ventilation of the lungs, and the respiratory minute volume and blood gases must be measured.
Nature of poison used
The identification of the poison used will depend on history and circumstantial evidence, on clinical signs and on analysis of gastric aspirate, blood and urine. Samples should be collected, carefully labelled and analysed as soon as possible. The results not only may be useful in the management of the patient but also may have medicolegal implications.
Treatment
The treatment of poisoning can be divided into:
• non-specific measures
• specific measures, which are considered under individual poisons.
Non-specific measures
Non-specific measures comprise procedures A–F, which are described below.
A. Maintenance of ventilation
In the unconscious patient the reflexes which protect the airways may be lost, so there is a danger of respiratory obstruction by the tongue and the aspiration of vomit. These patients should be nursed in the coma position with an airway in place until it is possible to insert a cuffed endotracheal tube, which can be kept in place for up to 72 hours. Secretions should be aspirated regularly.
With severe respiratory depression, oxygen and/or assisted ventilation will be required.
B. Reducing absorption of poisons
It is obviously desirable to minimize the absorption of poison from the gut and this can be achieved in two ways:
• emptying the stomach by emesis or washouts
• giving substances which bind to the poison in the gut and thus prevent its absorption.
Emptying the stomach
If the patient is conscious, vomiting can be induced by stimulation of the posterior pharyngeal wall.
Lavage
In the unconscious patient, lavage may be used:
• When dangerous amounts of poison have been taken within the previous hour; a longer period is reasonable with certain drugs, e.g.
salicylates 4 hours
tricyclic antidepressants 4 hours
opioids 4 hours
• After a cuffed endotracheal tube has been inserted, as there is considerable risk of inhalation of vomit in these patients.
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