Approach to the poisoned patient

Introduction

Drug overdose in adults usually occurs in the context of self-poisoning, which may be either recreational or deliberate.

Deliberate self-poisoning accounts for 1% to 5% of all public hospital admissions in Australia. The bulk of the medical management is carried out in the emergency department (ED), and emergency physicians are expected to be experts. Although management varies considerably depending on the nature and severity of the poisoning, some general principles apply.

Above all, it must be remembered that the acute overdose presentation is only a discrete time-limited event in the course of the underlying condition, which is usually psychosocial in origin.

Pathophysiology and clinical features

The effects of ingestion of pharmaceuticals or illicit drugs range from the non-toxic to the life threatening and may involve any system. Poisoning is a dynamic presentation, and the patient may present at varying points in its time course. Consequently, rapid clinical deterioration or improvement may be observed after the initial presentation and assessment.

Acute morbidity and mortality are usually a consequence of the cardiovascular, respiratory or central nervous system (CNS) complications of the poisoning. Less commonly, hepatic, renal or metabolic effects can be potentially life threatening.

The most frequent life-threatening respiratory manifestation of poisoning is ventilatory failure, which is usually a consequence of CNS depression causing apnoea or bradypnoea. Less commonly, it is secondary to muscle paralysis, direct pulmonary toxicity or non-cardiogenic pulmonary oedema ( Box 25.1.1 ).

Cardiovascular manifestations of poisoning include tachycardia, bradycardia, hypertension, hypotension, conduction defects and arrhythmias ( Box 25.1.2 ). Bradycardia is relatively rare and is associated with a number of potentially life-threatening ingestions, whereas tachycardia is commonly observed and is usually benign. It may be due to intrinsic sympathomimetic or anticholinergic effects of a drug or a reflex response to hypotension or hypoxia. Hypotension is also common and may be due to a number of different mechanisms (see Box 25.1.2 ). Hypertension is usually associated with illicit drug use and is important because it may produce complications such as intracerebral haemorrhage if severe and uncontrolled.