Poisons Assessment ASSESSMENT Ventilation
Pulse oximetry can be used to measure oxygen saturation. The displayed reading may be inaccurate when the saturation is below 70%, when peripheral perfusion is poor, and in the presence of carboxyhaemoglobin or methaemoglobin.5 Only measurement of arterial blood gases indicates the presence of both hypercapnia and hypoxia. The presence of ventilatory insufficiency (as determined by arterial partial pressure of
oxygen 9 kPa when breathing air and/or arterial partial pres- sure of carbon dioxide 6 kPa) should lead to consideration of intubation and assisted ventilation if the central respiratory
depression cannot be reversed by administration of a specific antidote, such as naloxone.
Circulation
Pulse, blood pressure and temperature (core and peripheral) should be measured to assess cardiovascular function. An ECG should be recorded in moderately or severely poisoned patients, particularly when a drug with a cardiotoxic action (e.g. a tricyclic antidepressant that produces QRS prolongation) has been ingested.
History
Adults About 80% of adults who have ingested an overdose are conscious on arrival at hospital and the diagnosis of self- poisoning can usually be made from the history. In uncon- scious patients, a history from friends or relatives is helpful, and the diagnosis can often be inferred from tablet bottles or a ‘suicide note’ brought by the paramedics, or made by exclusion of other causes. Self-poisoning must always be considered in the differential diagnosis in any patient with an altered level of consciousness. Acutely poisoned patients may be emotionally and psychiat-
rically distressed, and require competent, sympathetic assess- ment if essential information is not to be missed. It is important to try to establish the nature of the substance taken, the amount involved, the route of exposure and the time of exposure, so that the clinical course can be anticipated and the risk assessed. Statements about the nature and amount of what has been
taken should be regarded with clinical suspicion, however, because these are often inconsistent with laboratory analysis of blood or urine.6,7 Patients may not use generic drug names, and it is important to clarify the specific preparation involved because the composition of formulations with similar names can differ. Furthermore, self-poisoning is often an impulsive act involving swallowing the contents of the first bottle or blister pack that comes to hand; sometimes, the drugs used may have been prescribed for another individual. Few patients count the number of tablets taken; the amount is often estimated in unquantifiable terms such as ‘handfuls’ or ‘mouthfuls’, though the patient may be able to recall the number of strips or packets. When the time of exposure is important (e.g. paracetamol poisoning), the accuracy can be improved by relating events to activities of daily life (e.g. the time of a television programme). Assessment of the psychological aspects of self-poisoning is covered on pp 71e73 of this issue.
MEDICINE 40:2 July 2012 49
Children A clear history is unlikely to be obtained from the child, older siblings or a parent. Statements about amounts taken are usually unreliable because the quantities present in containers before such incidents are often unknown.
Circumstantial evidence
Circumstantial evidence is important in establishing a diagnosis of acute poisoning when the patient is very young, has hearing difficulties, or is demented or unconscious. Childrenmaybe foundeatingpotentialpoisons, orwithtablets or
other materials around their mouth or on their clothing. Similar evidence may be found on unconscious adults, or there may be emptydrug containers, tabletsor
capsulesnearby.Alackof personal effects to indicate the identity of anunconscious adult should arouse suspicion of a drug overdose. Protestations of relatives that an individual would never take an overdose are usually incorrect. Suicide notes are reliable indicators of self-poisoning in the absence of evidence of physical violence as a cause of coma.
Examination Physical signs are particularly important when trying to elucidate the cause of unexplained
coma.Adiagnosis of acute poisoning can never be made on the basis of a single physical sign, but there are typical clusters of signs that make a diagnosis of poisoning with specific drugs very likely (Table 2).Head injury should be excluded as a contributing or causative factor in comatose patients. General observations may reveal useful information. For
example, solvents or alcohol may be smelt on the breath, needle track marks may reveal undisclosed illicit substance abuse, atypical bruising may warn of domestic or other violence, and the stigmata of alcoholic liver disease may be apparent.
Skin blisters
Skin blisters may be found in poisoned patients who are, or have been, unconscious.8,9 Such lesions are not diagnostic of specific poisons, but are sufficiently common in poisoned patients (and sufficiently uncommon in patients unconscious from other cau- ses) to be of diagnostic value.
Neurological signs
Lateralizing neurological signs With the exception of transient inequality of pupil size, lateral- izing neurological signs effectively exclude a diagnosis of acute poisoning unless they can be explained by a pre-existing illness.
Pyramidal tract signs The usual features of pyramidal tract involvement (hypertonia, hyper-reflexiaandextensor plantar responses) are commonly found after poisoning with tricyclic antidepressants, and other drugs with marked anticholinergic actions (e.g. the older antihistamines). However, all of these signs may be abolished in deep coma.
Abnormal movements
Decerebrate and decorticate movements of the limbs often occur in unconscious poisoned patients, but in most cases there is no
2011 Published by Elsevier Ltd. Africa Health 41
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