Abstract & Commentary
Source: Hartington K, et al. Measuring plasma paracetamol concentrations in all patients with drug overdoses: Development of a clinical decision rule and clinicians willingness to use it. Emerg Med J 2002;19:408-411.
Paracetamol (acetaminophen) overdose is a common type of ingestion seen in emergency departments (EDs). Most emergency physicians routinely screen all suspected intentional overdose patients for paracetamol ingestion due to the nonspecific or non-existent signs and symptoms of early paracetamol overdose. However, this practice leads to a large number of negative paracetamol screening tests.
The authors of this study proposed and tested the following clinical decision rule: Patients presenting to the ED after a deliberate overdose do not need paracetamol level testing if they: a) deny paracetamol ingestion; b) present with a Glasgow Coma Scale score (GCS) of 15; c) understand English; and d) have not consumed an excessive amount of alcohol.
In a British ED, 307 consecutive patients older than 16 years of age were screened using the decision rule, and had plasma paracetamol concentrations determined at presentation or at four hours post-ingestion, whichever was later. Of the 307 patients in the study group, 152 admitted to ingesting paracetamol or paracetamol-containing preparations. Of the 155 patients who denied paracetamol ingestion, 13 (8%) had detectable plasma paracetamol levels. None of these patients required n-acetylcysteine.
Among the 13 patients with a negative history for paracetamol and a measurable paracetamol level, three (23%) would not have been identified using the proposed clinical decision rule. If the decision rule had been applied to the group with a negative history of paracetamol ingestion (n = 155), only 46 had a GCS of 15 and no significant alcohol co-ingestion. Thus, only 15% (46 of 307) of the patients presenting with intentional overdose would have been spared a plasma paracetamol level determination.
The authors also surveyed 47 emergency physicians in five EDs to determine the level of confidence that clinicians would require to implement a decision rule to avoid routine paracetamol level determinations. Eighty-three percent of these clinicians reported that they would require a false-negative rate of 0.1%.
The authors conclude that they cannot, based upon this study, recommend changing the widespread practice of routinely checking all overdoses for paracetamol, even if the patient denies paracetamol ingestion.
Commentary by Jacob W. Ufberg, MD
This study reinforces the belief among emergency physicians that overdose patients are unreliable historians, either because they intentionally lie, or because they ingest certain medications without knowledge of the ingredients. Not only did the proposed clinical decision rule miss patients who ingested paracetamol, but it also eliminated only a small percentage of orders for plasma paracetamol levels.
Based on the available evidence, the care of the patient with an intentional overdose does not appear to be the place for cutting corners. Tests to determine paracetamol levels are relatively inexpensive, lab turnaround times are fast, the antidote is effective, and the consequences of missing a significant overdose are disastrous. Moreover, the optimal time period for treatment with antidote coincides with a relatively symptom-free time window after ingestion, making the screening test a valuable tool in the management of possible paracetamol toxicity.
Dr. Ufberg, Assistant Professor of Emergency Medicine, Assistant Residency Director, Department of Emergency Medicine, Temple University School of Medicine, Philadelphia, PA, is on the Editorial Board of Emergency Medicine Alert.
The authors of this study proposed and tested the following clinical decision rule: Patients presenting to the ED after a deliberate overdose do not need paracetamol level testing if they: a) deny paracetamol ingestion; b) present with a Glasgow Coma Scale score of 15; c) understand English; and d) have not consumed an excessive amount of alcohol.
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