Emergency department observation of poisoned patients: how long is necessary?

OBJECTIVE: To compare the emergency physician disposition decisions after observation periods of two, four, and six hours in a single cohort of ED patients with acute intentional ingestion to determine the accuracy of disposition decisions at two and four hours relative to the six-hour period of observation.
METHODS: This was a prospective observational study at two university hospital EDs. Study participants were patients with potentially toxic oral ingestions occurring less than six hours prior to ED presentation. Patients with isolated recreational drug or ethanol use were excluded. Structured data forms were completed at presentation, and two, four, and six hours later. Data included signs and symptoms consistent with toxic ingestion, physical examination, laboratory determinations, medications ingested, treatment, and suicide risk. At two and four hours, physicians were asked to determine whether they thought the patient was safe for medical clearance. These patients continued to be observed for six hours. The main outcome was whether patients initially thought to be appropriate for early medical clearance were ultimately cleared at six hours.
RESULTS: There were 260 patients enrolled: 28 were immediately admitted to the hospital and 17 were immediately discharged; 215 entered ED observation. Patients had a mean age of 24 years; 55% were female; 50% were suicidal; 17% had toxidromes. Of the 215 observed patients, 106 (49%) were deemed safe for early medical clearance at two hours. All 106 were ultimately cleared at six hours (100%, 95% CI = 97% to 100%). Of the 109 not safe for early medical clearance at two hours, 61 (56%) were deemed safe for early medical clearance at four hours; all 61 were subsequently discharged at six hours (100%; 95% CI = 95% to 100%). Overall, 167 of 215 (77%) observed overdose patients were deemed safe for early medical clearance after two or four hours of observation. All 167 were ultimately cleared at six hours (100%; 95% CI = 98.2% to 100%).
CONCLUSIONS: A large subset of overdose patients who are medically cleared after six hours of observation can be identified within two to four hours of presentation. No patient who was believed to be safe for medical clearance at either two or four hours had a complication within the six-hour time period (95% CI = 0% to 1.8%). These data suggest that asymptomatic patients with selected acute intentional ingestions can be released from medical observation in less than six hours.