August 11, 2023: How long should an asymptomatic patient be observed following ingestion?


August 11, 2023

First of all, welcome to the Toxicology Question of the Week.  If you are receiving this question, you are on a distribution list if you do not wish to receive it, just send an email and let us know. The Question of the Week was initiated in 2001 and currently has a distribution of more than 3,000 healthcare providers. A toxicology question is proposed and answered in 2-3 paragraphs.  It is less than a 5-minute read and is extremely popular. Please send me any topics you would like addressed. (My apologies for the late start in this academic year-Distribution/IT problems). So here is the first Question of the academic year.

How long should an asymptomatic patient be observed following ingestion?

At first glance, this seems an impossible question to answer. Usually, with some significant exclusions, the answer the Poison Center will give is 6 hours. There is little data, but two recent studies are starting to give us some parameters. Adverse outcomes were determined following a 6-hour observation in asymptomatic patients (ages 13-120 years) with ingestions. 107 patient charts were reviewed. Inclusion criteria required the following to be normal, physical exam, vital signs, basic metabolic panel, ASA, APAP, and EKG. Exclusions included patients with ingestions of xenobiotics, sustained release preparations, antihypertensive agents, Dig, toxic alcohol, lithium, ASA, APAP, sulfonylureas, metformin, and bupropion. 

Four patients required more than 6 hours of observation; one became agitated after a dose of benzo in the ED (paradoxical reaction); another who ingested ibuprofen vomited more than 6 hours after admission; one was admitted for non-toxicology reasons; and one developed tachycardia during the 6-hour observation period after ingestion of amphetamine. The authors concluded that in this cohort of patients, there was a low rate of adverse outcomes during a 6-hour observation.1

A second study evaluated pediatric xenobiotic ingestions in 109 asymptomatic children less than 18 years of age. Exclusions included hydrocarbons, APAP, ASA, sulfonylureas, extended/sustained release agents, and presentation of hypoglycemia. A secondary objective was to explore the impact of vital signs. Five patients in the asymptomatic group with normal vital signs were admitted. Four of the five admissions were determined within 4 hours of presentation. I’ll let you read the details. The authors conclude that in this cohort of patients, observation may require less than 6 hours.2

The theoretical basis for the 6-hour observation period is that the serum concentration of immediate-release agents will peak during that time. I’m not convinced that the peak serum concentration is always reached within that time period-especially with large ingestions that slow gastric emptying or multiple agent ingestions. And we have many drugs now in which clinical symptoms do not correlate with serum concentration-such as drugs that impact receptors. However, determining which patients can safely be discharged without prolonged observation will certainly help the ED run more efficiently. 

Thank goodness the Poison Center is available to recommend observation times for the patients you are evaluating.


1. Keenan M, Rice S, Frawley E et al. Rate of Adverse Outcome During 6-Hour Observation for Asymptomatic Patients with Select Ingestions. Jnl of Medical Toxicology. 2023:19;288-292

2. Capua m, Amlicke M, Esposito E et al.  Time of Observation in Xenobiotic Ingestions in Children. Is 6 hours too long? Pediatr Emerg Care. 2023;39;224-29

Question submitted by Donna Seger.

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