Hospital Observation Upon Reversal (HOUR) With Naloxone: A Prospective Clinical Prediction Rule Validation Study

Acad Emerg Med. 2019 Jan;26(1):7-15. doi: 10.1111/acem.13567. Epub 2018 Dec 28.


Objective: St. Paul's Early Discharge Rule was derived to determine which patients could be safely discharged from the emergency department after a 1-hour observation period following naloxone administration for opiate overdose. The rule suggested that patients could be safely discharged if they could mobilize as usual and had a normal oxygen saturation, respiratory rate, temperature, heart rate, and Glasgow Coma Scale score. Validation of the St. Paul's Early Discharge Rule is necessary to ensure that these criteria are appropriate to apply to patients presenting after an unintentional presumed opioid overdose in the context of emerging synthetic opioids and expanded naloxone access.

Methods: In this prospective, observational validation study, emergency medicine providers assessed patients 1 hour after administration of prehospital naloxone. Unlike in the derivation study the threshold for normal oxygen saturation was set at 95% and patients were not immediately discharged after a normal 1-hour evaluation. Patients were judged to have a normal 1-hour evaluation if all six criteria of the rule were met. Patients were judged to have an adverse event (AE) if they had one or more of the preestablished AEs.

Results: A total of 538 patients received at least one administration of prehospital naloxone, were transported to the study hospital, and had a 1-hour evaluation performed by a provider. AEs occurred in 82 (15.4%) patients. The rule exhibited a sensitivity of 84.1% (95% confidence interval [CI] = 76.2%-92.1%), a specificity of 62.1% (95% CI = 57.6%-66.5%), and a negative predictive value of 95.6% (95% CI = 93.3%-97.9%). Only one patient with a normal 1-hour evaluation subsequently received additional naloxone following a presumed heroin overdose.

Conclusion: This rule may be used to risk stratify patients for early discharge following naloxone administration for suspected opioid overdose.

Publication types

  • Observational Study
  • Validation Study

MeSH terms

  • Adult
  • Analgesics, Opioid / poisoning*
  • Decision Support Techniques*
  • Drug Overdose / drug therapy
  • Emergency Service, Hospital
  • Female
  • Humans
  • Male
  • Middle Aged
  • Naloxone / therapeutic use*
  • Narcotic Antagonists / therapeutic use*
  • Patient Discharge*
  • Predictive Value of Tests
  • Prospective Studies


  • Analgesics, Opioid
  • Narcotic Antagonists
  • Naloxone