Written by Clay Smith
The HOUR clinical decision rule can help determine which patients with opioid overdose who have received prehospital naloxone are safe for discharge after one hour of observation. But clinician judgment was just as good, which begs the question of why we need a decision rule.
Why does this matter?
Some advocate for a 4-6 hour period of observation after opioid reversal with naloxone, given that the half life of naloxone is shorter than that of some opioids. However, the St. Paul Early Discharge Rule challenged this and showed that a one-hour observation period was safe. But it has not been externally validated. So, there you go.
Another chance for life… and treatment
This was a prospective validation of a modified St. Paul rule for opioid overdose, dubbed Hospital Observation Upon Reversal (HOUR*), which has a higher SpO2 threshold of >95% instead of >92%. Patients were watched for roughly an hour and discharged home after receiving prehospital naloxone if they met all six early discharge criteria. Most naloxone doses, 85%, were given intranasally (IN) at a higher starting dose. IN also has slower onset but higher peak serum concentration than IM or IV, which must be considered when generalizing this information. They enrolled 538 patients. Of these, 82 (15.4%) had an adverse event (AE); one met all discharge criteria yet required more naloxone. The rule was 84% sensitive, 62% specific, and had 96% NPV. Provider judgment had a sensitivity of 85% specificity 61%, NPV 96%, and 2.3% (12/529) had AE based on provider judgment. Most of the study was prospective, but the determination of AE was based on retrospective chart review of the 24h after discharge and medical examiner’s death records for up to 48h post-discharge. This assumes the chart review was thorough and the patient didn’t present to another facility. Based on this, it is reasonable to use this rule, or your best clinical judgment, to risk stratify patients with opioid overdose reversed with naloxone and discharge those with very low risk after a one hour observation period.
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.
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*HOUR Decision Rule
One hour after the administration of naloxone for presumed opioid overdose, patients can be safely discharged from the ED if they meet all six criteria:
Can mobilize as usual
Have a normal O2 saturation (>95%)
Have a normal respiratory rate (>10 and <20 breaths/min)
Have a normal temperature (>35.0 and <37.5°C)
Have a normal heart rate (>50 and <100 beats/min)
Have a GCS score of 15