Transient amnesia following prehospital low-dose ketamine administration

Low doses of ketamine have been shown to be safe and effective for pain relief. Adverse effects are generally mild and transient. A 69-year-old woman suffered a witnessed ground-level fall without report of head injury, loss of consciousness, or intoxication. She was in severe pain despite 10 mg of intravenous morphine and paramedics provided intravenous ketamine 16 mg (0.19 mg/kg). Upon arrival to the ED, she was alert and oriented. An X-ray demonstrated an acute comminuted nondisplaced right humeral head and neck fracture. Her pain improved after an additional 4 mg of morphine and placement of a sling. Prior to discharge, the patient developed confusion, difficulty finding words, amnesia to the event, and anterograde amnesia evidenced by repetitive questioning. A head CT and a CT angiogram of the patient's head and neck demonstrated no acute abnormalities and an EEG demonstrated no epileptiform activity. The patient was admitted for observation and her mental status gradually improved overnight. She was discharged the following morning. Low dose ketamine is an important therapeutic option. Delayed or prolonged neuropsychiatric effects may be possible following combined ketamine and opioid analgesia. Clinicians utilizing low dose ketamine should be aware of this potential complication as it could result in the need for additional diagnostic testing and prolonged length of stay.