Intravenous Subdissociative-dose Ketamine Versus Morphine for Prehospital Analgesia

Inclusion Criteria:

* older than 18 years old
* prehospital moderate to severe acute pain, defined as a numeric rating scale score greater than or equal to 5

Exclusion Criteria:

* unstable vital signs (systolic blood pressure \<90 or \>200 mm Hg, pulse rate \<50 or \>150 beats/min, and respiration rate \<10 or \>30 breaths/min)
* pregnancy
* breast-feeding
* altered mental status
* unable to give numeric rating scale scores
* allergy to morphine or ketamine
* acute pulmonary edema
* acute coronary syndrome
* renal or hepatic insufficiency
* patient who received morphine for the same acute pain
* acute psychiatric illness