Morphine or Ketamine for Analgesia

Aim 1: To determine if IV sub-dissociative ketamine is non-inferior to IV morphine for decreasing pain intensity in children presenting to an ED with acute pain. The investigators hypothesize that IV sub-dissociative ketamine is non-inferior to IV morphine for decreasing pain intensity in children with acute abdominal pain or an extremity fracture. Aim 2: To compare the rate of acute (\<2 hours) adverse events, including cardiopulmonary adverse events, associated with IV sub-dissociative ketamine and IV morphine. The investigators hypothesize that there is a smaller proportion of cardiopulmonary adverse events associated with IV sub-dissociative ketamine compared to IV morphine. Aim 3: To determine the relationship between ketamine and long-term sequelae of acute pain. The investigators hypothesize that children who receive ketamine will have better levels of pain-related function during the first week following ED presentation and will have greater odds of experiencing more favorable post-traumatic stress, anxiety and depression outcomes 1-6 months after ED presentation compared to children who received IV morphine.