To describe the safety and efficacy of nitrous oxide during ketamine administration for the prevention of emergence reaction during Emergency Department procedural sedation and analgesia in adults. Drugs such as fentanyl, midazolam, and propofol are widely used in emergency departments for procedural sedation and analgesia because they have a rapid onset and short duration of action. Unfortunately, all of these agents may cause respiratory depression, particularly when combined with other sedative agents, administered in large doses, or given to patients with underlying respiratory diseases. Nitrous oxide use during ketamine administration may be an ideal combination for the prevention of emergence reaction in adults sedated in the ED. Like ketamine, nitrous oxide has an excellent cardio-respiratory profile as well as some analgesic and anxiolytic qualities. The anxiety and pain surrounding procedural sedation is not limited to the procedure itself, but the elapsed time from the time the patient enters the ED to the time spent in preparation for the procedure can be significant and lead to increased anxiety, which may exacerbate emergence reactions in adults. Using nitrous oxide before ketamine administration may mitigate this. While midazolam has shown efficacy in reducing emergence reactions in adults sedated with ketamine, the investigators believe that inhaled nitrous oxide may be equivalent to midazolam, with a better cardio-respiratory profile.