BACKGROUND: There are no published reports examining the effects that ketamine administered prior to hospital arrival has on patients after their transfer to the emergency department (ED). OBJECTIVE: In order to better understand the risk-benefit ratio for the prehospital use of ketamine, we examined the ED courses of 13 patients to whom emergency medical services (EMS) had administered ketamine for chemical restraint. METHODS: This project was undertaken as part of our EMS system's continuous quality improvement (CQI) process. Data were collected retrospectively. All patients who were given ketamine by EMS providers under our medical direction were identified by prehospital care report queries. The treating paramedic and emergency physician were provided a CQI form after disposition of the patient from their care. The data were tabulated and descriptive statistics were calculated. RESULTS: Thirteen patients were given ketamine by EMS providers, with 13 of 13 having EMS records and 12 of 13 having ED records available for review. Time from ketamine administration to peak sedation was <5 minutes in 11 patients and 20 minutes for two patients. On emergency physician examination, five of 12 patients had Richmond Agitation Sedation Scale (RASS) scores of -5 (unarousable), one of 12 had a RASS score of -4 (deep sedation), four of 12 had RASS scores of -3 (moderate sedation), and two of 12 had RASS scores of -2 (light sedation). Three patients developed hypoxia, two in the ED and one prior to hospital arrival. Two of these patients required intubation and one was treated with jaw thrust. Indications for intubation were recurrent laryngospasm and intracranial bleeding. One additional patient experienced a single episode of hypersalivation, which was successfully treated with suctioning of the oropharynx. Of the nonintubated patients, three of 10 were diagnosed with an emergence reaction and five of 10 required additional sedation. The primary diagnosis on ED disposition was drug/ethanol intoxication (3), psychosis (4), intracranial bleeding (1), seizure (1), suicidal ideation (1), agitation (1), and altered mental status (1). Five patients were discharged from the ED, seven were admitted (two to the intensive care unit, four to medicine, and one to psychiatry), and one patient's disposition was unknown. CONCLUSIONS: In this series of 13 patients, ketamine administered by EMS produced moderate or deeper sedation. Respiratory complications included hypoxia, laryngospasm, and hypersalivation. Emergence reactions occurred in 30% of nonintubated patients, but they were successfully treated with small doses of benzodiazepines.