Psychiatric Outcomes of Patients With Severe Agitation Following Administration of Prehospital Ketamine

Ketamine is an emerging drug used in the management of undifferentiated, severe agitation in the prehospital setting. However, prior work has indicated that ketamine may exacerbate psychotic symptoms in patients with schizophrenia. The objective of this study was to describe psychiatric outcomes in patients who receive prehospital ketamine for severe agitation.

This is a retrospective cohort study, conducted at two tertiary academic medical centers, utilizing chart review of patients requiring prehospital sedation for severe agitation from January 1, 2014, to June 30, 2016. Patients received either intramuscular (IM) versus intravenous (IV) ketamine or IM versus IV benzodiazepine. The primary outcome was psychiatric inpatient admission with secondary outcomes including ED psychiatric evaluation and nonpsychiatric inpatient admission. Generalized estimating equations and Fisher's exact tests were used to compare cohorts.

During the study period, 141 patient encounters met inclusion with 59 (42%) receiving prehospital ketamine. There were no statistically significant differences between the ketamine and benzodiazepine cohorts for psychiatric inpatient admission (6.8% vs. 2.4%, difference = 4.3%, 95% CI = -2% to 12%, p = 0.23) or ED psychiatric evaluation (8.6% vs. 15%, difference = -6.8%, 95% CI = -18% to 5%, p = 0.23). Patients with schizophrenia who received ketamine did not require psychiatric inpatient admission (17% vs. 10%, difference = 6.7%, 95% CI = -46% to 79%, p = 0.63) or ED psychiatric evaluation (17% vs. 50%, difference = -33%, 95% CI = -100% to 33%, p = 0.55) significantly more than those who received benzodiazepines, although the subgroup was small (n = 16). While there was no significant difference in the nonpsychiatric admission rate between the ketamine and benzodiazepine cohorts (35% vs. 51%, p = 0.082), nonpsychiatric admissions in the benzodiazepine cohort were largely driven by intubation (63% vs. 3.8%, difference = 59%, 95% CI = 38% to 79%, p < 0.001).

Administration of prehospital ketamine for severe agitation was not associated with an increase in the rate of psychiatric evaluation in the emergency department or psychiatric inpatient admission when compared with benzodiazepine treatment, regardless of the patient's psychiatric history.