 Primary Objective: In otherwise healthy children between 3 and 48 months of age who present to a tertiary care emergency department and receive procedural sedation with ketamine, to determine if there is at least a 50 increase, compared to baseline in the serum concentration of any of the neurotoxicity biomarkers S100B, glial fibrillary acidic protein GFAP or neuronal-specific enolase NSE, 1 to 3 hours after intravenous ketamine administration. The cut-off of 50 is a benchmark value routinely quoted in both animal and human studies, which correlated neurotoxicity biomarker levels with functional outcomes. 