Background: Inpatient subanaesthetic ketamine infusion for 5 days may improve pain and reduce oral opioid usage in patients with chronic pain. Objective: This study aims to investigate pain and psychological outcomes of ketamine parenteral infusion (0.1 -0.35 mg/kg/h or maximum 24 mg/hour) for 5 days in patients with chronic refractory pain. The secondary objective is to explore any prognostic pain and psychological factors associated with the successful response to the ketamine treatment. Methodology: A prospective longitudinal study of a small cohort (N = 35) of patients with heterogenous chronic refractory pain conditions was conducted from one week to two months follow-up. Results: Pain Severity was significantly improved from mean 6.5 to 5.