Effects of low-dose IV ketamine on peripheral and central pain from major limb injuries sustained in combat.

Objective: Examine response patterns to low-dose intravenous (IV) ketamine continuous infusions on multiple pain outcomes, and demonstrate effectiveness, safety, and tolerability of ketamine administration on general wards.

Design: Retrospective case series of consecutive patients given low-dose IV ketamine continuous infusions.

Setting: Walter Reed Army Medical Center, Washington, DC.

Patients: Nineteen eligible inpatients with neuropathic pain from major limb injuries sustained in combat with inadequate pain control from multimodal analgesia.

Interventions: A 3-day IV infusion of ketamine at doses ≤ 120 μg/kg/h.

Outcome Measures: Daily present (PPI), average (API), and worst (WPI) pain intensity (0-10), global pain relief (GPR) (1 "no relief" to 5 "complete relief"), daily assessments of adverse events, and daily opioid requirements measured during therapy.

Results: A significant reduction in PPI (P < 0.001) and improvement in GPR (P = 0.031) was noted over time. Higher baseline WPI (≥ 7; N = 4) was associated with a significant decrease in WPI (P = 0.0388), but lower baseline WPI (N = 5) was not. Significant mean percent decreases in PPI with higher baseline PPI (N = 8; P = 0.0078) and WPI with no phantom limb pain (PLP) (N = 10; P = 0.0436) were observed. Mean percent increase in overall GPR was better for those reporting GPR scores ≤ 3 (N = 13) in the first 24 hours of therapy (P = 0.0153). While not significant, mean opioid requirement (IV morphine equivalents) decreased from 129.9 mgs ± 137.3 on day 1 to 112.14 ± 86.3 24 hours after therapy.

Conclusions: Low-dose ketamine infusions for complex combat injury pain were safe and effective, and demonstrated response patterns over time and by baseline pain score stratification and presence or absence of PLP.