Fig. 1. Mean visual analog scale (VAS) pain scores over 24 h for preemptive versus postincisional treatment. Each point represents an individual trial. 9(A ) Nonsteroidal antiinflammatory drugs (NSAIDs)–paracetamol. Results from the 19 trials where pain scores were available (all except reference 37). (B ) Intravenous opioids. Results from the nine treatment arms. (C ) N -methyl-d-aspartate (NMDA) receptor antagonists. Each square represents an individual study of ketamine, and each triangle represents an individual study of dextromethorphan.