Responders and non-responders to post-operative pain treatment: the loading dose predicts analgesic needs

The study compares responders and non-responders to post-operative patient- controlled analgesia (PCA) and evaluates factors that might differ between these two groups in order to identify non-responders during the early post- operative period. A prospective, randomized, double-blinded study design wa s used. Patients recovering from abdominal surgery were assigned to one of three treatment groups for a study period of 48 h. After titration of an in dividual loading dose, patients could self-administer 1 mL bolus doses (2 m g of morphine, 20 mg of tramadol or placebo) using a PCA device. Patients r esponding or not responding to the treatment were identified. In non-respon ders the escape medication was morphine. There were 96 responders and 65 no n-responders. All responders showed similar pain scores, irrespective of th e drug they received. Drug consumption of placebo responders was twice as h igh as that of opioid responders. Pain scores and analgesic consumption of non-responders were significantly higher compared with responders, although those patients received morphine. The loading dose correlated with subsequ ent analgesic consumption. Altogether, 89.2% of the non-responders were ide ntified after the loading dose. Size of loading dose and pain scores during the first 30 min are useful for assessing the overall response to post-ope rative pain management. These factors may be valuable for predicting indivi dual pain management.