Integration of pain scores, morphine consumption and demand/delivery ratio to evaluate patient-controlled analgesia: the C-SIA score

BACKGROUND Patient-controlled analgesia (PCA) is used to manage postoperative pain. Postoperatively, some patients need to be re-instructed on its correct use. This study explores the efficacy of re-instruction and illustrates a comprehensive version of the Silverman integrated approach (C-SIA), based on the integration of static and dynamic pain scores, morphine consumption, and the ratio between demanded and delivered PCA boluses (the DD ratio). METHODS In total, 50 patients operated on for colorectal surgery were studied retrospectively. The change in DD ratio after re-instruction was analyzed as the primary endpoint. Re-instructed and not re-instructed subjects were compared according to DD ratio, pain scores, and morphine consumption. A secondary comparison was performed using the SIA and C-SIA scores, to illustrate the reliability of the latter tool. Agreement between C-SIA and SIA score was assessed using a Bland-Altman analysis. RESULTS In re-instructed patients, the DD ratio decreased after re-education (P = 0.011). Re-instructed patients had higher DD ratios (P = 0.018) and pain scores at rest (P = 0.024) and movement (P = 0.012) at 24 h after surgery than not re-instructed subjects. These differences disappeared at the 48 h visit. Both the SIA and C-SIA scores reflected these findings. C-SIA scores showed a higher coefficient of correlation with the DD ratio (r = 0.815; P < 0.001) than SIA scores (r = 0.663; P < 0.001). The C-SIA scores, in absolute values, being based on more variables, were, on average, 2.5 times the SIA score. CONCLUSIONS Re-instruction is effective for optimizing PCA therapy. The C-SIA is an alternative to the SIA score that gives an overall measure of PCA therapy efficacy.