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.