Abdominal pain assessment in rabbits: using the CANCRS to recognize pain and testing its internal validity over time

A composite scale for pain assessment in rabbits has been previously designed and tested (CANCRS). The present study describes the refinement of the scale and the evaluation of its ability to detect pain variations over time. Furthermore, a comparison between the CANCRS and the Visual Analogue Scale (VAS) has been performed, to underline the differences between an objective (CANCRS) and a subjective (VAS) assessment of abdominal pain. In the first part of the study, 86 rabbits (n=47 heathy patients and n=39 patients with gastrointestinal stasis syndrome) underwent pain assessments with the VAS and the CANCRS. Thirty-two patients with gastrointestinal stasis syndrome participated to the second part of the study. These patients underwent four pain assessments with the CANCRS. The first assessment took place before meloxicam administration and the others after 30, 60 and 90 minutes. The CANCRS showed differences between healthy and diseased rabbits (P = 0.0001), median scores were 5 (IQR 4 - 6) and 9 (IQR 7 - 11) respectively. The VAS showed differences between healthy and diseased rabbits (P = 0.02), the median scores were 4 (IQR 2 - 5.35) and 5.3 (IQR 2.65 - 6.45) respectively. The cut-off scores for the CANCRS and for the VAS for differentiation between healthy and diseased patients were 7 (Sp 89%, Se 79%) and 4.4 (Sp 59%, Se 69%) respectively. Sensitivity and specificity for each parameter of the CANCRS were calculated, in order to obtain weighting factors. Accordingly, the evaluation of respiratory pattern and vocalizations should be excluded from the CANCRS, since their performances in pain evaluation are poor. Internal validity of the CANCRS was tested assessing pain before and after the analgesic treatment and the results showed significancy at each time point. The CANCRS showed better performances than the VAS and its responsiveness to pain variations has been verified.