Clinical Use of The Parasympathetic Tone Activity Index As a Measurement of Postoperative Analgaesia in Dogs Undergoing Ovariohysterectomy

INTRODUCTION: While the current tools to assess canine postoperative pain using physiological and behavioural parameters are reliable, an objective method such as the parasympathetic tone activity (PTA) index could improve postoperative care. The aim of the study was to determine the utility of the PTA index in assessing postoperative analgaesia. MATERIAL AND METHODS: Thirty healthy bitches of different breeds were randomly allocated into three groups for analgaesic treatment: the paracetamol group (G(PARAC), n = 10) received 15 mg/kg b.w., the carprofen group (G(CARP), n = 10) 4 mg/kg b.w., and the meloxicam group (G(MELOX), n = 10) 0.2 mg/kg b.w. for 48 h after surgery. G(PARAC) was medicated orally every 8 h, while G(CARP) and G(MELOX) were medicated intravenously every 24 h. The PTA index was used to measure the analgaesia–nociception balance 1 h before surgery (baseline), and at 1, 2, 4, 6, 8, 12, 16, 20, 24, 36, and 48 h after, at which times evaluation on the University of Melbourne Pain Scale (UMPS) was made. RESULTS: The baseline PTA index was 65 ± 8 for G(PARAC), 65 ± 7 for G(CARP), and 62 ± 5 for G(MELOX). Postoperatively, it was 65 ± 9 for G(PARAC), 63 ± 8 for G(CARP), and 65 ± 8 for G(MELOX). No statistically significant difference existed between baseline values or between values directly after treatments (P = 0.99 and P = 0.97, respectively). The PTA index showed a sensitivity of 40%, specificity of 98.46% and a negative predictive value of 99.07%. CONCLUSION: Our findings suggest that the PTA index measures comfort and postoperative analgaesia objectively, since it showed a clinical relationship with the UMPS.