Evaluation of the parasympathetic tone activity (PTA) for posttraumatic pain assessment in awake dogs before orthopaedic surgery - A prospective non-randomised clinical study.

Study Design: A prospective non-randomised clinical study.

Animals: A study group with 18 posttraumatic dogs before surgery and a control group with nine healthy dogs.

Methods: Two different examiners evaluated the pain using two multidimensional pain scales (the Canine Acute Pain Scale of the Colorado State University (CSU-CAPS) and the Modified Glasgow Pain Scale (MGPS)) before the administration of methadone. During the administration of methadone, the Parasympathetic Tone Activity (PTA) was measured. In the control group, the PTA was measured without administration of methadone. In the statistical evaluation, correlation between PTA value and pain scores, and the predictive value of the PTA value in determining whether the animal was classified as painful was investigated. In addition, the results of the different pain scales and the results of the different examiners were compared.

Results: The average PTA values of the control group were 45.67 (± 13.64). Two of nine (22.22%) animals in the control group have their average PTA value above the 'pain-free state' of 50. The average PTA values of the study group were 56.16 (± 15.11) and 51.05 (± 13.24) before and after methadone administration, respectively. Comparing the average values of the study group 30 s before methadone administration with the average values of the control group, there was no significant difference (p = 0.5403). Examiner A (experienced) classified 14 of 16 animals (87.5%) with the CSU-CAPS, and examiner A2 (inexperienced) classified 7 of 16 patients (43.75%) as painful. In 56.25% of the cases, both examiners (A and A2) reached the same decision when using CSU-CAPS. When using the MGPS, 10 of 18 patients (55.56%) reached the intervention level regardless of the examiner. In 88.89% of the cases, the two examiners reached the same decision; there is a highly positive correlation between the two examiners (Spearman correlation coefficient rs = 0.84). There was no correlation between the monitor and score values of both pain scales with either examiner.

Conclusion: The PTA monitor on the awake animal was not suitable for pain detection. There were no statistically significant correlations of PTA scores with pain scale scores, regardless of the examiner. Similarly, the tendency for the study group to have lower PTA scores indicates that PTA also appears to be influenced by environmental factors.