Objective pain scales in horses with facial pain
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Animal pain is an aversive sensory and emotional experience representing awareness by the animal of damage or threat to the integrity of its tissues; it changes the animal’s physiology and behavior to reduce or avoid damage, to reduce the likelihood of recurrence and to promote recovery. To provide every animal with individual tailored pain management, the recognition of pain is very important. Furthermore, the assessment of pain in animals is also very important for clinical evaluation and decision making. Unfortunately pain in animals is very difficult and hard to measure, unlike in verbal humans. The aim of this study was the construction and internal validation of objective pain scales and comparison of different pain scales in horses with facial pain. Eight horses of various breeds (3-19 years old) with different painful conditions of the head admitted to the Equine Health Department of the Faculty of Veterinary Medicine in Utrecht between 19/08/2013 and 6/10/2013 were used for this study. Painful conditions included for example uveitis, sinusitis, jaw fractures and post-surgical trauma. The control group consisted of eight horses owned by the Department of Equine Sciences, seven mares and one gelding (4-15 years old, various breeds) which in daily life are used for education. Three pain scales were used to score the amount of pain: the Composite Pain Scale (CPS), the Facial Expression Pain Scale (FEPS) and the existing Visual Analogue Scale (VAS). Scoring of CPS and FEPS were performed independently at the same time by two observers, not blinded for the reason of admittance or treatment of the case. The VAS score was given by the treating vet at the Equine Clinic. Scoring of the CPS and FEPS was performed at several moments during the days following admittance to monitor the pain and notice the changes in pain in time. Horses that did not undergo surgery where scored at T=0, T=1st morning and T=2nd morning. The cases which underwent surgery were scored at T=0 pre- surgery, T=0 post-surgery, T= 1st morning, T=1st afternoon, T=2nd morning and T=2nd afternoon post-surgery. During pain scoring all horses (cases and controls) were placed in the same standard stable. The FEPS was also scored during one minute in the stable where the cases resided during hospitalization (own stable: FEPSos). The correlation coefficient between the two observers was highly significant (p<0.01) for the CPS (r=0.921**), FEPS (r=0.823**) and FEPSos (r=0.911**). Distribution of FEPSos was not the same between the subgroups and a significant difference in the pain scores of controls and cases existed, which was not seen in the FEPS and CPS score. The FEPSos showed a very high sensitivity (99.99%) and specificity (99.99%) for facial pain. There is no significant correlation between the VAS score (golden standard) and the tested pain scales. In the timelines of all scoring systems (CPS, FEPS, FEPSos) most cases show an increase in pain score at 4/5 hours or 24 hours post-surgery, the pain score gradually drops after 36 hours post-surgery, with exception of some cases. The conclusion of this study is that a FEPS score in the horse’ own stable is the most reliable and useful pain scoring system to assess pain in horses with facial pain.