Preliminary Investigations of Pain and Analgesia Assessment in Horses Administered Phenylbutazone or Placebo After Arthroscopic Surgery

Abstract

Twenty-five horses undergoing arthroscopic surgery were studied to develop a scheme for assessing pain in horses while investigating the effects of phenylbutazone (PBZ) analgesia. Fifteen of the 25 horses received PBZ 4 mg/kg intravenously (IV) before surgery and 2 mg/kg (IV) every 12 hours thereafter until 60 hours; the remaining 10 (placebo group) were given a corresponding volume of saline. In both groups, venous blood samples were collected for catecholamine, beta-endorphin, and cortisol assays before premedication and up to 72 hours after surgery. Postoperative pain was evaluated by measuring predefined behavioral and physiological variables. A total postoperative pain severity index (TPPSI) was calculated using all variables. There were no differences between PBZ and placebo groups in plasma beta-endorphin or catecholamine concentrations, but the TPPSI was higher in the placebo group than in the PBZ group, suggesting that perioperative treatment with PBZ has some analgesic benefit. This study shows the difficulties associated with pain assessment in horses.

Analgesic effects of butorphanol tartrate and phenylbutazone administered alone and in combination in young horses undergoing routine castration

“…In our study, there were no significant differences in heart rate, respiratory rate, or rectal temperature among the 3 treatment groups. Our findings are consistent with those of other studies 22,35,41,42 of physiologic indicators of postoperative pain in horses. Heart rate is affected by factors other than pain, including movement, eating, hydration status, and variations in sympathetic and parasympathetic tone.…”

“…21 Despite this fluctuation, plasma cortisol concentration has been useful for assessment of pain in horses. 35 However, in a clinical study 42 of horses that underwent arthroscopic surgery, plasma cortisol concentration was not a good indicator of pain. Serial measurements of plasma cortisol concentrations were performed before and after castration in our study to account for the individual characteristics of release and elimination of the hormone and to determine whether any changes were a result of the treatment.…”

A comparison of methods for evaluation of pain and distress after orthopaedic surgery in horses

“…In the study of Robertson et al (1990) plasma cortisol concentration was increased at the end of anaesthesia, but it had returned to baseline in samples taken 6 h after arthroscopic surgery in horses. In the study of Raekallio et al (1997) no significant increase was detected after the end of arthroscopic surgery in horses. Plasma cortisol has a diurnal rhythm in horses, reaching its highest concentrations in the morning and lowest in the evening (Zolovick et al 1966;Evans et al 1977;Larsson et al 1979).…”

Pain

“…6,18 These physiologic parameters, although easy to acquire and quantify, have been shown to have low sensitivity and specificity for pain in part because of multiple factors influencing these responses. For example, although pain may cause alterations in heart rate, other factors, such as shock, medications, stress, or exercise, may also be influential.…”

“…2,3 Recent interest has resulted in increasing knowledge and availability of objective measures for pain evaluation in horses. [4][5][6][7][8] Following a brief review of pain physiology, the focus of this article is on the tools available for the diagnosis and management of musculoskeletal pain and their consideration in developing rehabilitation protocols.…”