Through a glass darkly: using behavior to assess pain.

Behavior assessment is crucial to the process of evaluation of pain and discomfort in veterinary patients. Behavioral responses to pain and other stressors are a function of the interaction between the individual and its environment, and are influenced by many factors including species, breed, age, sex, source of pain, and coexisting disease. Behavioral changes associated with acute postoperative pain typically peak within 24 hours and wane progressively thereafter. The intensity and duration of postoperative pain correlate with the location and extent of tissue injury, but there is much inter-patient variation of each characteristic. Published methods of systematic evaluation of pain in animals include objective measures of physiologic responses to experimental pain, subjective or semi-objective assessment of postoperative behavior, and quantitative measures of postoperative behavior and physiology. The techniques of quantitative measures of behavior are similar to pain-rating instruments developed for use in young children. Although objective assessment tools are difficult to develop and time consuming to apply, their methodological rigor and objectivity allow evaluation of behavior with minimal observer bias. Until objective assessment tools become widely used clinically, the best approach is to actively seek out evidence of pain in our patients, assuming its presence whenever there is tissue injury or inflammation.