Correlation between subjective and objective measures used to determine severity of postoperative pain in dogs

Objective - To determine the association between subjective and objective variables commonly used to evaluate severity of postoperative pain in dogs. Design - Prospective double-blind study. Animals - 36 dogs with unilateral rupture of the cranial cruciate ligament that underwent surgery to stabilize the stifle. Procedure - Each dog was assessed to determine severity of pain before and after surgery, using various subjective and objective criteria. Results - Subjective measures of pain (scores for visual analogue and numerical rating scales) correlated poorly or were not correlated with heart rate, respiratory rate, blood pressure, and results of a pain threshold test. Scores for visual analogue and numerical rating scales correlated with each other and with the amount of vocalization at most time periods. Clinical Implications - We detected a weak association between commonly employed subjective and objective measures of pain. This indicated that some of these measurement techniques do not predictably reflect severity of postoperative pain in dogs. Therefore, clinicians should not rely too heavily on these variables when assessing severity of postoperative pain in dogs.