Pain assessment in companion small animals (Proceedings)
Nov 01, 2009
CVC IN SAN DIEGO PROCEEDINGS
The challenge of pain assessment in animals lies in the very concept of pain itself. The International Association for the Study of Pain defines pain as "an unpleasant sensory or emotional experience associated with actual or potential tissue damage". Given that definition, how is one to interpret what an animal might determine is unpleasant? Or how is a human observer to determine the extent of a non-verbal animal's emotional response to anticipated or actual tissue injury? Pain is a perception and the experience of pain in any individual animal or human being has no definitive physical dimensions and is subject to extremely complex sensory and cortical processing. There is a long road (upon which things happen fast!) between the event of tissue injury and the outcome of pain perception by the animal, and along this road many factors determine the animal's perception of pain, not the least of which are peripheral and spinal cord sensory modulation, cerebral cortical processing, learned behavior, and anxiety. All of these factors may play into the animal's perception and response to pain. As veterinarians, we impose upon our patients our own human interpretation of animal behaviors that we may suppose suggest pain. We have no way of determining the animal's actual perception of the degree of pain that it is experiencing at that moment: we simply intuit behavior and overlay that with our own experience of pain in ourselves or with our prior experience to "measure" that animal's pain.
A relatively anthropomorphic approach to pain assessment in animals seems appropriate when one considers that peripheral and spinal cord sensory systems are almost identical between humans and non-human mammals. Pain perception, however, occurs in the prefrontal cortex and this area is anatomically smaller in non-human mammals. This does not necessarily mean that pain perception is different in animals, simply that we do not know how they interpret or perceive peripheral pain. A sensible approach is to start by assuming that if an observed disease state or tissue injury or surgical procedure would be painful to you, as a veterinarian, then it likely is painful to the animal to a similar degree. This approach must be taken in the context of extensive and thorough observation of the animal, its response to analgesic treatment, and the expected time course of the waxing and waning of the expected pain.