Before improving quality of life for patients, a veterinarian must first understand the cause of a decrease in quality of life. Pain is universally accepted as decreasing quality of life but is fairly ambiguously defined; according the International Association for the Study of Pain (IASP), pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.
Before improving quality of life for patients, a veterinarian must first understand the cause of a decrease in quality of life. Pain is universally accepted as decreasing quality of life but is fairly ambiguously defined; according the International Association for the Study of Pain (IASP), pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage. Given this the broad concept of pain, it is no wonder that applying a pain assessment tool seems daunting. However, the importance of monitoring and treating pain has gained prominence in veterinary medicine, with respected groups such as the American Animal Hospital Association (AAHA) issuing guidelines for inclusion of pain management in regular veterinary practice. Familiarity with pain assessment scales makes them more user friendly and easier to incorporate. This lecture will review some available pain assessment methods.
Because pain assessment is subjective, it stands to reason that some assessment tools are subjective as well. Simple descriptors have been used; however, there are is no standardization for descriptors. This lack of standardization means that while an assessor can describe pain in the present moment, that pain assessment is often unquantifiable, difficult to correlate between observers and difficult to contrast to previous or future painful episodes. Descriptors do have their place; in one study, owner assessment of pain was more accurate than the veterinarian's assessment when compared to objective data measurements of pain (Lascelles et al. 2008). Descriptors are fairly easy tools for owners to use, requiring little training or special skills for use. However, these tools are most useful if owners avoid emotional descriptors that are based in anthropomorphism, and instead focus on descriptors surrounding the individual pet's behavior. In the clinic setting, descriptors lose utility because of large interobserver variability. If a hospital chooses not to utilize a structured assessment tool, the staff should still be encouraged to approach the clinician in charge of a patient deemed painful, so the clinician can reassess the patient themselves and thus reduce the variability.
A structured assessment tool helps both at a clinical level and to advance the veterinary profession. Evidenced based medicine is difficult to practice when it comes to pain assessment, owing the large amount of variability between tools used for assessment. Structured assessment tools reduces the subjectivity of pain assessment, allowing for standardization between individuals as well as providing criteria for intervention and treatment, homogenizing the literature for ease of review, and performing outcome studies.
Physiologic variables are often assessed as indicators of pain because they lack subjectivity. Unfortunately, heart rate, respiratory rate, and temperature are poor indicators of pain; while a painful animal may have an increase in heart rate or respiratory rate, an animal with normal heart rate or respiratory rate is not necessarily pain free. Cortisol levels have utility in research pain assessments, but are poor patient side indicators because of the turnaround time to get this information back. Other indicators, such as pupillary size, might even be validated as useful in research settings, but are difficult to accept conceptually as useful pain indicators.
Several basic scales are used in the human medical field, such as the visual analogue scale, the numeric rating scale, and simple descriptive scale. These scales are more useful in a species that can verbalize their discomfort; in veterinary species, they have limited value, especially because they do not require interaction with the patient for score assignment. A dog post orthopedic surgery may look calm in its kennel, but be non-weight bearing when interacted with. So, although these tools are more structured than simple observations, they are not a gold standard for pain assessment.
Objective assessment measures are often used in research settings to allow for comparison between studies. For example, force plate analysis is often used to assess the degree of lameness and response to analgesia in orthopedic pain models. Force plate analysis records vertical, craniocaudal, and mediolateral forces, and braking, propulsion, and vertical impulses in a variety of models. These variables are then analyzed against a control to determine if there is deviation. Because the comparison control is often the contralateral limb of the same dog, or the same dog before and after induction of a disease condition, there is limited usefulness in the clinical patient. Likewise, other models of pain stimulus (such as mechanical or thermal) are used to assess pain expected to utilize these pathways, but rarely would be assessment tools in the clinical patient unless the animal could serve as it's own control; even then, studies use a certain number of patients in order to reduce the risk of individual variability. However, understanding this model allows interpretation of the literature, which may help us to make more appropriate clinical decisions.
At this point, it is clear that the most appropriate pain assessment tools would combine some subjective information that is stratified to have an objective quality. In an acute setting, this is often descriptors with an assigned score to various parameters. One tool, the Glasgow Composite Pain Scale (GCPS), has been validated (Morton et al. 2005). Validation ensures a tool is effective in testing or measuring the property being investigated. The GCPS uses four assessment parameters, with two of the four parameters being divided into two categories. Each of parameter or category is scaled zero to three through five, and each number has a descriptor. For example, in the first parameter of looking at the dog in the kennel, zero is quiet, one is crying or whimpering, two is groaning and three is screaming. The total is summed at the end (with highest value being 24) and if the value is greater than eight, the animal is considered painful. The GCPS has been validated against a variety of procedures, making it a useful tool for most acutely painful interventions. When one becomes familiar with this assessment, it generally takes less than 60 seconds to complete. Parameters include looking at the dog in the kennel, putting a lead on the dog and walking it out of the kennel, applying gentle pressure to the wound sight, and overall assessment of the dog.
There are other acute descriptor pain scales that have been developed, but validation is rare. Colorado State University's Veterinary Medical Center has patented pain scales in the cat, dog and horse; these are available on their website. These scales not only include a verbal descriptor with an associated score, but also include a picture of what an animal with the suggested score should look like. University of Melbourne also has a pain scoring system that has six parameters (physiologic data, response to palpation, activity, mental status, posture, and vocalization) which has descriptors with assigned numbers from zero to three. While a comprehensive scale, there are some odd things for inclusion on the scale; for example, dilated pupils scores a two, and a dog being overtly friendly scores a one (rather than zero). Ultimately, the veterinarian should test out a variety of pain scoring systems in their practice and find out what is the most user-friendly scale for them. Again, acute pain assessment, once used routinely should add little additional time to a busy day.
There are also several descriptor scales that have proved useful for chronic conditions, such as osteoarthritis. The Canine Brief Pain Index (CBPI) has been validated for assessment of osteoarthritis and bone cancer (Brown et al. 2009). The CBPI is composed of four pain severity questions scored on a scale of zero (no pain) to ten (extreme pain) and six pain interference questions (how much pain interfered with the a canine's function) scored from zero (does not interfere) to ten (completely interferes). This underscores the owners importance in helping to diagnosis and monitor pain. Another validated assessment scale for use in assessing pain due to osteoarthritis, the Helsinki Chronic Pain Index (HCPI) (Hielm-Björkman, Rita and Tulamo 2009), is a scale looking at 11 parameters that relate to an overall assessment of the animal, the animal in motion, and the animal's movement after rest/exercise. These were scored on a scale from zero (essentially what was most normal) to four (not at all). This scale appears very user friendly.
While not specifically looking at pain, several quality of life indicators for conditions such as cardiac disease and oncologic disease have been developed as well. Because pain negatively impacts quality of life, it would make sense that animals with a chronic condition might be assessed using such scales.
In summary, there are many tools with which pain is assessed, and familiarity with these tools opens the doorway to easily incorporating such tools into veterinary practice. The initial first step of pain recognition is critical helping veterinarians manage pain appropriately.
Brown, D. C., R. Boston, J. C. Coyne & J. T. Farrar (2009) A novel approach to the use of animals in studies of pain: validation of the canine brief pain inventory in canine bone cancer. Pain Med, 10, 133-42.
Hielm-Björkman, A. K., H. Rita & R. M. Tulamo (2009) Psychometric testing of the Helsinki chronic pain index by completion of a questionnaire in Finnish by owners of dogs with chronic signs of pain caused by osteoarthritis. Am J Vet Res, 70, 727-34.
Lascelles, B. D., J. S. Gaynor, E. S. Smith, S. C. Roe, D. J. Marcellin-Little, G. Davidson, E. Boland & J. Carr (2008) Amantadine in a multimodal analgesic regimen for alleviation of refractory osteoarthritis pain in dogs. J Vet Intern Med, 22, 53-9.
Morton, C. M., J. Reid, E. M. Scott, L. L. Holton & A. M. Nolan (2005) Application of a scaling model to establish and validate an interval level pain scale for assessment of acute pain in dogs. Am J Vet Res, 66, 2154-66.