Recognizing and assessing pain in cats (Proceedings)

Most recent estimates suggest there are over 80 million cats in the United States. Many of these cats will undergo a procedure expected to result in pain, underscoring the need for sound pain assessment tools. Additionally, the American Animal Hospital Association (AAHA) and the American Association of Feline Practitioners (AAFP) have published guidelines in 2007 for incorporating pain management into veterinary practice. The first and pivotal step in the algorithm is assessing whether or not the animal is in pain. However, feline behavior and temperament make pain difficult to assess. This lecture will review feline pain assessment tools for use in feline patients.

Pain is defined, by the International Association for the Study of Pain (IASP), as " an unpleasant sensory or emotional experience associated with actual or potential tissue damage, or described in terms of such damage". Pain experiences are unique to each individual, making standardization of assessment difficult, and leading traditionally a very subjective assessment of pain. Fear or stress behaviors are difficult to differentiate from those associated with pain. Understanding an individual patient's normal behavior is imperative and this makes owners' insight into their cats "normal" behavior critical. This information is most valuable when pain descriptors that reduce the possibility of anthropomorphism are selected. Questions should be structured to assess changes in behavior, with the owner providing information into key behaviors for their pet (e.g. food motivation, grooming, certain resting spots) as opposed to open-ended questions where interpretation of the cat's psychological state is more likely. Additionally, if there are multiple observers, simple subjective descriptors of pain are unlikely to have the same meaning to each observer, demonstrating the necessity for a more objective assessment of pain.

A structured assessment tool allows a veterinarian to evaluate baseline pain and to monitor response to therapy. The necessary components of this tool include being user friendly, accurate, reliable and time-efficient. Some of the simplest forms of assessment include simple descriptive scales, numeric rating scales, and visual analogue scales. These tools are easy to use, but have only one dimension to them, do not account for interaction with the patient, and vary greatly between observers. Physiologic data is easy to collect, and is more objective than simple observation. However, there is poor correlation between objective physiologic information (e.g. heart rate and respiratory rate) and observed behaviors in animals following surgery. Several studies have indicated that blood pressure is a useful indicator of post-operative pain, but only in the early postoperative period (Brondani, Luna and Padovani 2011). Cortisol levels provide objective data that may be useful in assessing pain in a research setting, but the lack of bedside availability limits clinical usefulness.

When reviewing relevant literature on feline pain, the methods of assessment described vary in their objectiveness. Several nociceptive threshold-testing devices are adapted for use in cats, but are frequently limited to a laboratory setting to assess analgesic drugs for onset, intensity and duration of antinociceptive actions (i.e. before clinical testing is performed). Feline models of pain have included thermal, mechanical, electrical and visceral stimulation. These methods of stimulation are not practical for a clinical setting, however.

Perhaps the most logical approach for assessing feline pain comes from combining a subjective assessment, such as behavior, with a scoring indicator (e.g. a scale from zero to five); assigning a descriptor as well as a score facilitates reproducibility and consistency of scoring. For example, under the descriptor "posture", descriptors such as relaxed, hunched and rigid have corresponding scores from zero to three. Response to palpation of a surgical or traumatic wound is a useful indicator of pain. This response may be mild or may elicit a defensive behavior from the cat. In some cases, a cat may preemptively anticipate pain when being handled, perhaps from fear rather than pain itself, but assessing a patient prior to an procedure expected to cause pain will help the veterinarian to determine whether this assessment is useful. In the compliant patient, it is possible to apply pressure over a wound and the surrounding area without the patient resenting it (when pain has been adequately addressed).

One of the first scales validated in feline pain assessment has been published recently (Brondani et al. 2011). This scale is only validated in cats undergoing ovariohysterectomy, but gives a range of items to consider when deciding if a feline patient is painful; these include assessment of posture, comfort, activity, mental status, reaction to palpation both of the surgical area and in general, appetite, systolic blood pressure, and vocalization. Brondani's pain scale is particularly easy to use in that it retains value for pain assessment even if categories must be removed, with the more categories assessed enhancing (but not essential) for pain assessment. Although not validated, Colorado State University also has a pain scale for use in feline pain assessment that is user friendly.

Facial expression is undergoing examination by researchers such as Robertson et al as an assessment tool. Initial data would indicate painful cats hold their head low with their eyes fully or half shut with a slanted angle.

The pain scale developed by Brondani highlights the importance of timing in the assessment of pain. Intuitively, it makes sense to assess a patient before a painful event. However, Brondani et al were able to demonstrate that some indicators of pain were present only in the immediate post-operative period instead but not 24 hours later. Whether this reflects a cat's adaptation to pain or a decrease in pain with time, it changes our assessment as time progresses.

There is interest in assessment of pain in feline osteoarthritis, a disease condition which affected 61% of cats examined in one study (Slingerland et al. 2011). For such a prevalent disease, there is little information on assessment. In the dog, assessment tools, such as the Canine Brief Pain Index, which tailors assessment to the specific animal and appears helpful in osteoarthritis cases. Quality of life indicators for cats for chronic conditions, such as aging and cardiac disease, have been developed. While not specifically addressing pain, these scales help with overall assessment of a feline patient's well being (Reynolds et al. 2010, Pittari et al. 2009).

Our goal of assessment is to provide a stepping-stone to effective analgesic therapy. While this assessment is (by virtue of application to a non-verbal species) subjective, scales are available to practitioners with some measure of objectivity to them. A foundation of pain assessment will assist with future advancement in feline analgesia.

References

Brondani, J. T., S. P. Luna & C. R. Padovani (2011) Refinement and initial validation of a multidimensional composite scale for use in assessing acute postoperative pain in cats. Am J Vet Res, 72, 174-83.

Pittari, J., I. Rodan, G. Beekman, D. Gunn-Moore, D. Polzin, J. Taboada, H. Tuzio & D. Zoran (2009) American association of feline practitioners. Senior care guidelines. J Feline Med Surg, 11, 763-78.

Reynolds, C. A., M. A. Oyama, J. E. Rush, E. A. Rozanski, G. E. Singletary, D. C. Brown, S. M. Cunningham, P. R. Fox, B. Bond, D. B. Adin, R. M. Williams, K. A. MacDonald, R. Malakoff, M. M. Sleeper, K. E. Schober, J. P. Petrie & D. F. Hogan (2010) Perceptions of quality of life and priorities of owners of cats with heart disease. J Vet Intern Med, 24, 1421-6.

Slingerland, L. I., H. A. Hazewinkel, B. P. Meij, P. Picavet & G. Voorhout (2011) Cross-sectional study of the prevalence and clinical features of osteoarthritis in 100 cats. Vet J, 187, 304-9.