Pain: assessment

Introduction

• One of the main goals of all those dedicated to working with animals is to relieve their pain. The benefits of pain management are numerous and many safe and effective analgesic drugs and treatment modalities are now available for use in dogs and cats.
• However, in order to treat pain we must first recognize it. Assessment of pain in animals is not an easy task but is essential to ensure our plan is effective.
• Pain is a complex multidimensional experience involving both sensory and affective (emotional) components. It is now accepted that animals do experience pain even if they cannot communicate it in the same way humans do (Paul-Murphy J et al, 2004). Pain is a subjective and individual experience and humans show large inter-individual differences in quality, intensity and response to intervention which are genetically determined (Montagna P, 2007) and this is likely true in animals. Certainly, individual variation in response to opioids has been documented in cats (Lascelles B D & Robertson S A, 2004).
• In animals, pain is what the observer says it is and because all judgments are subjective if we get it wrong, animals will suffer. The issue in animals is complex because we must consider differences in age, species, breed, and environment. Assessment systems must also take into account the different types and sources of pain, such as acute versus chronic or neuropathic pain, and visceral compared to somatic pain. In a clinical setting, there are no accurate objective measures of pain, such as heart rate, blood pressure or plasma cortisol levels (Conzemius M G et al, 1997; Cambridge A J et al, 2000; Smith J D et al, 1999) which is not surprising since these variables can be affected by many factors including fear and stress. Therefore pain assessment in animals must be based on behavior; either changes in, or loss of normal behaviors (eg grooming in cats) or the display of new behaviors (eg aggression in a previously friendly dog). Behavioral responses to pain vary greatly between species and even within a species. Few veterinarians would disagree that Labradors react differently to the Arctic breeds in the post-operative period. Ideally we must know the individual animals normal behavior and for this reason people who spend most time with the dog or cat, are invaluable in the assessment process; this is often the owner or veterinary nurses.
• At this time there is no gold standard for assessing pain in animals, and it is obvious from the work of Holton and others (Holton L et al, 2001) with dogs that creating meaningful pain assessment tools is a painstaking and time-consuming task. In a recent survey only 8.1% of practices were using a pain scoring system yet 80.3% of veterinary nurses agreed they are useful clinical tools (Coleman D L & Slingsby L S, 2007). The key question for a busy practitioner is how well do the available scoring systems perform in clinical practice? and what behaviors are most likely linked to pain.

Sources

Publications

Refereed papers

• Recent references from PubMed.
• Coleman D L & Slingsby L S (2007) Attitudes of veterinary nurses to the assessment of pain and the use of pain scales. Vet Rec 160 (16), 541-544 PubMed.
• Lascelles B D et al(2007) Evaluation of client-specific outcome measures and activity monitoring to measure pain relief in cats with osteoarthritis. J Vet Intern Med 21 (3), 410-416 PubMed.
• Montagna P (2007) Recent advances in the pharmacogenomics of pain and headache. Neurol Sci 28 Suppl 2, S208-212PubMed.
• Waran N et al(2007) A preliminary study of behaviour-based indicators of pain in cats. Animal Welfare 16 (S), 105-108.
• Wiseman-Orr M L et al(2006) Validation of a structured questionnaire as an instrument to measure chronic pain in dogs on the basis of effects on health-related quality of life. Am J Vet Res 67 (11), 1826-1836PubMed.
• Yazbek K V & Fantoni D T (2005) Validity of a health-related quality-of-life scale for dogs with signs of pain secondary to cancer. J Am Vet Med Assoc 226 (8),1354-1358 PubMed.
• Lascelles B D & Robertson S A (2004) Use of thermal threshold response to evaluate the antinociceptive effects of butorphanol in cats. Am J Vet Res 65 (8), 1085-1089 PubMed.
• Paul-Murphy J et al(2004) The need for a cross-species approach to the study of pain in animals. J Am Vet Med Assoc 224 (5), 692-697 PubMed.
• Wiseman-Orr M L et al(2004) Development of a questionnaire to measure the effects of chronic pain on health related quality of life in dogs. American Journal of Veterinary Research 65 (8), 1077-1084 PubMed.
• Holton L et al(2001) Development of a behaviour-based scale to measure acute pain in dogs. Vet Rec 148 (17), 525-531 PubMed.
• Slingsby L, Jones A & Waterman-Pearson A E (2001) Use of a new finger-mounted device to compare mechanical nociceptive thresholds in cats given pethidine or no medication after castration. Res Vet Sci 70 (3), 243-246 PubMed.
• Wiseman M L et al(2001) Preliminary study on owner-reported behaviour changes associated with chronic pain in dogs. Vet Rec 149 (14), 423-424 PubMed.
• Cambridge A J et al(2000) Subjective and objective measurements of postoperative pain in cats. J Am Vet Med Assoc 217 (5), 685-690 PubMed.
• Smith J D, Allen S W & Quandt J E (1999) Changes in cortisol concentration in response to stress and postoperative pain in client-owned cats and correlation with objective clinical variables. Am J Vet Res 60 (4), 432-436 PubMed.
• Holton L L et al(1998) Comparison of three methods used for assessment of pain in dogs. J Am Vet Med Assoc 212 (1), 61-66 PubMed.
• Lascelles B et al(1998) Efficacy and kinetics of carprofen, administered preoperatively or postoperatively, for the prevention of pain in dogs undergoing ovariohysterectomy. Vet Surg 27 (6), 568-582 PubMed.
• Conzemius M G et al(1997) Correlation between subjective and objective measures used to determine severity of postoperative pain in dogs. J Am Vet Med Assoc 210 (11), 1619-1622 PubMed.
• Vesal N, Cribb P H & Frketic M (1996) Postoperative analgesic and cardiopulmonary effects in dogs of oxymorphone administered epidurally and intramuscularly, and medetomidine administered epidurally: a comparative clinical study. Vet Surg 25 (4), 361-369 PubMed.