Pain scales and scoring in clinical settings: part 2

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Vet Times The website for the veterinary profession https://www.vettimes.co.

1 Vet Times The website for the veterinary profession Pain scales and scoring in clinical settings: part 2 Author : Rebecca Robinson Categories : Companion animal, Vets Date : March 7, 2016 A shift has been made in the attitudes towards animal pain. It is accepted animals feel pain, so there is a requirement for analgesia provision for livestock, companion and laboratory animals undergoing painful procedures. Table 1. Physiological effects of pain. Working within the veterinary profession, we have a moral obligation to ensure animals under our care receive appropriate analgesia. Additionally, untreated pain can result in significant delays in a return to normality with multiple physiological effects. 1 / 13

2 Management of acute, postoperative pain in companion animals was discussed in VT However, to successfully manage pain in non-verbal species, confidence in assessment is required, in terms of its absolute presence or absence and its severity. This allows an appropriate level of analgesia to be promptly administered and the required dosing frequency to be judged. Using standardised pain scales allows a repeatable measure that is consistent between observers. Additionally, if the pain score is recorded over time, it allows an objective evaluation of a patient s response to management. Difficulties of assessing animal pain Pain is considered to be a subjective experience; therefore, what might be painful for one individual might not be for another. In verbal humans this problem is overcome by asking the individual to self-report. This becomes difficult when dealing with non-verbal beings, including neonatal humans or veterinary species. It falls to the carer to recognise and interpret signs of pain, which requires a certain level of skill and knowledge. Table 1 illustrates the numerous physiological changes associated with pain. However, these changes are not specific to pain, so we cannot rely solely on such variables. In a laboratory setting it is possible to use neurophysiological techniques (Murrell and Johnson, 2006) and measurement of plasma hormone concentrations (such as cortisol or acute phase proteins), with varying degrees of success depending on the method employed, type of pain and species. In clinical practice, pain assessment primarily involves recognition of behavioural alterations. This includes loss of normal behaviours and development of new ones (Table 2). It is, therefore, critical any assessor is aware of normal behaviour for the specific species (Figure 1). This is particularly important when assessing prey species, such as rodents that do not often show overt signs associated with pain, unlike the vocalisation or aggression by dogs. Numerous factors may contribute to our poor pain recognition in these species, including how long humans have co-evolved with the species and whether overt signs of pain are likely to increase assistance from social group members or the risk of predation. 2 / 13

All of these are indicators of pain in cats. Figure 1b.

3 Figure 1a. Behavioural indicators are an important aspect of pain assessment, but one must be aware of the normal behaviour for species. This cat is recumbent, tense and unwilling to move. Note the facial expression with half-closed or squinting eyes. All of these are indicators of pain in cats. Figure 1b. Behavioural indicators are an important aspect of pain assessment, but one must be aware of the normal behaviour for species. This cat looks relaxed with its feet curled under the body and the head up. The cat looks alert and the eyes are held wide open. 3 / 13

4 Pain assessment in non-verbal species can be complicated by external factors. The presence of environmental or situational stressors can modulate the patient s response to pain. Administration of sedative drugs as part of a perianaesthetic protocol may mask behavioural changes associated with pain. In humans, the pain response can be amplified by anxiety, causing hyperalgesia (Colloca and Benedetti, 2007). A similar scenario may possibly occur in veterinary species. Observer-specific factors, including age, gender, clinical experience, previous personal experience and time since graduation, can influence the overall pain assessment. For example, when laboratory mice are assessed by male as opposed to female observers, the male scent causes a stress response, resulting in stressinduced analgesia and fewer pain-induced behavioural changes (Sorge et al, 2014). Such phenomena will ultimately influence both the type and frequency of analgesia provision. Types of pain scales A number of different pain scales have been developed for use, most adapted from those for human medicine. A key difference between human and veterinary pain scales is in veterinary medicine all are based on observer interpretation of the intensity of the animal s pain. For maximal patient benefit, it is crucial only one pain scale is used throughout treatment. This allows assessment of the patient s response to analgesic therapy and can guide future treatment. Changing between types of pain scales for individual patients is not advised, as the variation will prevent temporal comparison. Visual analogue scale A visual analogue scale (VAS) consists of a horizontal line, normally 100mm in length. The zero end of the scale represents no pain while 100mm represents the worst pain imaginable (Figure 2). The observer marks this line corresponding to their perception of the animal s pain. This can be quantified by measuring the distance in millimetres from zero. Arbitrary cut-off values can be set for determining analgesia administration. Studies in human medicine suggest values lower than 35mm are consistent with mild pain, while above this value pain becomes progressively more severe (Boonstra et al, 2014). Regular, repeated assessment and recording of values allows response to analgesia to be determined. 4 / 13

Table 2. Possible behavioural effects of pain. Although simplistic and rapid to use, some degree of training is required for use, as observers need to be familiar with pain behaviours.

5 Table 2. Possible behavioural effects of pain. Although simplistic and rapid to use, some degree of training is required for use, as observers need to be familiar with pain behaviours. When used repeatedly by the same observer, VAS shows good reproducibility. However, if multiple people are involved in pain assessment there is significant interobserver variability (Holton et al, 1998), reducing their usefulness and having implications for analgesia provision in clinical settings. Numerical rating scale 5 / 13

6 Numerical rating scales (NRS) are comparable to VAS, with similar caveats, although the scale is drawn with discrete numbers, from zero to 10, on the illustrated line (Figure 1). As with a VAS scale, zero represents no pain and 10 represents the worst pain imaginable. Such a system may have a reduced sensitivity compared to VAS, as only whole integers are used. Simple description scales Simple description scales (SDS) have many parallels to NRS, the difference being that descriptors, rather than numbers, are used. Such descriptors may be linked to a number to convert the result to a pain score. A widely used example in human medicine for ages three and older is the Wong-Baker FACES pain rating scale (Figure 3). The diagrammatic and descriptive representation makes it easier to understand and self-report. Similar scales have been adapted for veterinary patients, including those produced by Colorado State University, using multiple SDS to assess acute pain in cats, dogs and horses (Colorado State University, 2006b; Colorado State University, 2007). Dynamic interactive visual analogue scale Dynamic interactive visual analogue scale (DIVAS) is an expanded version of the VAS. It uses the same principle of marking the perceived pain level along a 100mm line. However, DIVAS also relies on the handler interacting with the patient and gently palpating surgical wounds to provide a complete score. Multi-dimensional composite pain scales VAS and NRS are considered unidimensional, as they only assess pain intensity. However, as Tables 1 and 2 show, pain affects an animal in multiple ways; therefore, multidimensional composite scales have been developed to incorporate such factors, assessing not only the physical pain intensity, but also emotional effects. Such scales often weigh behaviours and variables differently, which may help to minimise the interobserver variability seen with more basic scales. Some multidimensional composite pain scales take account of both physiological and behavioural aspects while some focus primarily on behavioural changes, usually with and without handler interaction. As with other pain scales, these rely on user experience of normal behaviour for the particular species. The short form of the Glasgow composite measure pain scale for canine acute pain is probably the best known multidimensional pain scale. This was preceded by the University of Melbourne s pain scale (Firth and Haldane, 1999). 6 / 13

7 Figure 2a. Visual analogue scale. Figure 2b. Numerical rating scale. 7 / 13

Figure 3. The Wong-Baker FACES pain rating scale a simple descriptive scale for assessment of pain in humans. Used with permission from www.wongbaker FACES.

8 Figure 3. The Wong-Baker FACES pain rating scale a simple descriptive scale for assessment of pain in humans. Used with permission from FACES.org Pain faces There is a growing amount of research and evidence assessing how facial expressions change when an animal is in pain. This has been a well-known method of pain assessment in rats and mice in laboratory settings for many years, with the rat grimace scale and mouse grimace scale including assessment of the tightening of the orbital area, flattening of the nose and cheek, and changes in the ear and whisker position (Sotocinal et al, 2011; Matsumiya et al, 2012; Oliver et al, 2014). Research is being performed to develop similar methods for species such as horses (Dalla Costa et al, 2014; Gleerup et al, 2015), rabbits (Keating et al, 2012) and cats (Holden et al, 2014). Validation Table 3. Three aspects requiring assessment to ensure validity of a pain scale. Pain scales can either be non-validated or validated. The process of validation involves extensive testing of the pain scale to ensure it is reliable, giving expected results, including those across different patients and users (Brondani et al, 2013). The process of validation assesses three aspects (Brondani et al, 2011; Table 3). Validating veterinary pain scales can be difficult, particularly for content validity (by relying on what has deemed to be important by experts) and criterion validity (a lack of gold standard methods of assessing pain). 8 / 13

9 In most cases, particular pain scales have been validated only for specific species and, in some instances, only for certain conditions or scenarios. Using a validated pain scale provides more consistent and accurate results, allowing easier comparison between subjects and clinical studies. Acute versus chronic pain scales The pathophysiology of acute and chronic pain differs greatly. Acute pain is generally caused by injury and often serves a protective or biological purpose. It is usually self-limiting and associated with the timescale of normal healing. Chronic pain, however, is often considered a disease state in its own right, doesn t serve any biological purpose and has no recognisable end point (Grichnik and Ferrante, 1991). Both the nature of the two pain states and their behavioural indicators are different. Therefore, pain scales designed for acute or chronic pain are not interchangeable. Acute pain scales are often designed for use by veterinary personnel in a hospital environment, as this is where acute pain is most likely to be experienced. Although it is always beneficial to know the pain-free behaviour of the animal, it is possible for a naïve observer/handler who has knowledge of the general species behaviour to use an acute pain scale to judge the level of pain. In contrast, behavioural changes associated with chronic pain can often be subtle and gradual in onset. As a result, such alterations can only be recognised by someone who is very familiar with the animal, usually the owner (Mathews et al, 2014). However, sometimes owners are unaware subtle changes may be associated with pain and often it is only highlighted when there is an improvement in patient demeanour during an analgesia trial. Chronic pain scales revolve around quality of life questionnaires and functional assessment of the animal. Factors considered often include: mobility daily activity levels interest in food and water grooming behaviour changes in temperament and demeanour (Brown et al, 2007; Hielm-Björkman et al, 2009; Mathews et al, 2014) Ocular pain 9 / 13

Figure 4. A dog with left ocular pain. Severe blepharospasm was present with a concurrent ocular discharge. The dog resented gentle palpation in the area surrounding the left eye.

10 Figure 4. A dog with left ocular pain. Severe blepharospasm was present with a concurrent ocular discharge. The dog resented gentle palpation in the area surrounding the left eye. Patients with pain caused by ocular conditions are particularly challenging to assess. Clinical signs, such as serous ocular discharge and photosensitivity, may be associated with the underlying condition, but not necessarily pain. Conversely, other clinical signs, such as blepharospasm, are often indicative of acute ocular pain (Figure 4). Assessment can become more difficult with ocular conditions likely to cause chronic pain, such as glaucoma. None of the veterinary acute pain scales are specific to ocular pain. However, a number of publications have used non-validated pain scales to assess ocular pain (Myrna et al, 2010; Clark et al, 2011). Validated pain scales A limited number of validated pain scales are available for companion animal use and may be for use in specific scenarios. Canine acute pain Short form of the Glasgow composite measure pain scale (Morton et al, 2005). Validated for assessment of acute pain associated with multiple conditions in dogs through a questionnaire completed by veterinary personnel. 10 / 13

11 Canine chronic pain Liverpool osteoarthritis in dogs scale (Hercock et al, 2009; Walton et al, 2013) Canine brief pain inventory (Brown et al, 2007; Brown et al, 2008; PennVet, 2006) Helsinki chronic pain index (HCPI; Hielm-Björkman et al, 2009; University of Helsinki (2012) All three have been validated for chronic pain associated with osteoarthritis through the use of owner questionnaires. The HCPI also uses a questionnaire completed by the veterinary surgeon. Feline acute pain São Paulo State University (UNESP) Botucatu multidimensional composite pain scale (Brondani et al, 2013; Animal Pain). Validated for pain assessment in cats postovariohysterectomy via a questionnaire completed by veterinary personnel. Glasgow composite measure pain scale feline (Calvo et al, 2014; Holden et al, 2014; NewMetrica). Validated for acute pain assessment in cats via a questionnaire completed by veterinary personnel. Work is ongoing to define the analgesia intervention level. Conclusion Assessing pain in veterinary species can be challenging. Pre-existing knowledge of normal speciesspecific behaviour is essential. Pain scales enable a more objective assessment of pain and allow serial assessments to be compared. Regular, repeated assessments with the same scale are required to determine if there has been a positive response to analgesia provision and to guide further therapy. Use of appropriate pain scales can help improve animal welfare in an acute, postoperative setting and animal quality of life during chronic pain states. Postoperative and acute pain management: part 1 (VT46.07) References Animal Pain. Boonstra AM et al (2014). Cut-off points for mild, moderate, and severe pain on the visual analogue scale for pain in patients with chronic musculoskeletal pain, Pain 155(12): 2,545-2, / 13

12 Brondani JT et al (2011). Refinement and initial validation of a multidimensional composite scale for use in assessing acute postoperative pain in cats, Am J Vet Res 72(2): Brondani JT et al (2013). Validation of the English version of the UNESP-Botucatu multidimensional composite pain scale for assessing postoperative pain in cats, BMC Vet Res 9:143. Brown DC et al (2008). Ability of the canine brief pain inventory to detect response to treatment in dogs with osteoarthritis, J Am Vet Med Assoc 233(8): 1,278-1,283. Brown DC et al (2007). Development and psychometric testing of an instrument designed to measure chronic pain in dogs with osteoarthritis, Am J Vet Res 68(6): Calvo G et al (2014). Development of a behaviour-based measurement tool with defined intervention level for assessing acute pain in cats, J Small Anim Pract 55(12): Clark JS et al (2011). Evaluation of topical nalbuphine or oral tramadol as analgesics for corneal pain in dogs: a pilot study, Vet Ophthalmol 14(6): Colloca L and Benedetti F (2007). Nocebo hyperalgesia: how anxiety is turned into pain, Curr Opin Anaesthesiol 20(5): Colorado State University (2006a). Feline acute pain scale, Colorado State University (2006b). Canine acute pain scale, Colorado State University (2007). Equine comfort assessment scale, Dalla Costa E et al (2014). Development of the horse grimace scale (HGS) as a pain assessment tool in horses undergoing routine castration, PLoS One 9(3): e Firth AM and Haldane SL (1999). Development of a scale to evaluate postoperative pain in dogs, J Am Vet Med Assoc 214(5): Gleerup KB et al (2015). An equine pain face, Vet Anaesth Analg 42(1): Grichnik KP and Ferrante FM (1991). The difference between acute and chronic pain, Mt Sinai J Med 58(3): Hercock CA et al (2009). Validation of a client-based clinical metrology instrument for the evaluation of canine elbow osteoarthritis, J Small Anim Pract 50(6): Hielm-Björkman AK et al (2009). Phychometric 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(6): Holden E et al (2014). Evaluation of facial expression in acute pain in cats, J Small Anim Pract 55(12): Holton LL et al (1998). Comparison of three methods used for assessment of pain in dogs, J Am Vet Med Assoc 212(1): Keating SC et al (2012). Evaluation of EMLA cream for preventing pain during tattooing of rabbits: changes in physiological, behavioural and facial expression responses, PLoS One 7(9): e Mathews K et al (2014). Guidelines for recognition, assessment and treatment of pain: WSAVA global pain council members and co-authors of this document, J Small Anim Pract 12 / 13

13 Powered by TCPDF ( 55(6): E Matsumiya LC et al (2012). Using the mouse grimace scale to reevaluate the efficacy of postoperative analgesics in laboratory mice, J Am Assoc Lab Anim Sci 51(1): Morton CM et al (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(12): 2,154-2,166. Murrell JC and Johnson CB (2006). Neurophysiological techniques to assess pain in animals, J Vet Pharmacol Ther 29(5): Myrna KE et al (2010). Effectiveness of injection of local anesthetic into the retrobulbar space for postoperative analgesia following eye enucleation in dogs, J Am Vet Med Assoc 237(2): NewMetrica. Instruments to measure acute pain, Oliver V et al (2014). Psychometric assessment of the rat grimace scale and development of an analgesic intervention score, PLoS One 9(5): e PennVet (2006). Canine brief pain inventory, Sorge RE et al (2014). Olfactory exposure to males, including men, causes stress and related analgesia in rodents, Nat Meth 11(6): Sotocinal SG et al (2011). The rat grimace scale: a partially automated method for quantifying pain in the laboratory rat via facial expressions, Mol Pain 7: 55. University of Helsinki (2012). The Helsinki chronic pain index, Walton MB et al (2013). Evaluation of construct and criterion validity for the Liverpool osteoarthritis in dogs (LOAD) clinical metrology instrument and comparison to two other instruments, PLoS One 8(3): e / 13

Why should I pain score? Kate White MA Vet MB, DVA, DiplECVAA, MRCVS

Why should I pain score? Kate White MA Vet MB, DVA, DiplECVAA, MRCVS Pain scoring Analgesics are still used sparingly by vets and owners Is this due to lack of recognition of pain? Pain scoring should