Effective Use of Pain Metrics

Using validated metrics, the assessment of pain provides a window for recognition of pain and more effective pain management, providing better quality data for the benefit of our patients and addressing the need for evidence-based advancement of veterinary medicine.

 

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Pain Scales Help Give Animals a Voice

“Dying is nothing, but pain is a very serious matter.”
—Henry Jacob Bigelow, 1871

Our foremost medical responsibility is to relieve suffering. Pain is at the forefront of clinical presentations for human patients and presumably would be for nonhuman animals if our patients could speak for themselves. But of course, they cannot. In extreme situations, pain alleviation is more important than maintaining life itself.

Pain that goes beyond the essential warning of the injured individual becomes deleterious. Maladaptive pain is a more meaningful contemporary term for chronic pain, which is any pain that lasts longer than the underlying pathology or is manifest in excess proportion to the injury. Maladaptive pain becomes a self-supporting deleterious syndrome and is more difficult to alleviate than initial, acute, or adaptive pain.

Quantitative assessment is vital in recognizing pain, suffering, and changes in the quality of life.

One of AAHA’s pain management–related standards mandates that “pain assessment using a standardized scale or scoring system is to be recorded in the medical record for every patient evaluation.” Among the approaches utilized are traditional physiologic measurements like temperature, pulse, and respiration (TPR); other physiological parameters; quantitative sensitivity measurements (pin algometer or von Frey filaments); and a wide variety of pain scales. Currently, these pain scales are based primarily on subjective observer-rated scoring of changes in specific behaviors.

The Role of Pain Scales

Using validated metrics, the assessment of pain provides a window for recognition of pain and more effective pain management, providing better quality data for the benefit of our patients and addressing the need for evidence-based advancement of veterinary medicine. Pain is recognized to be a “vital sign.” Patient evaluation based on vital signs in veterinary medicine usually includes temperature, pulse rate or heart rate, respiratory rate, and pain. Occasionally, arterial blood pressure is included, usually in anesthesia and critical care. These physiologic parameters and several biochemical and neurochemical markers—including epinephrine, norepinephrine, beta-endorphins, and cortisol—are better correlated to stress than to pain, but they can be helpful in scoring based primarily on changes in specific behaviors.

Species-Specific Chronic Pain Behaviors

Dogs—decreased mobility; however, eating behavior is rarely affected

Cats—isolation from others in the household, decreased grooming, and cessation of eating

Horses—inappetence, severe weight loss, dull expression, glazed eyes, and base-wide stance

Ruminants—weight loss and isolation from the herd

Pigs—reluctance to rise, reduced social interaction, and little appetite change

As medical providers, our obligation to relieve pain and suffering is paramount, yet often we are in the dark. Veterinary personnel and animal owners are notoriously inaccurate in recognizing signs of pain in animals. Animals presented to veterinary hospitals are most often fearful, stressed, and anxious, and they usually will not display the specific behaviors signaling pain that they would in their typical home environment. Our clients often mistake pain for what they believe is just a progression of normal aging changes. Animal owners are often ignorant because they just don’t know what to look for as behavioral signs of pain. But, because they know the normal behavior, they can learn to identify specific changes and share relevant observations with us. With the provision of compassionate education on the several behavioral changes indicative of pain, our clients can become our most essential partners in recognizing and managing pain in their animals.

Scientific principles teach us that we cannot understand until we can measure. We must have some metrics, especially validated metrics, to guide our patient care. Quantitative assessment is vital in recognizing pain, suffering, and changes in the quality of life. Assessment guides analgesic therapies in that clinical providers can follow the success or failure of treatment plans through changes in the validated metrics over time. Assessment metrics are also essential in developing and validating new analgesic therapies.

Pain is a highly individual experience, influenced by many intrinsic and extrinsic factors. The gold standard for assessing pain in humans is the self-report, most often using a numeric rating scale, which, of course, animals are not capable of providing. Many pain scales and scoring systems have been developed and validated for our subjective observer-rated assessment of acute and chronic pain in animals; these are called clinical metrology instruments. This short article mentions a few of the pain scales and pain-scoring systems used in veterinary medicine and suggests readily available resources to aid in assessing pain.

Tools and Best Practices

Repeated evaluations by the same person, if possible, are most valuable while following a course of therapy. Conducting an interactive pain evaluation and establishing a pain score before and after treatment helps develop and refine the best pain management plan. Assessment and scoring are especially helpful in determining the choices of analgesics, dosage levels, routes of administration, and treatment intervals. Behavioral assessment and pain scoring are best completed by those most familiar with the patient’s normal behavior—the owners—in the home environment.

Assessments of pain in animals should include an interactive component. Many subjects will hide signs of pain or remain atypically inactive until stimulated by interaction with other animals or human evaluators. A cautious and graded approach and interaction are required. Increasing or exacerbating existing pain can inadvertently increase fear, anxiety, stress, and aggression, compounding the impact of pain. The patient’s temperament may influence our scores, as may our inherent human bias in recognizing and ascribing significance to vocalization over nonverbal communication. Caution and respect for the potential of painful animals to respond to even gentle interactive examination with aggression are essential for the benefit of both patients and veterinary personnel. If our patient interaction and evaluation in conducting pain assessment inadvertently cause or exacerbate pain, our patients may bite, scratch, or otherwise share the pain with us!

Among several essential references, the 2015 AAHA/AAFP Pain Management Guidelines (and the soon-tobe-released 2022 AAHA Pain Management Guidelines for Dogs and Cats) emphasize the value of behavioral indices for the observer-rated assessment of animal pain. The 2022 International Society of Feline Medicine Consensus Guidelines on the Management of Acute Pain in Cats focus attention on pain assessment, with due emphasis on the importance of our client’s role in observation and evaluation. In addition, the World Small Animal Veterinary Association issued “Guidelines for Recognition, Assessment, and Treatment of Pain.”

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Repeated evaluations by the same person, if possible, are most valuable while following a course of therapy.

Resources from Zoetis include detailed instruction in the diagnosis and assessment of osteoarthritis pain along with graphics, animations, and video clips. NewMetrica produced and provided the widely used Glasgow and Short Form Glasgow Composite Pain Scale. Their partner organization, VetMetrica, provides vital resources for training and implementation. Together, they have added the Health-Related Quality of Life (HRQL) scale. Their HRQL instrument adopts a more holistic approach, assessing emotional and physical wellbeing. The computer-based scoring algorithm generates a relatively nonbiased decision.

Assessing Chronic Pain

The following outlines several pain scales and examination techniques that practitioners can utilize to assess maladaptive pain in animals. Many of these assessment scales are available online; see Recommended Resources for more information.

Lameness Examination:

Lameness examination at its best is an advanced skill, often best developed by experts in orthopedics and rehabilitation. All clinicians should recognize the most common clinical signs of lameness. Those most familiar with gait analysis can best recognize more subtle but meaningful changes in locomotion. All clinicians can and should appreciate more gross alterations. These include reduced speed, abnormal gait, non-weight bearing, reluctance to move, walking on toes or hocks, dragging a leg, lack of coordination, hopping or lunging gait, difficulty in ambulation, failure to climb, excessive or awkward movements, running, escaping, limited movement, and hiding.

Unidimensional Pain Scales:

An evaluation of global behavioral changes may and should be based on recognition of species-specific collections or suites of behaviors indicative of pain, as listed above. The Numeric Rating Scale and the Visual Analog Scale are typically used as nonvalidated unidimensional assessments. By definition, there is no attempt to ascribe a range of points and then derive a composite score. There is also no specified threshold for action at which the analgesic treatment or modification action is to be triggered by a specific composite score. Unidimensional scoring systems are more subject to bias and variability across evaluators, with the influence of evaluator age, training, and gender recognized as several significant variables.

Descriptor Differential Multidimensional Composite Scales:

Composite pain scales utilizing a more complex contribution of behavioral, physiologic, and occasionally neurochemical markers have been developed, validated, and extensively employed in research on pain and analgesia. The multidimensional composite metrics are based on separate ratings of severity of deviation from normal for a specified collection of behaviors. The individual scores for each behavior of parameter rated are typically summed to calculate a composite score. A specified threshold (number of total points) at which a therapeutic action is triggered is incorporated in these pain scales. Analgesic therapy is indicated once that threshold is crossed.

Specific Behavioral Changes

There are a variety of behavioral changes associated with pain in animals. Vocalization is a dramatic sign because humans are a vocal species, and it is therefore a source of potential bias. But some animals, such as cats, will rarely use vocalization as a sign of pain. In assessing pain, observers should guard against discounting other, more subtle behavioral signs and nonverbal communication.

Sudden or dramatic changes in behavior are significant but may also be over-emphasized in scoring pain behavior. These include vocalizations: crying, barking, hissing; aggression: biting, kicking, pawing, scratching; and non-responsiveness: hiding, motionlessness, silence.

Acute Pain Behaviors in Cats:

  • Poor or lack of grooming
  • Hissing or aggression upon manipulation
  • A tendency to hide the painful part and look normal
  • Dissociation from the environment

Acute Pain Behaviors in Dogs:

  • Hunched or prayer position
  • Glazed facial expression
  • Attention-seeking
  • Whining
  • Licking the painful area

These assessment tools deserve our close consideration. In early versions, some were too cumbersome for practical clinical application. Implementing the best clinical metrology instruments in a busy clinical environment requires practicality and simplicity in their design and the necessary knowledge and training. Some of the standard multidimensional scoring systems, for instance, the Glasgow Composite Measures of Pain Scale (GCMPS) and the University of Melbourne Pain Scale, have been modified and customized as “short form” instruments that more practically meet typical veterinary clinical requirements, while retaining validity. The definitive Glasgow acute pain scale for cats, the Glasgow Composite Measure Pain Scale—Feline (CMPS-F), is a combined composite behavior and facial grimace scale.

Specific Multidimensional Composite Scales:

Facial Grimace Scales: The Wong-Baker Faces Scale or Facial Grimace Scale is a well-known and respected tool for assessment in humans, even in very young children. Recognition of changes from many animal patient’s normal facial appearance is powerful in pain metrics and is validated through appropriate research in many species. However, this does not work for dogs owing to the widely varied facial and skull morphology. In cats, pain is revealed in squinting eyes, whiskers diverted downward, ears back, and the head lowered relative to the thorax. The deviation from normal for each facial indicator is scored in a relative range, and the individual scores are summed to obtain the composite facial grimace score. Scoring systems have been revised to include the facial grimace evaluation as an added component in an interactive, multiparameter, composite behavioral evaluation.

UNESP BOTACATU Acute Postoperative Pain in Cats Scoring in Cats: The BOTACTU pain scoring system for acute pain in cats was developed by Brondani, supported through European and North American research, and validated for postovariohysterectomy (OHE) pain in cats. The original form was time-consuming. The revised short-form of the instrument (UFEPS-SF) incorporates validation for responsiveness, extends coverage of the metric to include orthopedic procedures and a variety of soft tissue surgeries rather than just the initial OHE pain, and streamlines the scale. It remains a highly respected scoring tool for acute feline postoperative pain.

Colorado State Canine and Feline Acute Pain Scales: Although not entirely validated and currently presented for educational use rather than to guide medical decisions, these straightforward graphic instruments for assessing postoperative pain in cats and dogs have gained wide acceptance in many veterinary hospitals. They are convenient, relatively simple to understand and employ, and realistic for many veterinary hospitals.

Canine Brief Pain Inventory (CBPI): This scale, adapted from human metrics of chronic pain, is the evaluation tool used by the US Food and Drug Administration in their evaluation and approval of new medications for the management of osteoarthritis (OA) pain in dogs. It is also practical and proven in clinical situations as a validated composite instrument for the recognition of OA pain, grading the severity of pain, and assessing response to treatment. The CBPI includes three categories for multidimensional evaluation: severity of pain, interference with activities, and quality of life.

Feline Musculoskeletal Pain Index: This is a client-directed questionnaire developed for owner assessment of the severity and impact of musculoskeletal pain in cats. It is available for download (see link below) from North Carolina State University. Further validation and streamlining of the instrument are under development.

Recommended Resources

The ready availability of training modules supporting specific scoring instruments for both acute and chronic pain increases their practicality and improves their uniformity in application. Fortunately, we have many such resources available for training about and implementation of several of the best pain scales. These resources help care teams select the best clinical metrology instruments to meet their needs. The many resources available through these sites also provide information to share with clients so that together we will make valid and useful assessments. 

Short Form GCMPS: www.isvra.org/PDF/SF-GCPS%20eng%20owner.pdf

UMPS: researchgate.net/figure/University-ofMelbourne-pain-scale- UMPS_tbl1_271445502

NewMetrica VetMetrica: newmetrica.com acute-pain-measurement

Feline Grimace Scale: felinegrimacescale.com

Zoetis resources on chronic OA pain in dogs and cats: www.TheNewScienceOfOAPain.com

FMPI: cvm.ncsu.edu/research/labs/clinical-sciences/comparative-pain-research/labs-comparativepain-researchclinical-metrologyinstruments-subjectivenighttime-restlessnessevaluation-snore

CBPI: vet.upenn.edu/research/clinical-trials-vcic/our-services/pennchart/cbpi-tool

CMPS-Feline: bvajournals.onlinelibrary.wiley.com/doi/abs/10.1136/vr.104208; wsava.org/wp-content/uploads/2020/01/Feline-CMPS-SF.pdf

UFEPS-SF: peerj.com/articles/11225/

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Ralph Harvey, DVM, MS, DACVAA, is chair of the Veterinary Advisory Board for the BioTraceIT Corporation, with a focus on the objective assessment of pain. He retired from the faculty of the University of Tennessee College of Veterinary Medicine in 2018, where he taught anesthesia, pain management, and related topics for 33 years.

 

Photo credits: AJ_Watt/E+ via Getty Images; Viktorcvetkovic/E+ via Getty Images

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