Managing Canine Pain

Chapter 1 - Overview of Pain Terminology, Pain Physiology, and Animal Pain "Pain is a more terrible lord of mankind than even death itself." (Albert Schweitzer) (1) "If we keep... animals to give and receive love, as members of our families, we have an insurmountable obligation to not let them suffer. Equally important, it is now definitively known that uncontrolled pain is not only morally problematic when allowed to persist in humans or animals, it is biologically deleterious. Unmitigated pain is a major biologic stressor and affects numerous aspects of physical health, from wound healing to resistance to infectious disease. One remarkable study showed that when pain in rats with cancer was controlled with analgesia versus not controlled, the rats given analgesia had 80% fewer metastatic lesions. The conclusion is inescapable: uncontrolled pain damages health and well-being and can even, if pain is severe enough, engender death." (2)   Introduction Controlling animal pain is an important, achievable therapeutic goal (3) that today's veterinarians are incorporating into their standards of practice. According to the American College of Veterinary Anesthesiologists, "... therapeutic strategies should be aimed at improving an animal's ability to cope with pain, thereby decreasing suffering. Treatment of pain can be considered successful if the degree of pain does not prevent an animal from engaging in relatively normal activities, such as eating, sleeping, ambulating, grooming, and interacting with other members of its species or its care givers." (3)

Did You Know? A "Pain Pathway" Was First Described in the 17th Century. Ancient stone tablets reveal that early civilizations used pressure, heat, water, and sun to treat pain. The Greeks and Romans theorized that the brain and nervous system were integral to the perception of pain. By the 15th and 16th centuries, it was believed that the brain was responsible for sensation and that the spinal cord transmitted sensations to the brain. (1) The first person to describe what is still called a "pain pathway" was René Descartes, a 17th century philosopher, mathematician, and scientist. In his work Description of the Human Body, published in 1664, Descartes proposed that when a person's foot comes in contact with fire, particles of fire travel by means of a "delicate thread" to the brain. He likened it to ringing a bell with a rope. According to The Scientist (4), "The image has endured, perhaps because the shape of a pain signal's pathway from site of stimulus to brain still rings with some truth. . . as Descartes implied, the brain is the ultimate interpreter, able to... modulate the signal and even to create pain without stimulus." Another of Descartes' assertions has not stood the test of time - he believed that "since animals have no capacity for reasoning, they could have no perception of pain, and that their reactions to stimuli that would cause pain were simply the responses of automatons." Descartes' view has drawn many responses, and that of 18th century philosopher Jeremy Bentham is quite direct: "The question is not can they reason? Nor can they talk? But can they suffer?" (5)

  The International Association for the Study of Pain (IASP) defines pain as "an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage." IASP adds that "the inability to communicate verbally does not negate the possibility that an individual is experiencing pain and is in need of appropriate pain-relieving treatment (6)." Does this apply to animals? Though there is "overwhelming scientific evidence" that animals experience or feel pain, "it may not be exactly the same as a human's experience, but there is also no way of knowing if two humans have the same pain experience after an identical injury. Animals live in the moment and feel the pain 'now' and, unlike humans, cannot be comforted by the knowledge that things may be better in a few hours or tomorrow. By accepting that animals feel pain, we can move on to the more important issues of defining, assessing, and learning how to prevent and alleviate their pain." (7) The Companion Animal Pain Management Consortium describes pain as "a complex perception that takes place only at higher levels of the central nervous system (8)." The Pain Pathway Perhaps the simplest way to envision the nociceptive pathway ("pain pathway") is to imagine a chain of three neurons. (Neurons are responsible for receiving, conducting, and transmitting nervous system impulses. A neuron consists of a body, an axon, and dendrites). The first-order neuron originates in the periphery and projects to the spinal cord. The second-order neuron ascends the spinal cord. The third-order neuron projects into the cerebral cortex and other supraspinal structures (9). This system is also called the afferent pain pathway. Nociception is the detection and perception process involved in conveying information about tissue damage to the central nervous system (10). In other words, nociception is the process that leads to the conscious perception of pain (9). The process involves the peripheral and central nervous systems and at least four physiological processes (11).

• Transduction (transfer or conversion) of a painful event that damages normal tissues (noxious stimulus) by specialized nerve endings (nociceptors) into the electrical message to be transmitted in the peripheral nervous system. At this point, an animal may exhibit a withdrawal reflex (e.g., pull back its limb in response). (10, 11)

• Transmission of the message to the cerebral cortex via the spinal cord and relay neurons. (12)

• Modulation of the message as it ascends via the relay neurons. During modulation, certain areas of the brain are stimulated to activate pathways that inhibit the painful stimuli (11).

• Perception or integration of transduction, transmission, and modulation with the individual's own physiology, which results in the experience of pain (12).

An intriguing phenomenon is associated with this process. The pain pathway actually changes over time, altering the body's way of responding to subsequent input. This is called "sensitization." There are two types: peripheral sensitization and central hypersensitization or "wind-up." (11)

• Peripheral sensitization: An event that produces pain can also produce inflammation. The body responds by releasing certain substances, called chemical mediators, at the site of the injury. These mediators can be released by nociceptors, the damaged cells themselves, or inflammatory cells that infiltrate the site of the injury. This process sensitizes the nociceptors in such a way that low-intensity signals that don't normally cause pain become perceived as painful, increasing the response to the noxious stimuli (11).

• Central hypersensitization (wind-up): Events such as surgery or trauma can produce repetitive noxious stimulation that affects certain neurons in the spinal cord. As long as the stimulus is present, the activity of these neurons is up-regulated (continues to increase), which produces a decrease in the response threshold and an increase in responsiveness once the threshold is reached. In other words, the signal transmission to the brain increases, and so does the perception of pain. Pain can occur even after the original noxious stimulation ceases. As wind-up continues, the pain it produces becomes harder to manage (11, 12, 13).

Did You Know? The central nervous system consists of the brain and spinal cord, while the peripheral nervous system is made up of the somatic and autonomic nervous systems.

• The somatic nervous system consists of peripheral nerve fibers that send sensory information to the central nervous system, as well as motor nerve fibers that project to skeletal muscle. The somatic nervous system may also be called the "voluntary" nervous system.

• The autonomic nervous system (also known as the "involuntary" nervous system) controls smooth muscle of the viscera (internal organs) and glands. The autonomic nervous system is divided into the sympathetic nervous system and parasympathetic nervous system. The autonomic nervous system can be thought of as an "involuntary" system that sends signals to cardiac muscle, smooth muscle, and certain glands. Sympathetic innervation causes vasoconstriction, which is narrowing of blood vessels, in response to anxiety, fear, or dehydration. The parasympathetic system is responsible for reducing heart rate and blood pressure, and facilitating digestion and absorption of nutrients, and therefore the excretion of waste products.

Types of Pain

Pain can be described in terms of whether it is protective (physiologic or nociceptive) pain or pain that actually causes damage to tissue (pathologic or clinical pain), and in terms of duration and cause (acute and chronic pain).

• Physiologic or nociceptive pain: localized, transient pain that activates high-threshold sensory nerve fibers, producing responses to protect the animal from tissue injury. This type of pain is nicknamed "ouch pain" and occurs, for example, when a person briefly touches a hot burner on a stove (14).

• Pathologic, clinical or neuropathic pain: results from intense or prolonged noxious stimuli that cause tissue damage and abnormal sensitivity. Traumatic injury and surgery can produce pathologic pain. Clinical damage results from inflammation or central or peripheral nerve injury (10, 14).

• Acute pain: a type of physiologic pain. Acute pain can be incapacitating, moderate to severe pain. Its duration is related to the severity and extent of a given injury. Generally, acute pain resolves when the underlying injury has healed (3, 8, 10, 12). A detailed discussion of acute pain is beyond the scope of this course.

Chronic Pain

Chronic pain is prolonged, continuous or intermittent, (10) pathologic pain that results from an inflammatory or neuropathic process (15). This type of pain typically occurs for more than three to six months, but can last for years (10). Chronic pain is maladaptive. It serves no useful function and is associated with disturbance of physiology, potentiation of other diseases such as cancer, worsening of osteoarthritis, decreased activity, behavior changes such as aggression, depression, and anxiety, and adverse alteration of the human-animal bond (16). It can involve central hypersensitization (wind-up - described above) (8), and is harder to treat than acute pain. Chronic pain can continue after signs of tissue injury are no longer present (9). When chronic pain builds slowly, an animal may learn to tolerate and live with it (17). In instances of chronic pain, stimuli are processed abnormally on a continuing basis, and pain can begin to emanate from nervous tissue as well as from the initial injury (9). It is important to note that chronic pain in companion animals may be a result of underlying conditions such as osteoarthritis, inflammatory disorders (e.g. otitis media), orthopedic problems (e.g. cervical intervertebral disk disease), soft tissue injury (e.g., degloving injuries), nervous tissue injury (e.g., phantom limb pain), dental problems, and tumors, which are themselves chronic (5, 9). In these instances, the goal is treating the cause whenever possible as well as relieving the pain (5). It is also important to be aware that animals with the conditions listed above may or may not develop chronic pain (i.e., altered nervous system processing) (9). See Chapter 4 for information on assessing, treating, and managing chronic pain, particularly in dogs.

Sidebar: Possible Mechanisms Involved in the Development of Chronic Pain Although the precise way in which chronic pain develops in individual animals can be unclear, companion animal pain authorities Drs. William Tranquilli, Kurt Grimm, and Leigh Lamont offer several potential mechanisms (9):

• Sensitization of nociceptors.

• Spread of excitation from damaged neurons to adjacent neurons that normally subserve mild sensations such as non-noxious warmth or pressure.

• Expansion of the peripheral receptive fields of dorsal horn neurons (certain neurons in the spinal cord that are devoted to the central nervous system).

• Increased excitability in populations of neurons within central nociceptive pathways.

• Diminished activity of endogenous (inherent) inhibitory mechanisms, leading to reduced inhibition of excitability within nociceptive pathways.

Sidebar: Chronic Pain versus Intractable Pain (5) Do you know the difference between "chronic pain" and "intractable pain?" "Pain which cannot be controlled by any means is termed 'intractable.' The term 'chronic' usually related to the time course rather than to the nature of the pain, and ease of pain control may also be involved in the definition. However, in veterinary medicine, it is often the attending clinician who [implements] inadequate pain control methods, leading to chronicity rather than truly intractable pain." The takeaway message? The veterinary practice team should not assume that an animal's pain is intractable. Every effort should be made to identify and treat animal pain. See Chapter 4 for information on assessing, treating, and managing chronic pain in dogs.

Signs of Pain The signs are not always easy to see. For example, in a 1996 study at North Carolina State University, researchers filmed dogs postoperatively after spay or neuter procedures. When not in the presence of humans, the dogs appeared uncomfortable and listless. When a person entered the room, the dogs wagged their tails and interacted with the person, essentially "hiding" their pain. (18) Although this study focused on post-surgical pain rather than chronic pain, the lesson is the same - animals may not "tell" us when they are experiencing pain or discomfort. It has also been noted that although domesticated small animals differ from the wild species from which they are descended, cats and dogs remain "genetically programmed" not to show pain - a characteristic exhibited in the wild to protect animals from predators (18). In addition, the way individual animals respond to pain can vary depending on age, health status, species, and breed (3). In its position paper on the treatment of pain in animals, the American College of Veterinary Anesthesiologists (ACVA) notes that individual responses to pain vary, and that it is important to recognize departures from a given animal's normal behavior and appearance. Examples of behaviors indicative of pain in animals include (3):

• Changes in personality or attitude. For example, an animal that is typically docile may become aggressive, or an aggressive animal becomes quiet.

• Abnormal vocalization, particularly on examination of a painful area. Dogs may whine or whimper and cats hiss or growl.

• Licking, biting, scratching, or shaking a painful area. Excessive activity of this type can lead to self-mutilation.

• Changes in coat. Animals in pain may not groom themselves; piloerection ("hair standing on end") may indicate pain.

• Changes in posture or ambulation. Animals in pain may adopt a tucked-up posture.

• Changes in activity level. Animals in pain may pace or show other signs of restlessness, or they may be reluctant to move about.

• Changes in appetite.

• Changes in facial expression.

• Changes in elimination habits.

Other signs can include: hiding, seeking more affection than normal, protecting the injured area to prevent additional injury, and aggressive or defensive reactions to touch. Detecting chronic pain in companion animals can be especially difficult because the related behaviors are typically not as dramatic as behaviors related to acute pain. For example, dogs with osteoarthritis may restrict their activity and show signs of muscle atrophy, discomfort, decreased range of motion and decreased quality of life. Other signs of chronic pain can include reduced appetite, licking the affected area, and lying quietly in an area away from their normal social interaction (19). Diagnosing animal pain involves:

• A physical examination.

• An understanding of unique characteristics related to species, breed, and the individual animal.

• Awareness of the relationship between pain and specific diseases, conditions, and procedures.

• The ability to perceive the signs of discomfort and pain (3).

Consequences of Pain Pain can serve a legitimate biologic function by indicating the potential for tissue damage and stimulating responses that actually contribute to healing (20), but as the ACVA explains, "there are no beneficial effects of unrelieved pain in animals under veterinary care." (3) Untreated pain can actually increase sensitivity to pain (recall the discussion of wind-up, earlier in this chapter) and produce cardiovascular, respiratory, gastrointestinal, fluid/electrolyte, hematological, and renal effects, as well as weight loss, aggression, and self-mutilation behavior (3, 7, 20).

Animal Pain and the Veterinary Community The IASP notes that pain is subjective; that is, pain is a sensation coupled with an unpleasant emotional experience (6). In human medicine, physicians treat pain as a vital sign, along with pulse, temperature, blood pressure, and respiration. The pain pathways that exist in humans are also found in animals, but evaluating animal pain is more difficult. Historically, veterinarians (14, 17, 21, 22):

• Did not have adequate tools for dealing with animal pain.

• Believed that animals did not feel pain.

• Assumed that animals manifesting fairly normal behavior were not experiencing pain.

• Were not well versed in available treatment strategies.

• Were concerned about the cost to clients, and/or,

• Felt that pain was important in keeping animals inactive during the healing process.

In addition, veterinary school curricula did not focus on pain, a topic that "now merits lengthy lectures at veterinary schools, detailed discussions in each veterinary journal, and continuing education seminars devoted exclusively to this issue." (23) During recent years, a number of factors have brought animal pain into the spotlight. According to Dr. William Tranquilli "there are two major reasons that attitudes are changing in veterinary medicine. One is that people are now relatively pain free after surgery, so they expect this kind of care for their pets. Second, advances in oncology and geriatric medicine have forced us to pay attention to chronic pain. We need to meet or exceed the public's expectations for improved perioperative and chronic pain management." (24) Other factors include:

• Advances in the understanding of pain.

• Availability of improved pain therapeutics.

• Improvements in the way pain is assessed.

• An increasing focus on the ethical responsibility to relieve animal suffering.

Pain management "appears poised to become one of veterinary medicine's defining issues in the early part of the 21st century." (25) Since it can be difficult to assess animal pain, some veterinarians now treat patients for pain in instances in which it is assumed an animal is experiencing pain (17). Others may not yet be providing adequate treatment for pain. These veterinarians may be putting themselves at risk, since a veterinarian's failure to treat pain can result in legal action by clients. (26) See Chapter 2 for information on the role of the veterinary practice team in pain management and strategies for managing chronic pain, and Chapter 4 for an overview of managing chronic pain, particularly in dogs.

Chapter Hightlights

• Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage.

• The inability to verbalize does not mean pain is not being experienced.

• There is scientific evidence that animals can experience or feel pain.

• Detecting and perceiving pain involves the peripheral and central nervous systems.

• Pain pathways can change over time in such a way that the pain threshold decreases.

• There are several ways to categorize pain:

  • Pain can be protective (physiologic) or damaging to tissue (pathologic).

  • Pain can be acute (short duration) or chronic (prolonged, harder to treat than acute pain).

• Historically, it has been difficult for veterinarians to assess animal pain.

• There is significant scientific evidence that animals experience pain.

• Advances in the understanding of pain, availability of new therapeutics, improvements in pain assessment, an increasing focus on the ethical responsibility to relieve animal suffering, and a growing expectation on the part of pet owners that their animals will not suffer pain have brought animal pain into the spotlight.

• Animals express pain via changes in behavior, including deterioration of housetraining, crankiness, lethargy, hiding when they do not normally hide, seeking more affection than normal, hunching up, protecting the injured area to prevent additional injury, stiffness, reluctance to move, abnormal vocalization, aggressive or defensive reactions to touch, and altered facial expressions or appearance.

• Diagnosing animal pain involves a physical exam; an understanding of breed and individual characteristics; awareness of the relationship between pain and specific diseases, conditions, and procedures; and the ability to perceive the signs of discomfort and pain.

• Pain can actually be beneficial, indicating the possibility of tissue damage and stimulating responses that promote healing, but untreated pain can produce, exacerbate, and/or potentiate a number of serious health problems.

Chapter 2 - Pain Management and the Veterinary Practice   "When we say 'pain management,' it's not about giving a drug at one point and then saying 'OK, I gave drug, I did my job. It's management. In other words, you don't really know [how much the patient is suffering], so you start to treat it, see how it responds, and ask 'Do I need to give him more, or can I just leave him alone?' It's an art, it becomes interactive." (1) "In a nutshell, pain management can be a win-win-win situation for the veterinary practice employing an aggressive program. Morale and hospital atmosphere are improved as the staff gains confidence and personal fulfillment from providing care that is more humane to patients. Secondly, client satisfaction is enhanced and loyalty to the practice is increased which, in time, lead to increased profitability. Lastly, and most importantly, the overall quality of patient care is improved because pain management is basically good medicine."(2) The Ethical and Philosophical Framework for Treating Animal Pain Examples from veterinary literature acknowledge the need for and role of pain control:

• "Why is it important to treat pain? The most obvious answer to this is that pain causes suffering, and we have an obligation to treat it." (3)

• "Society has become increasingly concerned about animal welfare. Central to the new ethic is the realization that uncontrolled pain and suffering probably represent the greatest harm we can visit upon animals, and thus control of pain and suffering in all areas of animal use is a major moral imperative." (4)

• "During the last decade, medical professionals worldwide have recognized the importance of pain management as an essential component to the delivery of quality patient care. It is now universally accepted that better pain management is better medicine. This awareness has not gone unnoticed by the veterinary medical community . . . Increasingly, the practitioners' success is being measured, in the eyes of the public and pet owners, by their efforts to manage acute pain associated with routine elective and advanced surgical procedures. Perhaps even more importantly, veterinarians are now evaluated, more than ever before, on their ability to effectively communicate and deliver compassionate care as they treat a variety of senior and geriatric diseases that are often characterized by chronic pain and suffering." (2)

• Because animals with naturally occurring disease such as OA and cancer are living longer and undergoing long-term treatment and, in some cases, invasive procedures, it is "important to identify and alleviate chronic pain in these patients. Treating chronic pain may be approached systematically, in conjunction with the owner, to alleviate the animal's suffering and improve its quality of life." (5)

• "Position statements also reflect the current state of pain management... The American College of Veterinary Anesthesiologists' (ACVA) position paper on treatment of pain in animals states that the prevention and alleviation of pain in animals is a central, guiding principle of practice . . . the American Veterinary Medical Association (AVMA) adopted a position statement acknowledging that animal pain and suffering are clinically important conditions that adversely affect an animal's quality of life, and methods to prevent and control pain must be tailored to the animal." (6)

• The American Animal Hospital Association (AAHA) has also adopted a position on the issue of animal pain. Since 1993, AAHA has recommended that veterinarians routinely consider administering appropriate analgesics to minimize pain in their patients. The association has also included pain management standards in their voluntary veterinary hospital accreditation program. In April 2005, AAHA released a Pain Management brochure for pet owners, which includes information about the causes and treatment of pain, the importance of pain control, the signs of pain, and animal pain Frequently Asked Questions (7).

Pain Control Can Add Value to the Practice Making and implementing a decision to focus on pain management can benefit clients, patients, veterinary practice team members, and the practice itself (8, 9). Pet owners know what pain feels like and don't want their pets to experience it. Since clients may not be aware that it is not necessarily easy to detect pain in animals, client education is a must - especially because pain can produce serious consequences (9). Practices that incorporate pain management as a standard and "communicate the costs to clients... usually have no problem with acceptance of additional charges," (9) and, in fact, "clients are generally relieved and thankful that their pet is in caring hands that are committed to pain management as a priority in overall patient care. Practitioners find that these same pet owners often become the most loyal and devoted clients." (2) Focusing on pain management as a standard of practice also conveys a message to members of the veterinary practice team. As Dr. James Gaynor, a leader in companion animal pain management, explains: "If staff members are comfortable with a practice's approach to pain management, they are likely happier and should perform their tasks better. If one of their duties is invoicing clients, for example, charges will be recorded more accurately. This increases income merely because all services rendered are charged for." (9) Members of the veterinary practice team are well-positioned to contribute to pain management in a variety of ways. For example (8):

• The receptionist can learn to recognize signs of pain that require immediate attention when an animal arrives at the practice.

• Members of the team who answer the telephone can ask a pre-specified list of pain-related questions that can help determine whether an immediate appointment should be made.

• Veterinary technicians trained in the signs of animal pain can spot signs of discomfort in animals that are visiting the clinic for non-pain-related reasons. Remember that chronic pain can build slowly enough that clients may not notice changes in their pets.

• Veterinary technicians can teach clients to better recognize and manage pain and serve as a resource for clients with questions about pain management.

• Groomers can be in an excellent position to recognize pain or discomfort because "groomers notice things under all those mats that most owners are not even aware of until the fur comes off. [The groomer] will note several symptoms in pets that show they are experiencing pain, including limping, head shaking, scratching, whining, biting, yelping, scooting, the bad breath of dental disease, goopy eyes, irritated skin, parasites, and foul odors. By looking for these signs of pain, a groomer can identify ear infections, painful limbs or toes, dental disease, hot spots, pyodermas, anal gland abscesses and dry eyes."

Dealing with pain is also an opportunity for veterinarians to reinforce their role as the "recognized health care providers for animals." One author contends that "If veterinary clients are drawn to alternative unproven therapies that may be fueled by compassion but do not work to control pain, the animal may be cheated of a proven modality of pain control, creating an intolerable moral situation for the animal owner and loss of credibility for veterinarians because clients may not be able to judge when pain is (or is not) alleviated. If veterinarians will not manage pain, they also risk a grave loss of credibility among the public, who may then seek to remove the special status of scientifically based veterinary medicine and open animal medicine to the forces of the free market, at an incalculable cost in animal suffering." (4) Integrating Pain Control The first step in developing and implementing a pain-management program is internal education. Veterinarians and members of the veterinary practice team need to develop a working understanding of pain physiology, pathophysiology, terminology, assessment, and management strategies. Pain is the subject of easily accessible resources such as journal articles, seminars, presentations at meetings, and continuing education courses such as this one (2). There are four basic aspects of a pain management program (10):

• Ensuring a strong practice commitment to minimizing pain.

• Adopting a team approach involving veterinarians, technicians, and staff.

• Providing pain management education for all practice personnel and owners.

• Encouraging continuous program assessment and improvement.

Surveys on Pain Management Offer Insights into How Veterinarians Think about Animal Pain In a 2001 AVMA Animal Welfare Forum presentation, Dr. Peter Hellyer of The Colorado State University (CSU) College of Veterinary Medicine and Biomedical Sciences cited several surveys on pain management and the veterinary profession. Although the surveys include information on treating acute pain, the results are instructive nonetheless (6).

• A CSU survey showed that veterinary students, clinical faculty, and staff placed a high importance on pain in animals, and most believed that animals experience pain much the same as people do. The paradox of that survey . . . was that their views on the circumstances that would prompt therapy varied widely, and thus, pain management was not uniform at the teaching hospital.

• In a... survey of British veterinarians, 30% believed "a degree of pain is required to stop the animal being too active post surgery." Yet, most small animals tend to sleep following surgery . . . so that attitude is inconsistent with good medicine. Paradoxically, 95% of those surveyed believed that animals do benefit from perioperative analgesic therapy. Many of the British veterinarians considered treating surgical pain with nonsteroidal anti-inflammatory drugs or opioids, but few administered combinations of different classes of drugs,... the cornerstone of current philosophies of effective pain management.

• A survey of Canadian veterinarians indicated that just under half used analgesics in their patients, and they tended to use them in all postsurgical patients or not at all.

• The British and Canadian surveys revealed that more priority was placed on pain by:

  • Female veterinarians,

  • Veterinarians who treated dogs and cats more than 75% of the time and worked with a veterinary technician,

  • Veterinarians who had attended Continuing Education within the past 12 months.

A 1999 survey conducted among French veterinarians assessed their attitudes toward pain and pain management (11).

• 88.3% of respondents based their evaluation of canine pain on the animal's attitude. Other factors included interaction with the owner, response to palpation of the painful area, and inappetance.

• While only 14.3% felt they had "inadequate knowledge" of pain recognition, 47% judged methods of measuring and controlling pain in dogs to be inadequate.

• Respondents cited difficulties in recognizing pain (58.3%), lack of knowledge regarding use of analgesics (41.7%), and fear of drug side effects (30%) as reasons for instances in which adequate analgesia is not provided.

• Nonsurgical conditions for which pain treatment was considered justified were: osteoarthritis (97.8%), trauma (97.3%), and bone neoplasia (93.4%).

• Female veterinarians were more likely than their male counterparts to evaluate pain and provide analgesics.

• The Owner's Role in Managing Chronic Pain While it is true that the signs of chronic pain can develop slowly and therefore go unnoticed by pet owners, your clients can be the first line of defense against untreated chronic pain. The client is in a position to monitor changes in his or her dog's activity level, mood, and appetite - indirect indicators of pain and pain relief (2). The education provided by your veterinary practice team can make the difference between clients who become part of the pain management team and those who allow their pets to experience pain needlessly. Pain management materials are available for the veterinary practice team to use to help teach clients about animal pain and pain management. For example, earlier in 2005, the American Animal Hospital Association (AAHA) published a simple brochure for pet owners, explaining the basics. Go to www.aahanet.org for information on how to purchase. The International Veterinary Academy of Pain Management (www.cvmbs.colostate.edu/ivapm/) has a video entitled Is Your Pet in Pain? available online for clients, as well as a number of resources for veterinary practice teams. See the sidebar What is the IVAPM? One of the most important messages for clients whose animals may be experiencing chronic pain is that there may be no "recipe" for management. More than one modality may be required, and in fact an individualized, multimodal approach may have to be developed and implemented (10). A discussion of multi-modal pain management is beyond the scope of this course. Owners also need to be aware of the placebo effect (10) and biases related to their own expectations of pain relief (10). Once a pain-management strategy is in place, a simple chart such as the one shown in Figure 1, can help both the client and the veterinary practice team by providing a structured, consistent means to assess pain in the out-patient. Figure 1. Adaptation of the Oxford pain chart for assessment of chronic pain in pets (10)

  		Mon	Tue	Wed	Thur	Fri	Sat	Sun
  Pain Intensity: How bad was your pet's pain today?	Severe
  	Moderate
  	Mild
  	None
  Pain Relief: How much pain relief has the medication given your pet today?	Severe
  	Moderate
  	Mild
  	None
  Side Effects: Has the treatment upset your pet in any way today?
  How effective was the treatment this week? (Circle one choice).		Poor   Fair   Good   Very Good   Excellent

• Click here for a printable version of the Oxford Pain Chart

Sidebar - What is the IVAPM? (12)

The International Veterinary Academy of Pain Management (IVAPM) was founded in 2003 to promote, enhance, and advance pain management in animals. IVAPM "is a multi-disciplinary organization that seeks to promote the acquisition and dissemination of knowledge related to the biology and clinical treatment of pain in animals... The Academy seeks to: provide forums for communication among all interested parties of knowledge concerning the biology and treatment of animal pain, provide continuing education in the area of pain recognition and treatment, and establish a process whereby veterinarians with a special interest in the area of animal pain management can meet a set of prescribed objectives that will ultimately lead to certification as a specialist in the management of animal pain. Finally, the Academy seeks to promote humane, scientific investigation into the biology of animal pain and the assessment of the efficacy of defined treatment modalities."

Chapter 3 - Overview of Conditions Associated with Chronic Pain in Dogs   In reality, the greatest pain-associated welfare issue for dogs... lies in unrecognized, untreated pain resulting from chronic conditions." (1) Leading Causes of Chronic Pain The two leading causes of chronic pain in dogs are osteoarthritis and cancer (2). Other causes include, but are not limited to: central neuropathic pain, pain related to otitis media, and dental pain. Pain management does not take the place of thorough diagnostic evaluation that has the potential to uncover an underlying condition that can be treated (3). Every effort should be made to determine and, whenever possible, treat the cause.

Did You Know? Arthritis Is Nothing New Fossils indicate that as far back as the Mesozoic era - 200 million years ago - reptiles had arthritis. (4)

Osteoarthritis

The term "arthritis" is derived from "arthr(o)," meaning joint, and "itis," meaning inflammation (4). Osteoarthritis (OA), a degenerative form of arthritis, is the most prevalent kind of canine arthritis (5). Though OA is acknowledged as the #1 cause of chronic pain in dogs, its occurrence may be underestimated nonetheless (6). OA is typically a slowly progressing, low-grade (7) disease involving synovial joints. Synovial joints allow flexibility and enable a wide range of motion. They are the most common type of joint and include the hip, knee (stifle), shoulder, and elbow joints. Synovial joints are made up of the joint cavity, articular cartilage, synovial fluid, various ligaments, and the joint capsule with its synovial membrane (8). The synovial membrane is a thin lining that supplies and maintains the viscous synovial fluid responsible for reducing friction as the joints move. OA can be primary or secondary (4):

• Primary OA arises as a result of aging or from defects in the structure and biosynthesis of articular cartilage and is rare in veterinary medicine.

• Secondary OA is considered the most common form of canine OA (9) and can be related to a number of factors, including:

  • Trauma (fractures, ligament injuries).

  • Inflammation (infection, immune-mediated diseases).

  • Developmental abnormalities (osteochondrosis, hip dysplasia, elbow dysplasia).

  • Metabolic, hormonal, neuropathic, and cancer-related disturbances.

  • Obesity - note that although the veterinary community is divided on the potential cause-and-effect relationship between obesity and OA, "obesity is strongly associated with the development of osteoarthritis in people and likely contributes to the progression of OA in dogs." (10).

In animals with osteoarthritis, the protective layer of cartilage at the ends of the bones within synovial joints, called articular or hyaline cartilage, is worn away, which leaves the ends of the bones exposed. See The Mechanics of Osteoarthritis in the next section of this chapter. Some breeds can be characterized by a tendency toward defective cartilage or defects in how the joints fit together. OA can become evident as these dogs age (5).

Sidebar: Canine Osteoarthritis: Prevalence and Breed Disposition It is estimated that osteoarthritis affects 1 in 5 adult dogs over the age of 1 year (11), but OA can affect dogs of any age (12):

Age Group		% of Dogs with OA, by Age
< 5 years		5%
5 - 7 years		14%
8 - 10 years		27%
11 - 13 years		35%
> 14 years		19%

Although approximately half of dogs with OA weigh at least 22 kg/48.4 lb, OA may occur in very small dogs as well (12). In the US, as many as 55% of dogs with OA are untreated (13). Mixed-breed dogs and dogs of any breed, size, weight, and age can show signs of osteoarthritis. While some larger purebred breeds, including Labradors, German Shepherds, Rottweilers, Great Danes, Golden Retrievers, and St. Bernards (14), seem to be particularly susceptible to secondary OA due to canine hip dysplasia (CHD), CHD does occur in small and toy breeds (15).