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Veterinarian Technician September 2007 (Vol 28, No 9) Focus: Physical Rehabilitation

Pain Management in Surgical Patients

by Marcy Stellfox, BA, Jim Richardson, DVM, DABVP

    CETEST This course is approved for 0.5 CE credits

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    Key Points

    • All mammals process pain in the same way.
    • Pain management protocols must be tailored according to each patient's needs.
    • Untreated pain may have detrimental side effects.

    Click here for Glossary.

    Research into pain perception in human neonates and animals has led to re­vised approaches to pain management in patients that cannot express pain in words. Use of multiple analgesic agents to block the transmission and perception of pain during surgical procedures can not only increase patient comfort but also prevent the negative consequences of untreated pain (see Pain Management Agents Commonly Used in Surgical Patients). As patient advocates, veterinary technicians should be able to communicate the importance of effective pain management to clients. (See Analgesic Adjuvants .)

    Until the late 1980s, it was thought that human newborns did not feel pain as acutely as did older children because their nociceptive (pain-sensing) systems had not fully developed. However, more recent studies have changed the way many medical professionals view the perception of pain in human newborns. A study published in the New England Journal of Medicine in 1987 reported that "human newborns do have the anatomical and functional components required for the perception of painful stimuli."1 Other more recent studies have confirmed these results.2,3 In fact, further evidence suggests that newborns actually have a heightened sense of pain because they lack a fully developed nervous system.2-4

    As the results of studies of pain in human neonates became more widely known, many laypeople and medical professionals demanded better pain management for neonates, and as pain management became the accepted standard of care for newborns, physicians discovered that survival rates decidedly increased. Based on the combination of new clinical experience and scientific research, in 1998, the Veterans Health Administration launched the National Pain Management Strategy, which called for pain to be recognized as the fifth vital sign5,6 after heart rate, blood pressure, temperature, and respiration.

    Similar to human neonates, puppies have been found to respond to a toe pinch at birth and are thought to have a lower tolerance to pain than older animals.7,8 Puppies can perceive pain, but their ability to withdraw and escape from it does not develop until a few weeks after birth.7 Increased knowledge and experience in human and animal medicine has led to new thoughts about pain management in animals. As primary caregivers, veterinary technicians have a unique responsibility to animals because technicians are the patient's advocate. They are also usually the first members of the veterinary team to observe and respond to an animal's pain and, therefore, should have a clear understanding of how to best recognize, assess, and manage pain.

    The keys to providing excellent pain management in the practice are as follows:

    • Know and recognize the clinical signs of pain , and remember that pain has negative effects on the body.
    • Make pain assessment a routine part of assessing the vital signs of every patient. The patient's pain level should be periodically reassessed and recorded in the medical record.
    • Study and understand the anatomy and physiology of the pain pathway, including how pain signals are generated and travel through the body. Be able to apply this knowledge and determine ways to effectively treat pain.
    • Practice preemptive and multimodal pain management. Learn the pharmacology of the most common drugs, understand which drugs work synergistically, and know contraindications for drug classes. Also, know the different stages along the pain pathway and which drugs interact with the body's systems to suppress or eliminate pain signals and perception — which occurs only in the brain — at each stage.

    Recognizing Signs of Pain

    For years, animal care providers have tried to understand how animals experience pain. This process is difficult because animals cannot express their feelings in words and objective assessment of pain in animals has limitations. In fact, a widely standardized method for assessing pain currently does not exist, although various pain scales have been developed.

    Animals have natural survival instincts, and in the wild, those that are sick or weak are most in danger of being preyed upon. Therefore, animals instinctively hide pain.9,10 It is important to be able to recognize the signs of pain and to interpret them properly. Some signs are more obvious than others. Recognizing the more subtle signs of pain as well as the obvious signs is vital to treating pain successfully.

    Vocalization and lameness may be the most readily observable signs of pain in animals; however, changes in posture and behavior also may indicate pain. Signs that are not obvious to the owner may include tachycardia, increased or shallow respiration, increased body temperature, a feeling of warmth or heat at the affected site, lack of appetite, or changes in blood pressure.

    Laboratory results may show other changes that are not visible when animals are in pain (e.g., neutrophilia, polycythemia, elevated cortisol levels [resulting in leukocytosis], elevated catecholamine levels, hyperglycemia). These results can also be observed in animals under stress and are not necessarily specific to an animal in pain.11

    It is necessary for each staff member to be aware of the detrimental effects that pain can have on an animal. For purposes of client education, it is important that the client receives the same information about the importance of treating pain from each member of the hospital staff, regardless of his or her position in the clinic.

    Reasons to Assess and Manage Pain

    Untreated pain can have many detrimental effects on body systems. Several studies11-13 have reported the negative physiologic, metabolic, and immunologic effects of pain, including the following:

    • Ventilation-perfusion abnormalities
    • Increased metabolic demand
    • Increased tissue catabolism
    • Impaired immune function
    • Increased risk of sepsis
    • Poor or delayed wound healing
    • Cardiovascular stress
    • Decreased gastrointestinal motility
    • Imbalance in body fluids
    • Prolonged hospitalization
    • Increased mortality

    Central nervous system changes can include hypersensitivity to low-intensity painful stimuli (hyperalgesia) and nonpainful stimuli, resulting in excessive perception of pain (allodynia).

    As patient advocates, the members of the veterinary team must be knowledgeable about these negative effects and endeavor to avoid them by including pain management as a routine part of patient care. Recently, the American Animal Hospital Association (AAHA) developed standards for pain management that member hospitals must follow to maintain AAHA certification. A copy of these standards can be viewed at the AAHA Web site (www.aahanet.org). AAHA recommends assessing pain in every patient that enters the hospital, regardless of the reason for the visit, and using a pain scale to rate the pain. This pain rating is recorded in the patient's file and becomes part of the permanent record.

    Charting the pain level can also be useful in determining whether the current pain protocol is effective for a particular patient. Therefore, it is essential that the veterinary technician regularly assesses the patient's pain level. Various pain scales can be used to assess, rate, and monitor pain. These scales include the visual analog scale, which ranks the level of pain along a line on which one end represents no pain and the opposite end represents the worst possible pain. The numerical rating scale uses numbers on a scale from 0 to 5 or 0 to 10 — 0 represents no pain, and 5 or 10 represents the most severe pain. Finally, the categorical scale divides pain into four categories — none, mild, moderate, or severe. For purposes of uniformity and comparison, it is best to select one scale to use for all patients.

    The Physiology of the Pain Pathway

    To provide excellent pain management, it is first necessary to understand the definitions of the different types of pain, the physiology of the pain pathway, the pharmacology of pain medications, and how medications act to reduce or stop pain signals from traveling through the pain pathway.

    Pain is most simply defined as a feeling of distress, suffering, or agony caused by the stimulation of specialized nerve endings.14 It can be categorized based on anatomic origin:

    • Physiologic pain is caused by stimulation of nociceptors that trigger a response in the A delta and C nerve fibers. This type of pain is a protective mechanism used by the body to "teach" itself to withdraw from a specific noxious stimulus (painful event) causing the tissue damage.13,15
    • Peripheral pain can be visceral or somatic. Visceral pain is thoracic or abdominal and is described as a dull ache or a gnawing or cramping feeling. It is difficult to pinpoint the exact location of visceral pain, which is caused by the stimulation of C nerve fibers only. Somatic pain is localized and is felt in the joints, muscles, skin, or periosteum. It can be described as a stabbing or throbbing feeling and is caused by the stimulation of C nerve fibers and A delta nerve fibers.13,15
    • Neuropathic pain results when the peripheral nerves or spinal cord are damaged or sensitized. The pain is described as burning or intermittent. Neuropathic pain is difficult to treat and often does not respond to traditional pain relievers such as NSAIDs and opioids.15,16
    • Idiopathic pain is not a reaction to a painful event and is not directly linked to a specific origin. This pain is more typical of behavior problems and emotional stress.15

    Because humans and animals have similar anatomic structures and physiologic processes of pain perception,12 it should be assumed that the pain pathway is the same in animals and in humans. It is now a widely held belief that all mammals process pain signals similarly.17 Although animals cannot describe the pain verbally, these similarities should be reason enough to assume that if a surgical or diagnostic procedure causes pain in human patients, it will also cause pain in veterinary patients.12

    The pain pathway begins with the pain receptors, or nociceptors, which are found throughout the skin, peritoneum, pleura, periosteum, subchondral bone, joint capsules, blood vessels, muscles, tendons, fascia, and viscera.15 When a noxious stimulus is experienced, three distinct processes take place15:

    • Transduction — The nociceptors at the site of the painful event change the chemical, thermal, or mechanical energy into electrical impulses.
    • Transmission — The electrical impulses travel through a three-neuron chain: The first-order neurons travel from the site of the painful stimulus to the dorsal horn of the spinal cord; the second-order neurons in the spinal cord send pain signals to the brain (especially the thalamus); and the third-order neurons carry the pain signal into the cerebral cortex.
    • Modulation — Endogenous analgesic systems (opioid, serotonergic, noradrenergic) release naturally occurring analgesics to inhibit the processing of stimuli within the spinal dorsal horn cells. In other words, some analgesic properties naturally reside within the body.

    Perception is not part of the nociception process (there are no nociceptors in the brain) — it is the result of this process. It is within the cerebral cortex that nociception concludes and pain is felt.

    Physiologic Consequences of Inadequate Pain Management

    When pain is inadequately treated, wind-up phenomenon occurs. In this process, repetitive noxious stimulation bombards the spinal cord with pain signals, thereby prolonging the discharge of dorsal horn cells.16 Just as muscles develop with repetitive action, these pain receptors become highly sensitized to pain signals. Dorsal horn neurons that become overly sensitized alter the natural state of the nervous system by leading to the death of certain cells through a condition called excitotoxicity.15,16 Wind-up phenomenon has also been associated with other conditions, such as chronic pain, in which the altered state of the nervous system is unable to normalize.

    Another effect of untreated pain is that the pain receptors become hyperexcited. When this occurs, hyperalgesia can develop. During hyperalgesia, a noxious stimulus that normally is minimally painful (e.g., a needle stick) can become significantly painful because of increased sensitivity at the site of the stimulus (primary hyperalgesia).16 Dorsal horn neurons may become increasingly sensitized, and areas surrounding the site of the actual injury may also transmit pain signals (secondary hyperalgesia).16 If the pain is not treated and the noxious stimulus continues, allodynia can develop. In allodynia, receptors typically reserved for pleasant sensations also become hypersensitive to pain and are, in fact, recruited by the pain receptors. Then they too begin to transmit pain data. In this case, even sensations that are typically pleasant to an animal (such as petting) are perceived as painful events. When allodynia exists, pain becomes extremely difficult to treat because the nervous system no longer reacts normally to analgesic administration. In some instances, it can be almost impossible to relieve the pain.

    Preemptive analgesia can prevent wind-up phenomenon by treating pain before a painful event occurs, thus ensuring that hyperalgesia or allodynia does not develop. For example, a spay patient that has normal preoperative laboratory results and no other contraindications is administered an injectable NSAID before induction of anesthesia. The animal is then given a combination of an opioid and a2 agonist to aid in analgesia and mild sedation to ensure a smooth, stress-free induction. The NSAID inhibits the inflammatory response at the surgical site, the opioid inhibits activity at the dorsal horn and the brain where opioid receptors exist, and the a2 agonist blocks the a2 receptors in the central nervous system.11

    Strategies for Pain Management

    The importance of preemptive analgesia is significant because it lessens the duration and intensity of postoperative pain, decreases the chances of wind-up phenomenon developing, and therefore reduces the risk of a chronic pain state.15 Because the different receptors of the pain pathway are blocked before the introduction of noxious stimuli, the pathway that pain travels on its way to perception is interrupted, and pain is not experienced. As an analogy, imagine that pain receptors are seats in a stadium. All of the seats are filled with home-team fans (analgesics). An opposing-team fan (pain signal) arrives and tries to find a seat. Because the home-team crowd has filled all of the seats, the opposing-team fan has nowhere to sit and therefore is unable to "experience" the game. In the same way, when preemptive analgesia is used, the pain receptors are filled with analgesics that block the pain signals from bombarding the dorsal horn neurons.

    Relieving pain is more difficult than preventing it. Once a painful event is perceived, the pain signals begin bombarding the receptors, and the pain pathway is operating without obstructions. The analgesics now must block the receptors from receiving the signals and stop the bombardment. To continue with the above analogy, the stadium seats are now filled with opposing-team fans, and the game has started. The home-team fan (analgesic) is seeking a seat and must convince an opposing-team fan (pain ­signal) to give up his or her seat.

    Analgesia and Sedation

    Analgesia is the absence of pain sensation,15 and sedation refers to the calming of fear or excitement. It is important to recognize the difference between these two terms and how the drugs that provide these characteristics can be combined to provide synergistic benefits. Analgesia provides pain relief or inhibits pain signals from charging along the pain pathway, thus inhibiting the perception of pain. Sedation, however, prohibits the stress response from activating. The stress response can be stimulated in any circumstance in which an animal experiences fear or anxiety and therefore is not limited solely to events that cause a pain response.11 Stress can trigger the "fight or flight" reaction and can affect the autonomic nervous system by causing the release of catecholamines and corticosteroids, leading to changes in heart rate, blood pressure, and respiratory rate.11 Changes in blood chemistry, such as changes in blood viscosity, clotting times, and platelet aggregation, may also be seen as a result of the stress response.14 Using drugs with analgesic and sedative characteristics simultaneously can inhibit the animal's pain and stress responses.

    Use of Single Agents

    In some instances, the use of a single agent can provide adequate pain relief from a minor painful event or procedure. Local anesthetics can be used alone for procedures such as implanting a microchip, suturing minor wounds, or removing skin tags. NSAIDs may be used alone for procedures such as a routine ear flush as long as the animal is healthy and baseline blood work results indicate they can be used safely. NSAIDs should be avoided in animals receiving therapeutic treatment with corticosteroids because of negative interactions, including gastrointestinal (Gl) issues and renal toxicity.15

    For more complex procedures, higher doses of a single agent may be required to achieve therapeutic benefits. Higher doses put the patient at greater risk for the possible adverse side effects of an individual drug. Therefore, for patients undergoing more invasive, painful procedures, the synergistic effects of multiple therapeutic agents provide better pain control at lower dosage levels, which makes the agents safer to use.10,15

    Multimodal Pain Management

    The next step of effective pain management is the use of multimodal pain management. This technique can be described as use of different drugs with different mechanisms of action (sometimes from several classes) combined with different administration techniques that result in pain control across several body systems.15,18 Although it may seem that this practice would duplicate effects on various stages along the pain pathway, in a well-designed protocol, each drug acts on different pain receptors along the pathway or in the brain in slightly different ways, thereby ensuring that pain is reduced as much as possible at each stage.

    For example, when using a preoperative combination of an a2 agonist (e.g., medetomidine) and an opioid (e.g., morphine), pain is reduced at all stages along the pain pathway. Both classes of drugs stop pain at modulation and perception; however, they act on different pain receptors within these stages. Opioids stop pain during transduction, and a2 agonists stop pain during transmission. An induction agent, such as a 50:50 combination of diazepam and ketamine, can then be used and given to effect. Intraoperatively, a constant-rate infusion (CRI) intravenous drip with ketamine can also be used to enhance the effects of the induction dose. Diazepam inhibits pain at the perception phase, and ketamine inhibits N-methyl-d-aspartate (NMDA) receptors in the dorsal horn,16 helping to prevent central sensitization and wind-up phenomenon during the modulation phase. Thus, pain is inhibited along the pain pathway at all stages (transduction, transmission, modulation), and several pain receptors are also inhibited at those stages.15

    Patients that received effective preoperative and intraoperative analgesics should have less intense postoperative pain, leading to a decreased need for postoperative medication to alleviate pain. Ketamine can also potentiate the effects of postoperative pain medication,15,19 thereby lowering the doses of the drugs needed to relieve postoperative pain.

    Another benefit of using multimodal analgesia is that a lower level of maintenance gas (inhalant) anesthesia can usually be administered because of the synergistic effects of drug combinations. Using less inhalant gas can reduce the risks of potential adverse side effects, such as decreased body temperature, hypotension, and respiratory depression.

    There is no uniform analgesic or anesthetic protocol that is safe for all animals. Therefore, it is important that the drug protocol be tailored to each patient's individual needs after a physical examination has been performed, the blood work analyzed, the patient's medical history obtained, and the planned procedure considered. For example, NSAIDs are not appropriate for patients with renal insufficiency or for patients with a history of GI ulcers or GI bleeding. Similarly, a2 agonists may be inappropriate for patients with cardiac disease. Also, some drugs may provide benefits other than pain relief, such as sedation, or may provide prolonged pain relief when used together with a known analgesic. It is important to remember that these drugs should not be used for the sole purpose of pain relief and do not effectively treat pain unless they are used in combination with other analgesics.

    One criticism of the multimodal analgesia approach is that numerous controlled substances can be involved, which makes record keeping cumbersome. However, the quantities of substances are smaller, providing greater safety against accidental overdose. Using smaller drug doses also minimizes the risk of adverse side effects. In the case of inhalant anesthetics, less gas is needed to maintain the anesthetic plane. In addition to decreasing the negative side effects of inhalant gas, using less gas will allow the patient to return to consciousness more quickly after surgery. Thus, using the multimodal approach is safer for the patient. The safety of the patient outweighs the annoyance of burdensome record keeping.

    Preoperative Administration of Drugs

    A good preoperative combination of drugs is vital to successful pain management because it aids in preventing wind-up phenomenon. Also, animals that have had proper preoperative and induction agents are more likely to move smoothly into the anesthetic plane, which aids in a smooth recovery from anesthesia. Drugs that provide effective analgesia with some sedative properties, such as the preoperative combination described above, should be used. In the previous example, the a2 agonist provides sedation and analgesia; the opioid provides even greater analgesia by blocking the mu receptors.

    Administering an NSAID before surgery can inhibit the inflammatory response that occurs at the surgical site, thereby preventing pain before it begins. NSAIDs are also effective at stopping pain at the modulation phase by inhibiting the spinal cord from processing painful stimuli.12 As mentioned previously, preoperative blood work should be carefully reviewed before NSAIDs are administered to rule out renal disease. It is also important to study the patient's medical history for incidences of blood clotting abnormalities or GI bleeding and to ensure the animal is not receiving other medications to treat renal disease, GI issues, or blood clotting disorders.15 NSAIDs may also interact negatively with corticosteroids by enhancing GI or renal toxicity and may act synergistically with opioids by enhancing their analgesic effects.15 Finally, intravenous fluids should always be used when a preoperative NSAID is administered to enhance renal efficiency.

    Intraoperative Pain Management

    Local anesthesia can be used for patients undergoing declawing, tooth extraction, or tumor removal. When administered via an epidural injection, local anesthetic agents and opiates can also be used for more painful surgical procedures, such as anterior cruciate ligament repairs and amputations. Intraoperative pain medication can also be administered continuously through CRI intravenous drips. It is recommended that a loading dose of the drug to be used in the CRI be given before administering the CRI.15 Careful calculation of the drug concentration to be added to the fluid bag and calculation of the fluid rate are necessary to ensure proper hydration and adequate delivery of the CRI agent.

    Postoperative Pain Management

    Pain must be continuously assessed and managed during the postoperative period because each patient experiences the intensity of painful events differently, shows signs of pain differently, and reacts to therapeutic agents differently.10,11 As a patient recovers from surgery, it sometimes is necessary to administer additional pain medications. Typically, the first 12 to 24 hours after surgery are believed to be the most painful13; however, animals that exhibit signs of pain should continue to be treated until these signs have subsided. Abruptly discontinuing analgesic therapy before pain has subsided can lead to reactivation of the excitatory process of the pain pathway, which may result in the development of wind-up phenomenon and long-lasting detrimental effects associated with untreated pain.

    Postoperative administration of pain medication may include NSAIDs and opioids delivered intravenously, intramuscularly, or subcutaneously.13 A transdermal patch containing fentanyl also may be used. This method of delivery can have a lag time of between 6 and 24 hours, and each animal absorbs the drug at a different rate.15 Absorption rates are also affected by location, thickness of skin, and body temperature.20 Therefore, regular postoperative pain assessment is still important, and animals still exhibiting pain after patch application should be treated using other methods until signs of pain disappear. Finally, to prevent accidental ingestion, the patch should be covered with a bandage and placed in an area that is difficult for the animal to reach. When used properly, this method is very effective at relieving postoperative pain for up to 72 hours.21

    A relatively new development for postoperative pain relief includes using a soaker catheter. This technique involves stitching a multiholed catheter tube into the skin at the wound or incision site, allowing local anesthetics to be delivered in the same way that a "soaker hose" delivers water to a garden.10 Medications such as NSAIDs or low-dose opioids can also be dispensed to the client to provide pain relief at home. It is important to educate the client not only in how to properly administer pain medications at correct dosages but also in how to recognize outward signs of pain in their pet. Clients should be aware that if the procedure causes pain in humans, it also causes pain in their pet. Clients should be advised that abnormal behavior and observed signs of pain could impair proper healing and lead to deterioration of the patient's condition and that additional treatment from their animal care provider may be warranted.

    Appropriate Use of Pain Medication

    Regardless of the animal's outward behavior, pain medication should be administered at an appropriate level for the assumed duration and level of pain according to the procedure performed. The old theory — that it is beneficial to allow an animal to feel some pain to keep it from doing additional harm to itself — is a myth. It has been reported11 that recovery time in animals is longer when they are in pain, and the other detrimental side effects of pain, such as poor wound healing, increased complications, and even increased mortality rates, show that alleviating pain to avoid these compli­cations is the best practice. In addition, it is far easier to prevent pain than to treat it once it is established in a patient. Once wind-up phenomenon develops, and if hyperalgesia or allodynia follow, the altered state of the nervous system may make it more difficult, if not impossible, to treat the pain.14-16,22 In fact, extreme pain occasionally can permanently alter the nervous system, in which the "memory" of pain causes a condition known as chronic neuropathic pain.16,23 Once this condition develops, traditional pain management techniques may be ineffective16,22 because the pain is not caused by actual tissue damage but is caused by an altered state of the nervous system. This is the most important reason why preemptive analgesia is required and why wind-up phenomenon should be prevented.

    Conclusion

    As advancements in pain management techniques and evidence of the detrimental effects of pain become more widely known, clients will expect pain management for their pets and will seek animal hospitals with excellent pain management protocols and well-educated staff. For veterinary technicians and veterinary nurses, one of the most important aspects of care is the relief of pain and suffering. Knowing the signs of pain, how pain is processed in the body, and how it is appropriately managed is necessary to provide excellent care and can lead to healthier and happier lives for patients.

    1. Anand KJ, Hickey PR: Pain and its effects on the human neonate and fetus. N Engl J Med 317(21):1321-1329, 1987.

    2. Holsti L, Grunau RE, Whifield MF, et al: Behavioral responses to pain are heightened after clustered care in preterm infants born between 30 and 32 weeks gestational age. Clin J Pain 22(9):757-764, 2006.

    3. Page GG: Are there long-term consequences of pain in newborn or very young infants? J Perinatal Educ 13(3):10-17, 2004.

    4. Saniski D: Neonatal pain relief protocols in their infancy. NurseWeek 2005. Accessed July 2007 at http://www.nurseweek.com/news/Features/05-02/Clinical_BabyPain.asp.

    5. Department of Veterans Affairs: Pain management. Accessed August 2007 at www1.va.gov/geriatricsshg/docs/PainManagement.pdf.

    6. Phillips DM: JCAHO pain management standards are unveiled. Joint Commission on Accreditation of Healthcare Organizations. JAMA 284 (4):428-429, 2000.

    7. Landsberg G, Hunthausen W, Ackerman LL: Puppy and kitten development, in Rodenhuis J (ed): Handbook of Behavior Problems of the Dog and Cat, ed 2. Philadelphia, WB Saunders, 2003, pp 16-17.

    8. American College of Veterinary Anesthesiologists: Position paper on the treatment of pain in animals. Accessed August 2007 at www.acva.org/professional/Position/pain.htm.

    9. Villalobos A: Cancer pain: Understated shouldn't mean underestimated. Veterinary Practice News. Accessed August 2007 at www.animalnetwork.com/petindustry/vpn/ooweb0207.asp.

    10. Limon L: Boosting the odds of recovery. North Grafton, Massachusetts, Tufts University, Magazine of the Cummings School of Veterinary Medicine 8(2)2-1, 2006.

    11. McCurnin DM, Bassert JM: Pain management, in Schrefer JA (ed): Clinical Textbook for Veterinary Technicians, ed 5. Philadelphia, WB Saunders, 2002, pp 510-525.

    12. Boothe DM, Tranquilli WJ, Radasch RM: Analgesic drug options for targeted patients: Overview of pain and analgesic drugs, in Tranquilli WJ (ed): Practical Pain Management: A Clinical Approach to Everyday Cases. Wilmington, DE, The Gloyd Group, 1999, pp 3-28.

    13. Paddleford RR: Manual of Small Animal Anesthesia, ed 2. Philadelphia, WB Saunders, 1999.

    14. Thurmon JC, Tranquilli WJ, Benson GJ: Lumb & Jones Veterinary Anesthesia, ed 3. Baltimore, Williams & Wilkins, 1996.

    15. Tranquilli WJ, Grimm KA, Lamont LA: Pain Management for the Small Animal Practitioner. Jackson, WY, Teton NewMedia, 2000.

    16. Richeimer S, Macres SM: Understanding neuropathic pain. SpineUniverse 2000. Accessed June 2007 at www.spineuniverse.com/displayarticle.php/article1514.html.

    17. Nolen RS: The problem with pain. Veterinarians are making a thorny issue a priority. Accessed August 2007 at www.avma.org/onlnews/javma/aug01/s080101b.asp.

    18. Short CE, Ko J: Balanced multimodal pain management for diagnostics and surgery. Clinician's Update, August 2006. Accessed August 2007 at www.cliniciansbrief.com/cms/portals/_default/pdfs/supplements/FDCU06%20Opioids%20Aug%20wrefs%20final.pdf.

    19. Menigaux C, Fletcher D, Dupont X, et al: The benefits of intraoperative small-dose ketamine on post-operative pain after anterior cruciate ligament repair. Anesth Analg 90:129-135, 2000.

    20. Gottlieb A: Analgesic options for managing pain in cats and dogs. Vet Tech 23(10):638-645, 656, 2002.

    21 Hofmeister EH, Egger CM: Transdermal patches in small animals. JAAHA 40:468-478, 2004.

    22. Rajagopal MR: Pain: Basic considerations. Ind J Anaesthes 50(5):331-334, 2006.

    23. Office of Public Engagement, University of Illinois, College of Veterinary Medicine: Pain management is now for pets too. Pet Columns 2002. Accessed June 2007 at www.cvm.uiuc.edu/petcolumns/showarticle.cfm?id=349.

    References »

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    CETEST This course is approved for 0.5 CE credits

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