Is Postoperative Pain Management Important in Dogs and Cats?
<<Vet Med 94[3]:254-257 Mar'99 Symposium 24 Refs
James S. Gaynor, DVM, MS, Dipl. ACVA
Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, 80523
- Substantial advances in our understanding of acute pain physiology and therapy in animals and people have occurred in recent years. Despite the availability of numerous pain-relieving techniques and drugs in veterinary medicine, many animals remain untreated after potentially painful events such as surgery and trauma. This article discusses why these animals may be under-treated for pain, as well as the biologic role and physiologic consequences of pain.
Why is pain undertreated? Veterinarians may not administer analgesics to dogs and cats for several reasons. Some veterinarians still think that dogs and cats do not feel pain. Others think that if an animal can walk and eat it must not be in pain. But behavioral changes exhibited after routine surgeries (e.g. ovariohysterectomy) suggest that animals, even those walking and eating, may be in great pain. Some veterinarians do not provide analgesia to their patients because they lack knowledge about available drugs. Another reason veterinarians may not aggressively treat pain is because they have difficulty assessing it. There are no perfect ways to assess pain, but several scoring systems are available to help practitioners do so more objectively. Many people recommend that animal-care providers simply assume that pain occurs in animals under the same circumstances as in people. Finally, the cost of analgesic drugs and the need to charge clients more may inhibit appropriate pain management. The financial aspects of pain management will be discussed next month in Part 2 of this symposium.
Aside from moral and ethical considerations, tremendous evidence suggests that pain and the resulting stress response can have marked, if not catastrophic, physiologic effects. Providing analgesia to people helps blunt the stress-response and the adverse sequelae. Evidence suggests that veterinary patients similarly benefit from analgesia. Pain management should be instituted in all veterinary patients who may experience pain to minimize the likelihood of cardiovascular, pulmonary, fluid and electrolyte, or gastrointestinal problems.
VIN SUMMARY:
This introductory article discusses the biologic and physiologic role of pain.
The treatment of pain in patients is predominantly underused. Since our patients can not tell us if they are in pain, we must observe the patient, make some assumptions, and treat to alleviate the pain.
Biologic role of pain
Pain has a biologic role in survival.
Pain signals actual/impending tissue damage; this may cause animals to attempt to avoid further harm.
Pain immobilizes (or decreases use) of the body (damaged tissue). However, excessive immobilization can cause decreased musculoskeletal and cardiopulmonary function.
Pain results in neurohumoral responses which can aid healing. However, if excessive, this can cause increased morbidity & mortality.
Physiologic consequences of pain
Acute injury stimulates a generalized stress response -- increased ACTH, cortisol, antidiuretic hormone (ADH), catecholamine, aldosterone, renin, angiotensin II, & glucose concentrations, and decreased insulin & testosterone concentrations.
Stress response produces (can be manifested in the immediate postoperative period):
a general catabolic state (muscle protein catabolism & lipolysis, water & sodium retention, and potassium excretion).
a slower rate of healing, if the stress response is prolonged.
changes in the cardiovascular systems
catecholamine, angiotensin II, & ADH lead to cardiovascular changes which include:
vascular resistance due to arteriolar constriction (seen as higher blood pressure)
venous constriction (results in decreased venous capacitance)
cardiac contractility
heart rate
These responses may be initially beneficial, but ultimately result in myocardial oxygen consumption.
Myocardial O2 consumption + ¯ myocardial perfusion = myocardial hypoxia or ischemia (with resultant cardiac dysrhythmias)
changes in the respiratory systems
metabolism and changes in pulmonary vascular tone
impaired respiratory function
This combination results in carbon dioxide production, oxygen consumption, ventilation-perfusion mismatching, & atelectasis, all of which predispose the patient to hypoxemia.
fluid and electrolyte imbalances
aldosterone concentrations lead to sodium retention
catecholamine & cortisol concentrations contribute to potassium wasting
(Fluid retention and decreased urine output are very serious in heart or renal disease patients.)
catecholamine concentrations lead to ¯ bowel motility and ¯ blood flow to viscera. As gastrointestinal edema increases and bowel motility decreases, bacterial overgrowth, bowel ischemia, & bacterial translocation occur.
Summary
Pain and the resulting stress response can have marked-to-catastrophic physiologic effects. Pain should be controlled in order to minimize the cardiovascular, pulmonary, fluid & electrolyte, and gastrointestinal complications.
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vinid = JA013427, date0499
Journal info: ISSN 8750-7943; ID=J035, VM
All rights reserved, copyright, Veterinary Information Network, Inc., 1999