The analgesic triad: Managing patient pain from oral disease
Veterinary patients with chronic oral disease requiring oral surgery benefit tremendously from what I call the analgesic triad: continuous rate infusions (CRIs), physiologically targeted post-operative analgesics and regional nerve blocks. Each component complements the other two, maximizing pre- and post-operative patient comfort and intraoperative safety, and aids the knowledgeable practitioner in safely managing surgical patients with chronic oral pain.
Painful or not?
Veterinary patients with chronic oral disease often do not demonstrate clinical signs attributable to oral pain. This is unfortunate, because patients often suffer for extended periods of time before abnormalities are noticed and addressed. Even more unfortunate is the fact that many pets with chronic oral disease never receive care either because of pet owners' lack of compliance or failure to notice. In my experience, the vast majority of patients do not present for oral pain. Postoperatively, however, the patient whose oral disease is surgically eliminated will demonstrate positive signs consistent with pain resolution. Pet owners consistently and overwhelmingly report behavioral changes consistent with a healthier pet. These include greater appetite, increased activity, playful behavior and a return to oral manipulation of toys or chews.Client education
Awareness of the behavioral changes above is crucial in client education. The majority of patients won't demonstrate pain that pet owners can recognize during an initial client education discussion. Use these first discussions immediately following recognition of the pet's existing disease as an opportunity for education.
CRIs and post-operative analgesics
Wind-up. Patients with chronic oral pain benefit from analgesics that decrease the effect of proalgesic mediators within the modulation center of the brainstem. Glutamate and substance P are two such compounds that act in concert to allow exaggerated pain impulses to reach the higher brain centers resulting in pain perception. CRI use with compounds that alter this effect block the NMDA receptors that allow pain signals to reach perception. Ketamine is commonly used to modulate pain signals within the brainstem by blocking the NMDA receptor. Lidocaine has been shown to act centrally to decrease central sensitization and is used in the CRI regimen in dogs. Doses and calculations can be done with a free spreadsheet available online at http://www.vasg.org/.
Peripheral sensitization. Peripheral inflammatory mediators play a major role in generation and perpetuation of chronic oral pain conditions in pets. Host-mediated pro-inflammatory cytokines and chemokines are mobilized at the diseased site from host cells in response to bacterial antigens. Peripheral sensitization is initiated when compounds like histamine result in vasodilation, allowing these proalgesic mediators to extend to previously non-inflamed tissue. Alteration of this effect is achieved by decreasing the production of some of these substances by using NSAIDs to dampen host response.
Opiate-receptor activation. The brain attempts to counter the number and intensity of pain signals reaching the higher centers by initiating the production of internal opiates?— endorphins, dynorphins and enkephalins — to occupy opiate receptors on nerves, bone, gingiva and other cell types. Unfortunately, these do not produce adequate analgesia in many chronic pain states. Use of synthetic opiates including morphine, fentanyl and hydromorphone in CRI and client-administered home care bridges the therapeutic gap left by the descending inhibitory opiates.
Intraoperative physiologic benefits. Not only does CRI initiate the desired goals of altering wind-up, decreasing inflammation and stimulating opiate receptors, it also decreases the amount of inhalant anesthetic needed during the intraoperative period. Maximizing this effect with the addition of complete sodium channel blockade ensures that ascending sensory signals are eliminated. This is accomplished by using regional nerve blocks.