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.
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.
The most common oral condition in which pain is an occult component is periodontal disease. Client education is paramount
to achieving compliance. Inflammation and odor indicate infection. Cleaning the patients' teeth does little to solve the underlying
periodontal infection. We must stress to clients that we are treating infection rather than cleaning teeth. Pictures can be
used to demonstrate what hides beneath the gum line causing pain (Photos 1 and 2).
Photo 1: Images like these can be used for client education to demonstrate pain below the gumline. Without dental radiography,
this patient likely would just have had teeth cleaned, and the true pathology below the gumline would have been missed.
CRIs and post-operative analgesics
Many practitioners already recognize the importance of treating chronic oral pain and currently use the chronic pain analgesic
triad. CRIs target various mechanisms of pain generation and perpetuation and are used pre-operatively and continued variably
into the post-operative period. Post-operative pain management administered by clients should provide continued coverage
using similar compounds targeting the same mechanisms. While a discussion of the pathophysiology of pain is beyond the scope
of this manuscript, three primary components represent the targets of CRI and home-based client-administered pain management.
These include central sensitization alteration (wind-up), opiate-receptor activation and peripheral inflammation attenuation.
Photo 2: Radiographically severe bone loss in the furcation of the right maxillary fourth premolar is present. This patient
was noticeably more active following extraction.
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
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
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.