Numerous chemicals react to increase the sensitivity of these neurons, exaggerating the frequency and intensity of nociception.
Glutamate is partly responsible, in that it acts to bind to the NMDA receptor on the wide dynamic range neuron, making it
a primary substance involved in central hypersensitization (Figure 2).
Figure 2: Binding to the NMDA receptor on the wide-dynamic-range neuuron, glutamate becomes a primary substance involved
in central hypersensitization.
Drugs that bind preferentially to the NMDA receptor in the nucleus caudalis can help us manage central sensitization associated
with oral pain states. Traditional pain medications will not be effective for this component of chronic pain. NMDA antagonists
and other analgesic agents will be covered in the third part of this series.
Pre-emptive analgesia is the administration of analgesics prior to a painful stimulus, to decrease the anticipated post-stimulus
pain. Administering analgesics prior to inducing a painful stimulus is more effective than giving the same drug after the
stimulus is induced. Once established, especially when central sensitization is involved, pain becomes very difficult to control,
emphasizing the importance of providing pain management preoperatively.
Some common conditions of chronic severe oral pain, such as feline LPGS, refractory stomatitis in dogs and oral cancer, all
should receive special attention in preoperative pain management. Failure to do so will make it likely that management will
be very difficult post-operatively, requiring additional hospitalization, additional administration of injectable analgesics
and feeding assistance. Figure 3 outlines the result of a pre-emptive analgesic given to prevent central and peripheral sensitization.
Figure 3: Preoperative pain management is recommended in some instances. This outlines the result of a pre-emptive analgesic
given to prevent central sensitization.
Multimodal pain management is defined as use of two or more analgesics in combination to minimize or eliminate patient pain.
Often this approach allows the practitioner the luxury of decreasing the dose for each analgesic, making the combination safer
than a higher dose of a single agent. Using different analgesics in this multi-modal manner allows clinicians to block pain
in different portions of the pathway of nociception. Table 1 demonstrates the effect of different drug classes on transduction,
transmission and modulation. As you can see, the local anesthetics block pain in all three nociceptive pathways.
Table 1. Drug classes affecting varying portions of the nociceptive pathway
Manipulation of the environment is important in providing maximal comfort for painful patients postoperatively. Monitoring
patient temperature is particularly essential in oral surgery. All patients, but particularly small ones, are subject to cooling
from the cool-water spray from ultrasonic and high-speed devices.
Intravenous fluids should be properly warmed and safe external warming devices utilized to maximize patient comfort and minimize
intraoperative hypothermia. During recovery, warm towels and blankets should be used continually for comfortable padding.
To decrease postoperative stress, consideration should be given to separating dogs and cats or even isolating individual patients.
Noise should be minimized. Verbal and tactile interaction with patients can be comforting in some, whereas others recover
better with passive observation. Soothing music also may be beneficial.