In human medicine, pain is considered the fifth vital sign, ranking as important as pulse, respiration, temperature, and blood
pressure. Pain also continues to gain attention in veterinary medicine as an important vital sign. Pain can have many negative
side effects in our patients, including tachycardia, hypertension, immunosuppression, delayed wound healing, exhaustion, and
inappetence.1
However, most technicians and veterinarians lack current knowledge of common analgesics, local anesthetic agents, and adjunctive
analgesics with regard to their pharmacology, duration of action, and cost. Educating veterinarians and technicians with regard
to the affordability of these drugs and their actions should increase multimodal analgesia in single-doctor and multidoctor
practices, resulting in better pain management for postoperative patients.
Assessing pain
Unfortunately, our patients cannot tell us when they are experiencing pain, so we must learn to watch and listen to our patients.
Patients experiencing pain will exhibit many behavioral changes, including guarding or biting of the surgical site, aggression,
or a frequent changing of positions. Some patients will assume a prayer-like position, especially after postoperative abdominal
or thoracic surgery.
Many pain scoring techniques are available in veterinary medicine, and they can be helpful tools when implemented correctly.
But ultimately, it is the technician's responsibility to observe changes in both the patient's behavior and vital signs and
to notify the veterinarian of any clinical signs of pain. It is also our duty as technicians and veterinarians to educate
owners about these signs so their pets can comfortably convalesce at home.
Understanding pain pathways
The pain pathway consists of four processes: transduction, transmission, modulation, and perception.
1. Transduction is the site at which a painful (noxious) stimulus occurs and is converted into an electrical signal that will be transmitted
to the central nervous system (CNS) through afferent nerves (nerves that carry electrical signals toward the CNS).
2. The transmission portion of the pathway involves peripheral nerves that send the noxious stimulus to the dorsal horn of the spinal cord, then
through the spinal cord, and finally to the brain. These peripheral nerves contain both afferent and efferent (nerves that
carry the electrical signal away from the CNS) nerves.
3. Modulation alters the noxious signal; i.e., the signal is either amplified or suppressed. Modulation occurs in the spinal cord as well
as the brain.
4. Finally, during perception, the brain deciphers the information that it has received and interprets that information as pain.
Figure 1: Diagram of the canine nervous system. (Dorling Kindersley/Thinkstock)
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Figure 1 shows the different pain pathways as well as the analgesics, nonsteroidal anti-inflammatory drugs (NSAIDs), and local
anesthetics that can be administered to treat pain at different points in the pathway. (Note: Several other drugs that affect
the pain pathway are beyond the scope of this article. These drugs can be located in current anesthesia and pain management
textbooks.)
Disruption along the pathway occurs when analgesics, NSAIDs, and local anesthetic agents are used. Multimodal pain management
targets several of these pathways at the same time, resulting in better analgesia. NSAIDs are an important part of multimodal
analgesia, and many articles have been written on their positive contributions. They should be considered when developing
a postoperative multimodal pain management strategy. However, this article will limit discussion to the economical cost of
different opioids, local anesthetic agents, and adjunctive analgesics and how these drugs contribute to better analgesia than
what is currently being used in many small and large veterinary practices.
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