Managing pain during an anesthetic event is integral to veterinary patient care and recovery, and can be achieved via multiple modalities. Pure mu opioids, the foundation of pain management, induce a wide spectrum of positive and negative effects in animals. Aside from managing pain, positive effects of mu opioids include sedation and a sense of euphoria; negative effects can include nausea, vomiting/diarrhea and dysphoria. The adverse effects of mu opioids are dose dependent and can be limited with use of a multimodal approach.
When the anesthetist is faced with managing adverse effects of mu opioid administration, an understanding of the differences between analgesia, pain and dysphoria can guide the appropriate intervention and outcome.
Analgesia, pain and dysphoria defined
Analgesia is defined as the lack of a response to painful or noxious stimuli while in an awake state. The interruption of painful stimuli is integral to veterinary patient care, comfort and recovery.1 One of the ways analgesia can be achieved is via administration of opioids and interruption of the pain pathway.
Pain is a noxious stimulus that potentiates a cascade of events. Untreated pain provokes myriad unwanted physiologic responses such as anorexia, self-trauma, central sensitization and maladaptive behaviors, all of which prolong recovery and add unnecessary stress.1 Stress drives the sympathetic nervous system, which activates the flight or fight response.
Pain is unique to each patient and exists in different capacities, including chronic arthritic pain, neuropathic pain, acute pain and traumatic pain. Because further complications can arise when more than one type of pain is present, the anesthetist must simultaneously plan for pain related to chronic problems and anticipate acute pain. For example, an older patient with arthritic hips that is going to be positioned for an abdominal exploratory requires hip support in addition to systemic analgesia.
Dysphoria, a feeling of discomfort or unease, often occurs with administration of pure mu opioids. Co-administration of anesthetics, underappreciated pain or underlying behavioral issues can factor into the development of dysphoria.2 Of note, administration of opioids in painful canine and feline patients is less likely to promote dysphoria, nausea and vomiting.
Rapidly delivered intravenous opioids—even at clinically appropriate doses—may promote excitement, which is generally brief and typically resolves without intervention.2 By comparison, dysphoric patients are vocal, disruptive, and inconsolable.3 An inconsolable patient does not respond to interaction. The dysphoric patient may be bradycardic, disinterested in food or water, and the third eyelids may be visible. Dysphoria can also be accompanied by anxiety, distress, or agitation.4
Treatment
A systematic approach is recommended when determining whether pain versus dysphoria is present. If the anesthetist is uncertain about which treatment is indicated, pain should be ruled out first. A dysphoria management algorithm (Figure 1) provides treatment direction and options.
Treating dysphoria can partially to completely antagonize the untoward effects of pure mu opioids (Table 1). High doses of naloxone will antagonize the central effects of opioid agonists that may cause the animal to experience acute pain and associated sympathetic stimulation with serious consequences that include tachycardia, hypertension, pulmonary edema and cardiac arrhythmias. It is best to administer naloxone to effect by careful titration, keeping in mind that multiple doses may be needed to maintain antagonistic effects due to its short duration of action.2
A common misconception about the painful or dysphoric patient is that the necessary intervention is a sedative or anxiolytic. Administering a sedative to a dysphoric patient does not resolve the dysphoria and potentially compounds existing problems (Fairfield, AF, personal communication, October 3, 2019). Similarly, painful patients will not be comfortable or euphoric after receiving a sedative. Table 2 details appropriate interventions after pain and/or dysphoria is treated or ruled out.
Complicating factors that may lead to difficult recoveries include older patient age and pre-existing anxiety. Interaction with and handling by the veterinary team, as well as the increased noise and lights inherent to a veterinary hospital setting, can also lead to rough recoveries. Interestingly, a having a full bladder can lead to a rough recovery as well.6
This dog shows classic signs of dysphoria following a surgical procedure: visible third eyelids, open mouth due to panting and the need for full body support by the technician.
In this video, the same dog has been treated with butorphanol (inset), and her eyes have rotated centrally, the third eyelids are no longer visible and she can hold her head up.
References
1. Morgaz J, Navarette P, Muñoz-Rascón P, et al. Postoperative analgesic effects of dexketoprofen, buprenorphine and tramadol in dogs undergoing ovariohysterectomy. Res Vet Sci 2013;95(1):278-282.
2. Grimm KA, Lamont LA, Tranquilli WJ, et al. Veterinary anesthesia and analgesia: The fifth edition of Lumb and Jones. 5th ed. 2015 Ames, IA: Wiley-Blackwell; 2015.
3. McPartlin AM. Identifying pain vs dysphoria.Presented at Turtle Mountain Veterinary Clinic, Bottineau, North Dakota; 2016.
4. Krein S. Pain vs. dysphoria. MSPCA Angell website: mspca.org/angell_services/pain-vs-dysphoria/. Retrieved February 13, 2020.
5. Plumb DC. Plumb’s veterinary drug handbook. 5th ed. Ames, IA: Wiley-Blackwell; 2011.
6. Palmer, D. Managing rough recoveries. Presented at the 2019 Anesthesia Nerds Symposium, Western Veterinary Conference.Las Vegas, NV; October 2019.
Download Issue : Vetted March 2020