Pain or Dysphoria?
By Bonnie Gatson DVM DACVAA
It’s easy to envy human physicians who can ask their adult conscious patients, “How are you feeling?” or “What is your pain level on a score from 1 to 10?”. Unfortunately, veterinarians are not afforded this luxury, which can lead to extremely frustrating clinical guessing games.
One of the more common exasperating post-operative decisions can be differentiating between pain and anesthesia-related dysphoria. We have all experienced an animal waking up from anesthesia thrashing around violently, with staff jumping on top of the animal screaming at the top of their lungs to bring on the sedatives. It seems pretty easy to guess that an animal like this is experiencing emergence delirium, a form of anesthetic-related dysphoria. However, it can be harder to differenitaite pain from dysphoria when the recovering patient is quietly but relentlessly whining. These are the cases that become clinical conundrums.
Dysphoria is profound state of unease due to extreme agitation and anxiety. Clinical signs of dysphoria include vocalization, panting, difficulty settling down, and restlessness. Importantly, animals with dysphoria may not be mentally appropriate, they may urinate, defecate or salivate without control, and efforts to contain or provide comfort to these animals will prove futile.
Pain is defined as an “unpleasant sensory or emotional experience caused by actual or perceived tissue damage.” Pain scales have been developed for dogs and cats based on behavioral signs of pain and changes in body posture and facial expression. These scales usually involve the subjective observations of an individual using specific behavioral cues and translating this into a numerical scale. The use of behavior-based pain scales allows the observer to objectively monitor progress and response to treatment while increasing awareness among staff members regarding the importance of monitoring for pain. However, depending on the pain scale, it is possible to obtain an erroneous number (either too high or too low) when the animal is also exhibiting dysphoria or other mentally inappropriate state.
There are a number of psychomotor indicators of pain in dogs and cats which can be found in the table below.
The assessment of pain in cats can be exceptionally difficult as cats are often more stoic and better adapted to hide behavioral signs of pain compared to dogs. When assessing a cat’s pain status, variables such as posture, orientation in a cage, facial expression, loss of normal behaviors including appetite, and response to palpation of a surgical site should be evaluated. Given the fact that cats are often more resigned when in pain, it may be easier to differentiate pain from dysphoria in this species. Post-operative dysphoria is often demonstrated in cats as restlessness, bumping into the walls of the cage and rolling uncontrollably, potentially demonstrating extremely aggressive behaviors, while vocalizing, urinating and/or defecating. What becomes more of a challenge in this species is differentiating between a cat that is resting comfortably post-operatively from a cat that is painful. In this case, facial markers, body posture, orientation in the cage, and willingness to interact with staff may help differentiate between the two.
TREATING DYSPHORIA
In a situation where the patient or staff may be hurt, a very small dose of propofol 0.5 - 1 mg/kg can stop dangerous emergence behavior. However, careful titration is necessary and the supplies to reintubate should be available in case apnea occurs.
If recent opioid administration is suspected to be the cause of dysphoria, reversal with low doses of butorphanol (kappa agonist-mu antagonist opioid) or naloxone can be considered. It is important to note that reversal of full-mu opioid agonists is not advised for animals with painful conditions without providing an alternative means of analgesia. This is where butorphanol may have a slight advantage: it can provide MILD analgesia while reversing unwanted effects of full-mu agonist opioids. Either drug should be diluted and titrated just to effect. It is important to note that both butorphanol and naloxone have short half-lives and therefore the effects of the full-mu agonist opioid may reappear once the plasma concentration of the reversal agent begins to wane. If an animal with a painful condition is dysphoric with opioid administration, an alternative analgesic plan (regional anesthesia, alpha-2 agonists) must be formulated.
Sedatives are commonly employed to treat anesthetic-related dysphoria and may be particularly helpful when pain cannot be ruled out as the cause of the behavioral abnormality. Acepromazine can be used in very small doses, ~0.005-0.01 mg/kg IV. Acepromazine causes vasodilation and hypotension due to its antagonism of alpha-1 receptors and therefore should be used judiciously in patients where hypotension should be avoided. It is important to note that acepromazine often provides minimal and unreliable sedation to cats, but provides more effective sedation to dogs especially when combined with an opioid. Acepromazine has no analgesic properties and is not reversible unlike dexmedetomidine. Dexmedetomidine in microdoses, ~0.5-2 mcg/kg (0.0005-0.002 mg/kg), can also be used to treat dysphoria. Dexmedetomidine can cause initial vasoconstriction and bradycardia followed by hypotension. If patients remain agitated, either this initial bolus can be repeated or an infusion of dexmedetomidine can be utilized at ranges between 0.5-4 mcg/kg/hr. The infusion should be started at a low rate and titrated to effect. Dexmedetomidine can cause diuresis, and therefore a urinary catheter may be required for prolonged infusions, especially if the animal is too sedate or agitated to be walked outside. Benzodiazepines, although they produce minimal cardiovascular side effects, have the potential to create paradoxical excitation and are often avoided when choosing a sedative agent to treat post-anesthetic dysphoria.
Another option to treat anxious or dysphoric animals is trazodone, a serotonin antagonist and reuptake inhibitor. Trazodone is an oral drug used at a dose of 3-10 mg/kg twice daily. The onset of this drug is fairly rapid in dogs, around 1-2 hours. When starting trazodone, it is recommended to start low and increase the dose until the desired effect is observed. This drug has been shown to reduce anxiety-induced behaviors in hospitalized dogs.
IF I’M NOT SURE IF IT IS PAIN OR DYSPHORIA, WHAT SHOULD I DO?
An initial physical examination is in order with emphasis placed on mentation, cardiorespiratory parameters, observation of abnormal behaviors, and palpation of the surgical site. Recent anesthetic history and administration of analgesic agents, especially opioids, should be noted. If tolerated, any suspected painful area should be palpated and observed for a reaction while comparing this to palpation of another non-painful region. Animals that are dysphoric can exhibit inappropriate behaviors regardless of the area palpated. If the behaviors initiated following opioid administration, this should also increase suspicion for dysphoria.
If the diagnosis remains unclear and a painful process exists, treating for pain with short acting full-mu agonist opioids is helpful to differentiate between the two conditions. Observe behaviors following administration of a small fentanyl bolus (2 mcg/kg IV). At this point, if the problematic behavior continues or worsen following an opioid bolus, a sedative agent such as acepromazine or dexmedetomidine can be administered or you may consider reversal of the opioid, if the animal has a non-painful condition.