Managing pain during an anaesthetic 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/ diarrhoea and dysphoria. The adverse effects of mu opioids are dose dependent and can be limited with use of a multimodal approach.
When the anaesthetist 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 anaesthetist 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.