Analgesia methods and techniques in veterinary medicine have evolved rapidly over the last few decades. This is partly due to the increased availability of new medications and partly due to a more comprehensive understanding of pain physiology and its adverse effects on veterinary patients.
The sensation of pain is a complicated physiological and emotional experience. Pain management is a critical aspect of animal well-being and it is vital that analgesia is provided when required. This allows for smooth recovery following surgery, offers relief from injuries and painful chronic conditions, and generally provides a good standard of animal welfare.
Multimodal analgesia is a useful and effective pain management strategy in veterinary medicine. It involves the combination of medications from different classes of drugs and other pain-relieving techniques. A multimodal approach aims to maximise pain relief while minimising side effects from any single medication. This is achieved by targeting different steps in the pain pathway.
A multimodal approach aims to maximise pain relief while minimising side effects from any single medication
The implementation of multimodal pain management to alleviate pain is not only ethically imperative but also therapeutically advantageous. There is plenty of evidence to highlight the detrimental effects of pain on recovery and morbidity in patients. Surgery is a frequent source of pain, which is why adequate perioperative anaesthetic and analgesic techniques are so important.
Understanding pain pathways
The pain pathway involves many different neurotransmitters and receptors. This means there are multiple targets for analgesic drugs.
All vertebrates are capable of experiencing pain when tissue damage occurs. The perception of pain involves a complicated interaction between the central and peripheral nervous systems. Pain occurs when tissues are injured, triggering a release of inflammatory mediators. These mediators activate nociceptors, which transmit pain signals along the afferent nerve fibres to the spinal cord and brainstem. The pain signals are then relayed to the parts of the brain that are responsible for the perception of pain and the emotional response to pain.
There are many different types of pain; the most common types include acute, chronic, neuropathic and cancer pain.
- Acute pain: this is a rapid and usually intense response to a noxious stimulus. It gives a signal that there is potential tissue damage. It is usually self-limiting and resolves once the stimulus has gone or the healing process begins
- Chronic pain: this can last for an extended duration of time. It does not serve a protective function and causes discomfort and stress. It is a disease of altered neuroprocessing
- Cancer pain: this encompasses a spectrum of acute, chronic or intermittent pain experiences that arise from either primary tumours, metastatic spread or the side effects of cancer treatment modalities such as chemotherapy and radiation. It is important to understand the source of the pain foreffective pain management
- Neuropathic pain: this type of pain arises from damage to the actual nervous system itself, as opposed to the tissues it normally serves. Causes include trauma, vascular injury, infections or endocrine issues such as diabetes
There are two main pain pathways. These are:
- Nociceptive pain: this is experienced as a result of direct damage to the tissues. It is typically acute and well localised. It is mediated by A-delta and C-fibre nerve fibres
- Neuropathic pain: as described above, this is a result of damage to the actual nervous system. It is usually experienced as shooting, burning or tingling pain
Nociceptive pain usually responds well to conventional analgesia methods whereas neuropathic pain typically does not.
Methods of analgesia
A wide variety of analgesic medications are available for use in small animal veterinary medicine. These include but are not limited to:
- Non-steroidal anti-inflammatory drugs (NSAIDs): NSAIDs work by inhibiting the production of the enzyme cyclooxygenase (COX). This enzyme is required to convert arachidonic acid into thromboxanes, prostaglandins and prostacyclins. The results seen from the use of NSAIDs are down to the reduction in these compounds. Examples of NSAIDs commonly used in veterinary medicine include meloxicam, carprofen and firocoxib
- Opioids: opioids are strong painkillers that bind to opioid receptors primarily located in the dorsal horn of the spinal cord and the brain. They prevent pain signals from reaching the brain. Opioids are involved in the inhibition of both ascending and descending pathways. Morphine, fentanyl and buprenorphine are some examples of opioids used in veterinary pain management
- Local anaesthetics: local anaesthetics block sodium channels in nerves, therefore preventing nerve conduction at the site of administration. This provides pain relief in the specific area it has been administered. Lidocaine, bupivacaine and ropivacaine are examples of local anaesthetics used in veterinary medicine
- Alpha-2 adrenergic agonists: these medications stimulate alpha-2 adrenergic receptors in the central nervous system and spinal cord, therefore modulating pain perception. Examples include dexmedetomidine and medetomidine
Non-pharmacological interventions
It is easy to overlook the significance of non-pharmacological interventions when thinking about pain relief. Non-pharmacological interventions play an important role in a multimodal pain management plan. These techniques can help improve comfort, promote healing and alleviate pain. Non-pharmacological interventions include:
- Physical therapy: many physical therapy techniques such as massage, acupuncture and laser therapy improve mobility, reduce inflammation and promote pain relief
- Behavioural management: techniques such as positive reinforcement and redirection can help to minimise behaviours associated with stress, anxiety and pain
- Environmental enrichment: ensuring the patient is comfortable and content in their immediate environment can help reduce stress and anxiety. This can alter the way they perceive pain
- Nutritional support: it is so important to ensure patients are fed a balanced diet with all the correct nutrients. This is essential for healing and can also influence pain sensitivity
It is easy to overlook the significance of non-pharmacological interventions when thinking about pain relief
The multimodal approach
The implementation of multimodal pain management strategies represents a significant advancement for veterinary patients. Advantages include:
- Optimal pain relief: the combination of different drugs that have different mechanisms of action allows different aspects of the pain experience to be targeted. This means the pain is more effectively controlled
- Reduction of side effects: using a multimodal approach often means that lower doses of each drug can be administered. This can minimise the risk of side effects associated with individual drugs
- Different types of pain can be addressed: the use of multimodal pain management means that neuropathic and nociceptive pain can be addressed to achieve a better result for the patient
- Improved patient recovery: effective pain management promotes better healing as comfortable animals can rest properly and participate in physical therapy more actively. If a patient is experiencing less stress due to not being in a great deal of pain, the chances of them having a successful recovery are higher. Patients are more likely to be able to move around if they have a good analgesic protocol in place. This is important for maintaining muscle mass and strength and preventing complications such as skin sores, pneumonia or urinary tract infections
Final thoughts
The beauty of this approach is that each patient receives a tailored protocol that addresses their individual needs
The mechanisms involved in nociception are complex and intricate. It is a sensible approach to use a combination of different analgesic drugs that function in different ways to achieve a satisfactory level of analgesia. A multimodal approach uses a diverse selection of drugs and non-pharmacological interventions to target pain at multiple levels. The beauty of this approach is that each patient receives a tailored protocol that addresses their individual needs and can be adjusted according to their response to the pain they are experiencing.
