11 Jun 2024
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In late 2022, an updated and refreshed version of the WSAVA guidelines for the recognition, assessment and treatment of pain was published by the WSAVA Pain Committee.
These guidelines form a very comprehensive document describing all aspects of pain management in cats and dogs; importantly, they are free to download from the Journal of Small Animal Practice at bit.ly/4c1viyL and the WSAVA website at bit.ly/4c2OYmd making them accessible to every veterinary practitioner worldwide.
They have already been translated into six different languages (Arabic, Mandarin, Thai, Portuguese, Spanish and Russian) and more translations are planned for the near future. The guidelines are divided into three sections.
Section one focuses on the pathophysiology of different types of pain (for example, inflammatory pain, maladaptive pain, cancer pain), as well as emphasising the importance of accurate recognition and quantification of acute, and chronic, pain in cats and dogs. It describes in detail the different tools available to quantify acute and chronic pain, and provides weblinks to the tools that are freely available online.
Section two describes the pharmacology of the drugs that can be used to provide analgesia in animals and their respective advantages and side effects. Recommended dose ranges are provided and clinical questions that often arise around the use of analgesic drugs are answered (for example, how can I practically switch an animal from one NSAID to another?).
Section three provides analgesic protocols and approaches for the management of different surgical and medical conditions in cats and dogs. This section is designed to be practical and accessible to all veterinary practitioners worldwide, for example, providing drug protocols that can be used in areas of the world where opioids are not freely available to treat veterinary patients.
The aim of this article is to focus on section three of the pain guidelines, highlighting recommendations for the treatment of pain associated with common surgical and medical conditions in cats and dogs.
Fortunately, in the UK, veterinary licensed opioids are available for the treatment of pain; therefore, protocols involving opioid administration will be highlighted.
The severity of pain associated with castration and ovariohysterectomy in cats (Figure 1) is closely related to the degree of surgical trauma; therefore, careful tissue handling and adherence to good surgical principles are recommended.
Many different protocols can be used to provide analgesia and anaesthesia for cats undergoing castration and ovariohysterectomy. The use of alpha-2 based protocols have now become very popular for neutering in the UK, and a combination of an opioid, alpha-2 agonist and ketamine will provide premedication, induction and maintenance of anaesthesia, although, facilities should be available to extend the duration of anaesthesia if necessary.
Intubation might not always be necessary for short procedures such as castration in cats, although oxygen should always be supplemented by face mask if intubation is not carried out and the facilities to intubate should be available if necessary. Data comparing the analgesic efficacy of different opioids for neutering are conflicting, with some studies showing no difference between butorphanol, buprenorphine and methadone (Bortolami et al, 2013; Slingsby et al, 2015), while another study showed methadone to provide superior analgesia to buprenorphine in cats undergoing ovariohysterectomy anaesthetised with the QUAD (opioid, midazolam, medetomidine and ketamine) protocol (Shah et al, 2019).
Differences in results likely relate to timing of NSAID administration and whether cats undergoing both castration and ovariohysterectomy or just ovariohysterectomy were considered in the study design. Generally, butorphanol is considered to provide poor analgesia in cats and dogs, and is short acting; therefore, longer-acting opioids such as methadone and buprenorphine are preferred for neutering in both cats and dogs.
Local anaesthetic techniques are recommended for both castration – intratesticular nerve block with lidocaine (Moldal et al, 2013) – and ovariohysterectomy, with incisional and intraperitoneal blocks with bupivacaine (Benito et al, 2018; Steagall et al, 2020).
NSAIDs are pivotal to perioperative analgesia for neutering in cats, although some debate exists about the duration of NSAID analgesia required after neutering surgery, with one study suggesting that three days’ analgesia is necessary after ovariohysterectomy (Väisänen et al, 2007) and another suggesting that a single dose of an NSAID at the time of ovariohysterectomy is sufficient for most cats (Hillen et al, 2023).
The recommendations for castration and ovariohysterectomy in dogs are very similar to those in cats, with similar drug protocols being suitable for the different species. One study has compared the efficacy of methadone and buprenorphine for ovariohysterectomy in dogs, and found methadone to be superior to buprenorphine for this procedure (Shah et al, 2018).
Similar local anaesthetic techniques are appropriate for neutering in dogs as in cats, and use of these is to be encouraged as they will reduce the amount of maintenance agent required to maintain anaesthesia and provide postoperative analgesia for a number of hours after surgery.
Orthopaedic surgery (Figure 2) is generally associated with moderate to severe pain in cats and dogs, and general anaesthesia for these procedures is a prerequisite.
Analgesia protocols should be based on the principles of multimodal analgesia (the practice of using analgesics from different drug classes in combination) and preventive analgesia.
Preventive analgesia is a principle that has replaced the concept of pre-emptive analgesia and involves the administration of analgesic drugs early (ideally before the onset of pain) and for sufficient time to prevent the onset of central sensitisation (Pogatzki-Zahn and Zahn, 2006). It is important to distinguish multi-modal analgesia from uncontrolled polypharmacy; the different classes of drugs selected should ideally be based on knowledge of underlying pain mechanisms.
As with all inflammatory pain conditions, NSAIDs form the cornerstone of analgesic regimens, but attention should be paid to potential side effects and contra-indications in some patients – particularly when cardiovascular instability is expected during anaesthesia.
Local anaesthetic techniques are also pivotal, and most orthopaedic surgeries can use a regional anaesthetic technique to help with intraoperative and postoperative analgesia blocks (for example, epidural or femoral and sciatic nerve blocks for hindlimb procedures, brachial plexus, RUMM [radial, ulnar, median and musculocutaneous]) for forelimb procedures. These blocks are described with illustrations in the WSAVA pain guidelines.
Premedication with methadone has been shown to provide superior analgesia to premedication with buprenorphine in dogs undergoing orthopaedic procedures (Hunt et al, 2013). Intraoperative analgesia can be supplemented with opioid infusions – for example, a fentanyl continuous rate infusion (CRI), a ketamine CRI or a lidocaine CRI, although lidocaine CRIs for analgesia are not recommended in cats due to the negative effects on haemodynamics (Pypendop and Ilkiw, 2005).
Postoperative analgesia should comprise opioids, generally for at least 24 to 48 hours, NSAIDs for days to weeks and adjunctive therapies like cold (Wright et al, 2020) and physical rehabilitation. Paracetamol might also play a role in perioperative analgesia for orthopaedic surgery in dogs.
Quantification of pain using validated pain scoring tools such as the Short Form of the Glasgow Composite Pain Scale-Canine for dogs (Testa et al, 2021) or the Glasgow Composite Pain Scale-Feline (Calvo et al, 2014) or Feline Grimace Scale (www.felinegrimacescale.com) for cats is essential to ensure that postoperative analgesia is adequate, avoiding the potential for both over or underdosing of analgesics.
The optimal duration of analgesia after major orthopaedic surgery in both cats and dogs is unknown – especially once animals are discharged to their carers. Educating carers about signs of pain in cats and dogs can be helpful to ensure that analgesia is sufficient in the postoperative period.
The term “medical pain” encompasses conditions not primarily associated with surgery or trauma, and can comprise a wide variety of conditions, many of them involving visceral pain.
Visceral pain is recognised to be difficult to localise (probably due to the phenomenon of referred pain) and diffuse in nature, and can arise from enlargement of solid organs, inflammation of any organ (for example, pancreatitis) or distention of hollow organs, such as the gut.
Obviously, the goal of therapy is to treat the underlying medical complaint, but analgesics should be given at the same time to ensure the comfort of the animal during diagnosis and treatment. Opioids form the mainstay of treatment for medical conditions, but it is important to avoid opioids that are more associated with emesis, such as morphine, and to be aware that both buprenorphine and methadone can be associated with nausea. This is commonly seen as excessive salivation after opioid administration to both cats and dogs (Figure 3), and may be managed by the administration of an anti-emetic such as maropitant (Hay Kraus, 2017).
Placement of an intravenous catheter for the administration of opioids avoids the need for repeated intramuscular or subcutaneous injections of opioids that can be painful and stressful for the animal. NSAIDs are contra-indicated in animals that are haemodynamically unstable, have acute kidney injury or gastrointestinal comprise. Paracetamol might be an alternative option for dogs when NSAIDs are contra-indicated.
Neuropathic pain (Figure 4), caused by damage to the somatosensory nervous system, is recognised to be extremely difficult to manage effectively in both humans and animals.
It is always maladaptive and is underpinned by changes in the central nervous system, leading to hyperalgesia and allodynia, which are extremely unpleasant for the animal (Adrian et al, 2017). Gabapentinoids (gabapentin or pregabalin) have been used as the first line treatment for neuropathic pain in cats and dogs, with some studies reporting an improved quality of life following administration (Plessas et al, 2012; Plessas et al, 2015).
Oral N-methyl-D-aspartate (NMDA) receptor antagonists such as amantadine or memantine might also be effective for the management of neuropathic pain because of their ability to down-regulate the NMDA receptor, which plays a key role in the onset and maintenance of central sensitisation. Only one study has investigated the analgesic efficacy of amantadine in dogs. This study investigated amantadine 3mg/kg to 5mg/kg once daily in dogs with osteoarthritis pain that was refractory to NSAIDs and found that dogs receiving amantadine and meloxicam had lower owner-assessed pain levels compared to administration of meloxicam alone (Lascelles et al, 2008).
One study has investigated the use of amantadine (5mg/kg once daily) in cats with osteoarthritis and found that although amantadine reduced activity, it improved owner perceived scores of mobility and quality of life (Shipley et al, 2021).
Recently, a trend has emerged towards low-dose SC administration of ketamine for osteoarthritis pain in dogs and cats, although to date no studies support this practice. Animals presenting with severe signs if neuropathic pain might require hospitalisation for IV therapy with opioids, ketamine or lidocaine administered by CRI, although lidocaine CRIs should be used cautiously in cats due to haemodynamic compromise.
The WSAVA 2022 pain guidelines provide a comprehensive, evidence-based, state-of-the-art overview of current recommendations for the recognition, assessment and treatment of pain in cats and dogs.
Great advances have been made in pain assessment tools for cats and dogs in the past 10 years, with robust validated tools now freely available to the veterinary practitioner for use in clinical practice. The availability of licensed drugs has also increased in the UK, which is fortunate to have a wide repertoire of licensed opioids and NSAIDs available for use, making it easier to provide adequate analgesia for small animals experiencing mild to moderate to severe pain. Scan the QR code for WSAVA guidance.
Clinical Assist