Acute pain in small animals: how far have we come and where are we going?

The inclusion in this edition of the Journal of Small Animal Practice of a review article (Gurney, 3) and two original research studies (Gurney et al., 4; McMillan et al., 6) on the subject of acute pain management in small animals, emphasizes the significant advances we have made in the past few years in terms of both appreciating pain as a significant issue in our patients, and also highlighting the increasing array of pharmaceutical modalities now available for its treatment. We do have to recognize, however, that this pro-active approach to pain has not always been so obvious in veterinary practice. Looking back at published research from the 1990s, numerous papers highlight the fact that analgesics were dramatically under-used in animals for the management of acute pain. For instance, Dohoo and Dohoo (2) identified that less than 50% of Canadian small animal veterinarians routinely provided analgesic therapy following surgery. It would be all too easy to put this down to the fact that veterinary surgeons in general practice were simply not following the direction of opinion leaders in centres of academic excellence. However, this is refuted by a study conducted by Hansen and Hardie (5) that retrospectively analysed the use of analgesic drugs in animals undergoing various operations at North Carolina Veterinary School. Despite including surgical interventions such as thoracotomy, limb amputation and fracture repair, only 40% of dogs received any post-operative analgesic therapy during their time in the hospital. Thus, it would appear that even in ‘advanced’ practice settings, appropriate analgesia was not being provided at that time. Both of these studies relate to North American veterinarians and thus do not provide evidence of similar issues on this side of the pond, but neither does it refute that they existed. Indeed, Capner and others (1) reinforced the under-utilisation of analgesics in UK general practice, while additionally showing that there was a significant effect of decade of graduation on whether a veterinary surgeon would prescribe analgesic therapy in defined situations, with more recently qualified veterinarians being more likely to administer analgesia. The logical conclusion was that management of acute pain in animals was likely to improve as the pool of older veterinarians became diluted by younger graduates, and, indeed, this appears to be the case, with administration of analgesia now largely ‘routine’ in small animal practice. The advances in small animal analgesia that have occurred over the past decade or so have mirrored the explosion in the number of agents available and licensed for veterinary use as part of acute pain management. Within the past year, a novel veterinary formulation of fentanyl has received a pan-European Union licence for dogs, and methadone has also gained UK marketing authorisation in this species. In even greater numbers, we have a widening array of non-steroidal anti-inflammatory drugs, which bring with them improved safety profiles. There is also increasing use of analgesic adjunct drugs agents which, by themselves, offer limited analgesic efficacy, but which are synergistic with the more ‘traditional’ analgesic drugs. Thus, it would seem there is no shortage of licensed and ‘safe’ agents with which we can improve management of acute pain. Interestingly (or, perhaps, pedantically), although we refer to all of the above drugs as ‘analgesics’, the term ‘analgesia’ is actually defined as “absence of pain” (Collins English dictionary). While there is no doubt that the drugs we use will help reduce a patient's perception of pain, perhaps they should be more appropriately termed ‘hypoalgesics’ (although nobody actually uses this descriptor), as they seldom lead to complete obliteration of pain unless they render the animal unconscious (bearing in mind that pain is a conscious phenomenon, and, therefore, can only be appreciated by ‘awake’ patients). As such, the only drugs that are truly ‘analgesic’ are the local anaesthetic agents, as these are the only ones that can completely block pain transmission and, therefore, perception. The review article by Gurney in this edition of the Journal of Small Animal Practice directs the interested reader to the BSAVA Manual of Canine and Feline Anaesthesia and Analgesia 2nd edition to learn more about local anaesthetic nerve blocks, and this is certainly a good starting point for those keen to advance their knowledge in this area. The question may be asked then, if local anaesthetics are the ‘perfect’ analgesics, why are they not more extensively used in veterinary practice? There are probably several potential reasons, but, at the forefront, the two likeliest are lack of training in regional analgesic techniques (both at an undergraduate and postgraduate level), and also the relative safety of current anaesthetic techniques in small animal patients. We only have to look to our colleagues in large animal practice who make extensive use of ‘local anaesthetic blocks’ on a daily basis largely because of the infeasibility of general anaesthesia for farm animals on an economic front, but also related to the greater risk of such a procedure in larger animals to appreciate that these techniques are the ultimate analgesic modality when the veterinarian is ‘forced’ to use them. The fact that general anaesthesia is now relatively ‘safe’ for most small animal patients means that due consideration is often not given to applying local anaesthetic techniques in conjunction with the anaesthetic. If we compare what we are doing with what occurs in human anaesthesia, one of the major differences is that regional anaesthetic techniques are administered almost ubiquitously to patients undergoing surgical procedures even if they are having a ‘full’ general anaesthetic. Not only will this allow anaesthesia to be kept ‘light’ during the surgery (and, therefore, lessen the cardiopulmonary depression that occurs with anaesthetic agents), but it will also dramatically improve post-operative analgesia. Perhaps if our patients were able to verbalise their discomfort post-operatively, the veterinary profession might be quicker to adopt local anaesthetic techniques as part of a general anaesthetic protocol! However, looking back at the previously mentioned studies from the 1990s on analgesic usage, we are obviously doing much better across the board. But does this mean we can pat ourselves on the back and say we are now essentially ‘on top’ of the problem of acute pain in small animals? There are probably still a number of areas where we can (and should) improve. One that certainly requires attention is that of pain recognition; it is of little value to have a relatively large armamentarium of analgesic drugs available if those animals that would benefit from their administration are not appropriately identified. Although we now have one validated acute pain scoring system for dogs (Glasgow Composite Pain Measure Scale), this does not appear to have been widely adopted (particularly in North America) and people continue to use poorly or non-validated systems and base their analgesia prescribing potentially inappropriately on these. In addition, while most of us would accept that detection of acute pain in dogs can sometimes be challenging, there is general consensus that cats are even more adept at hiding any outward signs of discomfort, and close observation is certainly required to detect the (usually) subtle indications that all is not well. Although a number of groups are moving forward in correlating behavioural indicators with pain in cats, to date we have no validated pain scoring system for this group of patients. When we consider rabbits and other ‘small furries’, we are, unfortunately, even further behind. So, how do we go about improving things? Relatively recently, the World Small Animal Veterinary Association (WSAVA) has established a ‘Global Pain Council’. This panel is made up of experts in the field of analgesia, and has identified as its mission statement “To raise global awareness and provide a call to action based upon the understanding that all animals are sentient and, therefore, feel pain and suffer from it”. The initial goal of this organisation is to produce a “Global Pain Treatise”, providing guidelines in both recognition and management of pain (acute and chronic) in dogs and cats, which will be used as a comprehensive resource for daily use by veterinarians. In addition, the pain management needs of different locations around the world (in terms of availability of drugs and equipment) will be investigated as the basis for instituting appropriate continuing education programmes throughout those areas. The final Treatise is due to be presented at WSAVA in New Zealand in 2013. The ultimate vision of the Pain Council is to achieve “An empowered, motivated and globally unified veterinary profession that effectively recognizes and minimizes pain prevalence and impact”. On behalf of all of our patients, we can only wish them every success with this venture. The author would like to thank Professor Karol Mathews, Chair of the WSAVA Global Pain Council, for her assistance with the preparation of this editorial. Derek Flaherty is Senior Lecturer and Head of the Anaesthesia Service in the School of Veterinary Medicine at the University of Glasgow. He holds the RCVS Diploma in Veterinary Anaesthesia and the Diploma of the European College of Veterinary Anaesthesia and Analgesia, and is both an RCVS and European recognised Specialist in the subject. Derek is Associate Editor (Anaesthesia) for the Journal of Small Animal Practice.

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