ABSTRACT: II is now widely accepted that animals feel pain. Providing analgesia is, therefore, an integral part of animal welfare. This article summarises the need for proactive pain control, outlining interventions and pharmacological treatments we can consider and explains how pain can be assessed and controlled in practice.
The word analgesia literally means total absence of pain. However, the analgesics routinely used do not completely abolish the sensation of pain but modulate and decrease its perception. Local anaesthetics are the only drugs able to suppress the sensation of pain.
The nature of pain
To understand how pain is perceived and, therefore, how it can be treated, knowledge of the pathophysiology of pain is fundamental (Figure 1). As a consequence of the complexity of pain pathophysiology, it is understandable how a single analgesic drug cannot be expected to effectively control pain in every subject.
Figure 1: The pain pathway – nociception
Pain varies between species and within the same species – it might vary depending upon breed, age and sex. Furthermore, the response to analgesics might be different owing, for example, to the corresponding number, distribution and morphology of specific receptors (for instance, opioid receptors in the dog and cat).
The administration of two or more analgesics acting at different levels of the pain pathway might lead to a better control of the nociceptive stimulus. This technique of multi-modal analgesia might also allow a reduction in the dose of each individual drug, lowering the risk of drug related side-effects. Figure 2 details the nociceptive pathway and the multi analgesic approach.
Figure 2: The nociceptive pathway and multi
Initially pain is beneficial and necessary for survival, by limiting the extent of injury, forcing rest and teaching the animal to avoid similar noxious stimuli in the future. Absence of pain perception is a catastrophic pathology, termed congenital analgesia. However, if acute pain is not controlled adequately, it becomes a negative experience and may induce diseases associated with chronic pain. Persistent pain results in a prolonged stress response precipitating increased circulating cortisol and catecholamines, leading to:
• tachycardia
• vasoconstriction
• hypertension
• increasing myocardial oxygen consumption
• decreased gastric motility
• delayed healing
• sleep deprivation
• hypoventilation and increased risk of lung infection
• catabolism leading to muscle atrophy
• prolonged immobility and functional recovery.
This up-regulation of inflammatory mediators firstly leads to sensitisation of peripheral nociceptors and then leads to changes in the spinal cord, termed central sensitisation.
Primary hyperalgesia is a nociceptive stimulus perceived as more painful than normal. Secondary hyperalgesia is the perception of pain in areas not directly affected by the trauma. This is caused by central sensitisation and further recruitment of nociceptors.
The end stage of this pathological process is allodynia, whereby a stimulus that would not normally cause pain is perceived as painful. If acute pain persists, self-mutilation can occur or may become chronic pain, in which pain is perceived despite healing of the injured tissue.
Nurses and pain assessment
Pain, distress and suffering are considerably unpleasant, aversive and disagreeable mental and emotional sensations. As veterinary professionals, we aspire to avoid these states. Therefore, providing analgesia is not just a medical, but also an ethical, demand. Unfortunately, assessing pain in animal is not so straightforward. When in doubt, it is reasonable to use a degree of anthropomorphism, anticipating that painful situations for people are also likely to be painful to animals.
For surgical patients, pre-emptive administration of analgesics is an important component of intra-operative cardiovascular stability, reduced postoperative analgesic requirement, early and comfortable recovery and, generally, a more successful outcome.
In human medicine, local and regional techniques decreased the consumption of postoperative analgesics, and decrease hospitalisation time compared to purely systemic administration of analgesics. Using these techniques the postoperative consumption of opioids may also be significantly reduced in animals, causing less sedation and cardiovascular depression, thereby promoting a rapid comfortable recovery.
During the recovery period, each patient should be assessed individually and analgesics administered accordingly. Quantifying pain in animals is challenging. Like infants, animals cannot communicate the amount of pain perceived or if the analgesic administered decreases the pain sensation. Therefore, we must rely on behavioural and occasionally physiological responses.
Effective pain management requires stringent observational and assessment skills. The decision-making process can be facilitated using pain scoring systems. For dogs, different pain-scoring systems have been published but only the Short Form – Glasgow Composite Pain Scale (Figure 3) has been validated.1
Figure 3: Short Form – Glasgow Composite Pain Scale
Currently, no pain scale has been validated in cats. In our practice, a modified ‘4avet’ scoring system is routinely used (Figure 4). Nevertheless, when choosing a pain-scoring system, it is important to select one that fits the individual practice, to be easily incorporated into on-going patient assessment, treatment and reassessment protocols, and will be initiated easily and consistently by staff.
Figure 4: Modified 4avet' Feline Pain-scoring Chart
In our practice, postoperative analgesia is generally assessed every two hours for the first 24 hours, and subsequently every four hours using the aforementioned scoring systems (Figures 3 & 4). Analgesics are prescribed to be administered accordingly.
Nurses are fundamental in this process and communicate their assessment to the anaesthetist or clinician responsible for the care of that animal. In some situations, however, such as in aggressive animals, the use of these scales m
ay be impractical, so analgesics are administered at time-based intervals.
Regular feedback and interrogation of pain control measures are invaluable for driving flexible and appropriate analgesia. Full appraisal of the analgesic plan by assessing the trend of scores obtained will enable a revision of treatments and adjustment according to the animals needs.
It is important to stress that the administration of drugs based on a pain- scoring system does not imply that the drugs are administered when the animal is experiencing a considerable amount of pain. Postoperative analgesic requirements are highly variable. Routine administration of opioids at regular intervals – for example, morphine every four hours or buprenorphine every six or eight hours – can result in a relative overdose in some patients, and breakthrough pain in others.
Wider considerations
A successful pain management system is of benefit primarily for the animal – improving its quality of life and reducing the incidence of complications. Appropriate analgesia also enhances the human-animal bond, increases staff safety, morale, pride, job satisfaction in a less stressful environment and effectively fulfils the responsibility to relieve animal suffering.
Other interventions that should be considered to reduce pain include:
• supportive dressings
• avoiding unnecessary drains and catheters
• tension-free sutures and hot or cold
• compresses to aid tissue healing and
• reduce inflammation
• life style changes, such as weight loss and controlled exercise
• raised food and water
• soft bedding
• non-slip flooring
• easy access to toilet and warm up prior to exercise
• positive, consistent nurse-to-patient interaction to improve demeanour and promote rest
• minimised anxiety through gentle respectful restraint and handling
• provide calm visual and auditory stimulation
• provide shelter and a safe hiding place
• minimise hospitalisation duration
• provide nutrition or support feeding until complete recovery
• consider nutraceuticals, such as glucosamine and chondroitin to decrease joint inflammation and to assist cartilage repair.
Home care should continue, with client counselling on the signs and significance of post-discharge pain, so proactive pain control can also be continued after hospital discharge.
In addition, behavioural signs of pain may be masked while patients are hospitalised and these may only become evident once animals are home. Client education also enhances their perception of a practice that is committed to appropriate and pro-active pain relief.
Author
Anya Owen Dip AVN HE Dip CVN (SA) RVN
Anya is the head medicine nurse working at Dick White Referrals veterinary specialist centre in Suffolk, where she has worked for the last five years. With a particular interest in cardiology, oncology and anaesthesia, she enjoys all aspects of referral nursing, striving to provide the highest level of nursing care.
To cite this article use either
DOI: 10.1111/j.2045-0648.2011.00120.x or Veterinary Nursing Journal Vol 26 pp 432-434
Reference
1. HUNT. J. [2011] Recognition and Quantification of Pain in Small Animals – an introduction Association of Veterinary Anaesthetists www.ava.eu.com/articles/1899-recognition-and- quantification-of-pain-in-small-animals- %E2%80%93-an-introduction
Additional references
American Animal Hospital Association 12007) AAHA/AAFP Pain Management Guidelines lor Dogs and Cats Journal of American Animal Hospital Association 43 235-248 www aahanet.org/Public Documenls/PainManagementGuidelines.pdf
BENSON. G J [2000] Anaesthesis and Analgesia Physiological Effects of Pharmacological Agents University of Illinois www med.yale.edu/yarc/vcs/anaesthesiaeffect.htm
BR0DBELT, D C and GIRLING. S. J. 120081 Anaesthesia and Analgesia Eds Lane, D.. Cooper.
B & Turner. L BSAVA Textbook of Veterinary Nursing 4th edition British Small Animal Veterinary Association. Gloucester
CHURCH. J S 120001 Understanding Pain and its Relevance to Animals
MACKAY. S 120061 Pam relief without the tears' Veterinary Review
GLEED. R. and SEYMOUR, C. (Eds) [1991] BSAVA Manual of Small Animal Anaesthesia and Analgesia BSAVA. Cheltenham
THOMPSON. D 120041 The Pam Process Veterinary Anaesthesia Support Group www vasg.org/The_ Pain _Process.htm
WHITING. S.. SMEETON, 0 , GODDARD, L and EWART, J 120071 Pre- and postoperative nursing lEdsI Martin. C & Masters. J in Textbook of Veterinary Surgical Nursing Elsevier Butterworth Hememann
WOOD. S [2008] Anatomy and Physiology of Pam' Nursing Times www.nursingtimes.net/nursing-practice-clinical- research/anatomy-and-physiology.htm
• VOL 26 • December 2011 • Veterinary Nursing Journal