April has for me the best celebration of the year, Easter.  A “movable feast” as of course the date varies between March 21st and April 25th.  I like a bit of unpredictability but wouldn’t it be easier if the same date was set every year, like Christmas Day?  We could put the clocks forward on Good Friday and enjoy the extra daylight over the holidays.  What do you think? My secular thoughts about religious festivals aside and as uplifting and happy as Easter is, it strikes me that it has a darker element.  I refer to Christ’s crucifixion and the pain he must have suffered along with countless others condemned to the same fate.  So I wanted to write about the alleviation of pain and how to recognise it in animals, who of course, cannot speak.  I am sure my human medical colleagues face similar challenges with patients who cannot communicate verbally.

Different species respond very differently to pain, mainly due to evolutionary adaptations that help survival.  Frequently, when animals are victims of road traffic accidents, they are able to run away from the scene despite serious injuries.  It’s thought this response helps wild animals escape a predatory attack, the pain delayed for a period of minutes or hours to allow the victim time to reach safety.  I have personal experience of this after a surfing accident a long way from shore when I broke two ribs and didn’t feel any pain for an hour or so.  At least it gave me time to get back to the beach and remove my new wet suit that I thought would be cut off me at Truro hospital!  

So our patients fall into two broad categories; those that come in already painful and those that face a potentially painful elective procedure, for example, neutering or removal of lumps and bumps.  Unless you are bringing your pet in for a routine vaccination or check up, I take the view that all sick animals are in some degree of pain or discomfort, no matter how “trivial” the underlying problem might be.  Think about how badly your head or joints ache with a simple cold virus, not to mention the effects of Covid! 

This brings us to the question of how we detect and measure pain in animals.  There has been plenty of research trying to find objective markers for pain (ie blood tests for adrenaline etc, heart rate and blood pressure) but factors like stress and excitement affect the results.  Instead, we use behaviour to guide our assessment, as it clearly changes with the type and severity of the pain.  But there are problems here too, so let’s consider what happens when your dog has its annual vaccination, usually under the skin at the scruff of the neck.  Some will feel it and maybe just flinch, many can be distracted from reacting at all with food but some react violently and occasionally, aggressively.  Given that the “stimulus” is the same, this illustrates the variation in response.  Also consider what sometimes happens when I try to give a kennel cough vaccine up your dog’s nose!  This really is not painful and yet it often evokes extreme reactions.  So clearly behavioural responses are not influenced only by the degree of pain, individual stress and fear play an important role.

How does all this affect our efforts to assess pain and so treat it effectively?  Obviously it doesn’t make it any easier but vets and nurses are now much better at recognising the more subtle signs of pain in dogs and cats.  Like many animals, dogs and cats become quiet and depressed with chronic, unremitting pain and this used to be interpreted as peaceful resting.  We now know these animals need more analgesia and we are quick to supply it.  Quite often, of course, the signs are not subtle at all, especially if the pain is sudden and sharp.  Most vets develop quick avoidance reactions but the real trick is to read your patient, be gentle and provide good pain relief as soon as possible.  For those about to undergo an operation, we give pain relief before the procedure as we now know this reduces post-operative discomfort.

The sensation of pain is also not a single entity and all of us appreciate the difference between hitting a thumb with a hammer and the nagging pain of chronic arthritis.  This is not just a matter of degree as there are very different nerves involved, sudden sharp pain being transmitted by “A” fibres and dull, chronic pain by “C” fibres. The process of detecting pain by nerve endings and transmitting signals to the brain via the spinal cord is called “nociception”.  These signals undergo complex modification on their journey up the spine that can result in either amplification or suppression.  We obviously want to suppress pain in our patients and the morphine-based analgesics are now widely used in almost all situations, alongside non-steroidal anti-inflammatories and paracetamol, all of which can be given in combination and intravenously for rapid effect.  The most difficult pain to control is “neuropathic” pain, where there is no detectable tissue damage.  This is well known in human medicine and we recognise it increasingly in animals. Luckily there are new ways of controlling this sort of pain, one of which is an antibody to a neuro- transmitter involved in nociception.  

Pain relief is an essential part of medicine.  Palliation is now a speciality subject in human medicine and it needs to be given similar recognition in the veterinary profession.  I am glad to say we are getting there.