I had a really fascinating lecture on post-operative pain today.
'There's a debate about whether animals feel pain?!' exclaimed my friend when I mentioned an earlier pain lecture. My friend is studying art and grew up with pet cats. She was shocked and appalled to hear that anyone would question whether animals feel pain because it is so obvious to her that they can. She laughed as I tried to explain the fact that, yes, quite a lot of very educated people have argued that animals don't feel pain.
There was also time - the 1980s - when American medical doctors didn't believe that baby humans felt pain and performed open heart surgery on babies without anaesthesia or analgesia (pain medication). Those babies grew up to have problems later in life and those doctors were sued by very angry mothers. The babies couldn't tell the doctors that the surgery hurt because they were too young to know how to talk, and the doctors didn't notice behaviours the babies performed that would indicate that they were in pain.
Now, lets go back in history prior to that strange time in the 1980s to the 1800s.
Prior to the invention of anaesthesia, surgery was performed. One woman wrote about her mastectomy, performed in 1811 without any anaesthesia, and she said, as you might guess, that it really hurt.
I should mention that there was a time just after this when really cruel vivisection became trendy and rich white dudes started nailing their dogs to their tables and cutting them open while they were awake. The world gained knowledge about anatomy, but anaesthesia was being invented at the time and it would have been nicer for those dogs if they had been given some anaesthesia.*
In the 1840s, anaesthesia started being used for surgery.
When we Americans tell dark jokes about 'doing Civil War medicine' its actually incorrect/ironic because the time period during the American Civil War was the first time in history that 'best practices' like anaesthesia began.
In North America, Ether was the anaesthetic of choice. In Britain Chloroform was the most popular.
Chloroform killed quite a few young people (they were probably anxious about their surgeries and had high heart rates and high heart rate and chloroform don't mix well). This lead to laws that only a Doctor could perform anaesthesia in the UK. The Ether used in America only killed old people and was safer, so in America, nurses were allowed to anaesthetize. This is still true, even in veterinary medicine. In the UK only Veterinarians are allowed to anaesthetize animal patients. In the USA Licensed Veterinary Technicians can anaesthetize, although a supervising Veterinarian should be present.
Morphine, Lidocaine and Ketamine were all invented pretty early in modern history. These are still the most important drugs to manage post-operative pain in veterinary medicine, but they are used in different ways now.
For a while veterinary surgery was performed on awake animals. This is kind of where this story ends for farm animals who still routinely have surgeries without anaesthesia or analgesia.
Later, drugs were given to make dogs immobile so surgery was easier for the veterinarian (and for the poor assistants who had been holding down awake animals during surgery). Other drugs could be given to reverse the effect of the immobilizing drugs and wake up the dog. This was helpful for the people performing the surgery, but didn't really help the dog.
There is a natural pain response that is part of our bodies which helps us survive. Part of this is the stress response involving adrenaline. Part of this involves endogenous opiods (natural opiods in the brain that help stop you from feeling pain). This natural pain response is what gives soldiers the ability to keep fighting on the battlefield even if they have been badly wounded. It helps animals survive in the wild after being attacked by predators.
Unfortunately, when veterinarians were first using opiods to immobilize their canine patients during surgery, they would use an opiod-reversing medication to wake up the dog after surgery. This medication reversed natural endogenous opiods too. If the endogenous opiods are stopped by a reversal drug then the animal will not have the natural response to manage pain and the dog will likely feel more pain than if the surgery had been performed while the dog was awake.
(I'm writing this as if we've totally left this practice in the past and all veterinarians in the world are using better drug protocols now, but unfortunately that is not entirely true.)
Currently, it is best practice to use a variety of different types of analgesics and anaesthetics to manage pain in a multi-modal way.
Here is the most important word that I have learned from my biology of suffering pain lectures: SENSITIZATION
If you are a veterinarian or animal researcher I recommend reading about sensitization because it is really fascinating. I might write another post about the bio-mechanics of this process, but it is neuroscience heavy and I might lose some people if I do that now.
Very, very basically, sensitization is this crazy thing that happens in the body that makes pain more painful over time. And it can start as soon as you start to cut a patient.
Wound -> nerve signalling & a the release of a bunch of chemicals -> pain + stress response
The 'nerve signalling & release of a bunch of chemicals' part repeats.
The body becomes more sensitive. The chemicals at the area of the wound make the skin look red and feel hot to the touch and make the areas near the wound more sensitive.
This can cause allodynia - which is when a gentle touch feels painful. Sensitization can cause chronic pain.
This processing is really weird and magical and problematic for veterinarians because it happens even when patients are anaesthetized. It can cause patients to feel more pain later e.g. after the dog has had surgery and gone home.
Luckily, sensitization can be prevented with appropriate pre-surgical analgesia and/or local anaesthesic blocks like local nerve blocks.
In human medicine, women who were given general anaesthesia to immobilize them for C-section surgeries and muscle relaxants to make the surgery easier for the surgeon, sometimes reported pain and/or memories of the surgical procedure after they had gone home from hospital. These women had no clinical signs of waking up during the C-section (no elevated heart rate, etc.).
Women who were given epidurals - local anaesthetic nerve blocks - did not have this problem. The local nerve block stops central nervous system sensitization.
Pre-operative pain medication should be given to stop local sensitization and the build-up of the inflammatory response. For example, an NSAID could be given prior to surgery and the timing should be such that the NSAID is acting fully on the tissue being cut as the incision is first made.
My lecturer was a really big fan of 'splash-blocks' (Shout out to MO if you're reading this!) which is when a local anaesthetic like lidocaine is sprayed or squirted into the surgical site as the surgery is performed. He was also a big fan of nerve blocks and even nerve catheters which deliver local anaesthetic, again usually lidocaine, directly into the nerve near the surgical site. Finally, it is extremely important to give post-operative pain medication. Our lecturer recommended that post-operative pain medication be given until the wound is healed (5-30 days!) The reason it is so important to give post-op analgesia is that sensitization can start as soon as the pain medication given near the time of surgery wears off.
Sensitization can lead to really bad chronic pain.
Instead of acting like the doctors in the 1980s who did surgery on babies without pain management, we should give patients the benefit of the doubt and try to manage pain appropriately even if when can't verbally tell us how they feel.
*At least one of these dudes was yelled at by his wife for nailing their dog to their table and cutting the dog up, but he was all like, 'Shut up, I do what I want!' because he thought women were inferior to men just like dogs were inferior to men. Unfortunately, this dude was Descartes and he had a huge role in shaping modern Western thought.
