Most people would raise an eyebrow at having surgery without any post-op pain relief, even a paracetamol! Yet it’s not that uncommon for people to question whether cats need pain relief after a surgery, or if they even feel pain during surgery. Is this true? Do cats need pain relief during and after a surgery? Do they feel pain like we do?
What is Pain?
Before we get to cats, it’s worth discussing what pain actually is. Everyone knows the feeling of various kinds of pain, but what is the science behind pain? The perception of pain can be split into four steps: transduction; transmission; modulation; perception. It is a very complex system involving sensory nerves all over the body and various parts of the brain. We do not fully understand how it works, but here is what we do know.
Transduction – detecting damage:
“Nociception” is the activation of nerves that detect damaging stimuli on the body. There are three main kinds of stimuli that can activate this pathway. These are thermal (excessive heat or cold), mechanical (pressure, stretch, cuts etc.) and chemical (changes in acidity, irritant chemicals, capsaicin in chili peppers, etc.). When tissue is damaged by one of these stimuli, it releases chemicals (such as histamine, cytokines, or globulins) into the area. These chemicals activate the nerve endings of sensory neurones – these nerves are called nociceptors. Different types of nociceptors are activated by different stimuli. These nerves are located all over the body: skin; joints; eyes; organs; bones; muscles. Strangely, we have not identified nociceptors in the central nervous system (brain and spinal cord), lungs, joint cartilage, and pericardium (the sac that surrounds the heart).
Interestingly, there are also local pathways that are activated before nociceptive signals reach the brain, termed stretch reflexes. These reflexes are activated when nociceptors detect a stimulus and rapidly transmit the signal to the muscles, causing a motor response (generally activating flexor muscles and contracting extensor muscles). The most well-known example is the withdrawal reflex of the hand that follows touching a hot stove – the body wants to withdraw the hand from the potentially harmful stimuli as rapidly as possible, and the signal travelling to the brain and back would be slower. The tapping of a knee with a small hammer by a doctor tests another reflex, the knee stretch reflex.
Transmission – sending the signal:
Once a nociceptor nerve has been activated, the signal travels from the peripheries to the spinal cord, and up to the brain. Nerves can transmit a signal quickly for acute (sudden) nociception, or slowly for more long-term pain. This signal can be blocked via damage to nerves (such as in paraplegic patients) or with certain drugs. Once in the brain, the signal spreads to various areas including the thalamus, amygdala, hypothalamus, basal ganglia and cortex.
Modulation and Perception – feeling it:
Before perception as pain, the spinal cord and brain may modulate the nociceptive signal, often by releasing analgesic (pain relieving) chemicals such as opioids. This may result in the perceived pain being lessened or even completely prevented. This is partly why the same injury can be more or less painful to different people. Other factors, such as personality, experience, gender, and even economic factors can affect the perception or tolerance for pain. Chronic pain can also be lessened in the same way. Pain can also be heightened by the ‘wind-up’ effect, where repeated nociception leads to an increased pain perception, meaning sensitivity increases and even stimuli normally not activating nociceptors will do so, leading to further pain.
Alongside modulation, the nociceptive signal is processed by the brain and may be perceived consciously as pain. It is important to note that not all nociceptive signals are perceived as pain, and pain can be experienced without any actual nociception (such as psychological pain). The signal sent from nerves to the brain, or how the brain perceives the signal, is not always precise – this is why some sources of pain can be felt in multiple areas (such as diffuse lower back pain after a slipped disc) or even distant to the actual nociception. This is termed ‘referred pain’, and can be one reason why doctors and vets may struggle to identify the actual source of pain, or even lead the patient to believe the pain is ‘in their head’.
Sources of Nociception and Pain During and After Surgery
To understand if a cat feels pain during and after surgery, we should first identify the possible sources of pain, as well as the kind of stimulus it is. The causes of pain are listed in a rough order they may occur in a routine procedure. The list is not exhaustive, and will vary between patients and operations.
Sources:
- Intravenous catheter placement. An IV catheter is used to give intravenous medications and fluids to an animal. Placement involves inserting a needle through the skin into a vein. This causes mechanical damage to the area.
- Subcutaneous or intramuscular injections. Needles are inserted into an area to inject medication. This causes mechanical damage. Some drugs are irritants, which causes chemical damage. Subjectively, some intramuscular injections appear to be more painful than subcutaneous injections.
- Shaving. Animals must be shaved prior to surgery. This can lead to clipper rash, which is a combination of mechanical and thermal damage.
- Endotracheal tube placement. To provide oxygen and maintain anaesthetic via inhaled gases, an ET tube is placed in the trachea. This can cause irritation of the trachea, leading to mechanical damage.
- Manipulation of the body. While under a general anaesthetic, an animal must be placed in a certain position. Particularly in older animals or those with joint or muscle disease, improper manipulation, lack of padding, or prolonged awkward positioning can lead to mechanical damage.
- Cutting tissue. Surgeons typically cut using sharp scalpels to minimise excessive damage, but there will still be mechanical damage to the skin, subcutaneous fat, muscle, organs and bones that are cut. If an electric scalpel or thermocautery is used, thermal damage may occur too.
- Manipulation of organs. To perform surgery, organs, such as the uterus and ovaries during a spay procedure, must be manipulated. If not done gently, this can cause stretch or bruising, leading to mechanical damage.
- Temperature. During and after surgery, an animal’s temperature must be closely monitored. Severe thermal damage can occur – for example, burns if heating elements are used incorrectly. Feeling too hot or cold can still lead to discomfort and emotional pain, even if true nociception is not activated at less severe temperatures.
- Post-operative pain. Well after the surgery is over, the tissue manipulated, cut into, injected or otherwise traumatised will continue to release inflammatory chemicals and send nociceptive signals to the brain, unless otherwise mitigated. These can be mechanical or chemical. Complications, such as post-operative infections, can worsen this pain.
- Emotional pain. Although not a direct activation of nociceptors, emotional pain as a result of physical pain, temperature discomfort, noise, smell, being away from home, etc. must all be addressed.
By causing discomfort and psychological distress, pain is a welfare issue. On top of this, pain can physiologically affect the body in a variety of ways, which can directly slow down the healing process, reduce appetite and thus the energy necessary for healing, and affect the immune system leaving an animal vulnerable to infection. This is why we must always strive to reduce pain in animals as much as possible.
Do Cats Feel Pain After Surgery Like We Do?
With all the physiological understanding of how nociception and pain works in many animals, including cats, and some idea of the possible causes of pain during surgery, can we determine if cats feel pain like we do during and after surgery. While we cannot answer if they feel pain in exactly the same way (remember pain is subjective between individuals, and animals may process pain differently due to their different brain capacities), we are certain that cats will feel similar kinds of pain to a human undergoing surgery.
Vets can determine pain in a cat through various means. Physiological changes can be used as a guide, such an increased breathing and heart rate, increased temperature, lack of appetite, and so on. However, many of these changes can be seen in other states, such as stress and disease, so cannot be used alone.
Instead, many vets will recommend pain scoring cats
This is usually done visually by assessing a cat’s behaviour. For example, a cat in pain will generally not want to move, may be hunched up, have their eyes semi-closed and ears pulled back, and have low whiskers. They may be aloof, fearful or aggressive when interacted with. On the contrary, a comfortable cat will be more active and willing to interact with a person, have wide eyes and upright ears and whiskers. A comfy cat will be happy having the surgical site touched, while a painful cat will resent this. Comfortable cats will often sleep in their kennel, while painful cats will remain awake. To aid assessment, there are simple tools that can be followed to assess pain in cats – these are something owners can learn to use as well to assess pain at home. The tools include the Feline Grimace Scale, and the Glasgow Composite Measure Pain Scale. If a cat scores above a certain value, they are in unacceptable pain and interventions should be made. Repeated scoring should be made to determine if pain is reducing.
There are limitations to pain scoring cats, however. It has been noted that individual people may assess pain differently, notably those without training and males tend to score pain lower than people with training and females. The score can also be limited in cats with behavioural issues, such as extremely fearful or feral cats that would show similar behaviours as a cat in pain. Certain drugs, particularly ketamine and high doses of opioids, can also cause abnormal behaviour that may either mask or be misinterpreted as pain.
How to Prevent and Treat Pain Around Surgery
So we know that cats indeed do feel pain during surgery, and for reasons we’ve discussed above it is important that vets minimise this as much as possible. Here are some of the ways this can be done.
Preventing pain is always better than managing it after the fact, so vets will often use analgesic drugs as part of sedation protocols. These may include opioids like methadone or buprenorphine, a2 agonists like medetomidine, and ketamine. Pain relief can be given as a single injection or a constant infusion via an IV catheter. Pain can also be prevented with local anaesthetic drugs that block the pain signal forming – these can be injected into the site (like the skin or organs), splashed over wounds, or even applied as a numbing cream prior to injections or catheter placements. Cats in particular usually receive local anaesthetic spray into their airways prior to ET tube placement. Avoiding certain drugs that cause more severe chemical damage can also minimise pain, such as intramuscular use of ketamine.
During a surgery, a vet can minimise pain by utilising proper equipment and techniques. Ensuring sterility prevents harmful bacteria colonising a wound and resulting in post-op infections and pain. Sharp scalpels and atraumatic forceps minimise damage and thus pain when cutting through skin, while gently handling the organs prevents a stretch response. The nurse can also minimise pain by ensuring the cat’s temperature is within the normal limit, minimise manipulation of the cat while under anaesthetic, and monitor for signs of nociception (remember there cannot be pain if a patient is fully anaesthetised).
Post-operatively, a successful surgery will mean the cat wakes up comfortable with no signs of pain. While still in hospital, nursing care can minimise emotional pain – this may include warming the cat, providing food and water, ensuring they can toilet comfortably and cleanly, their wound is not touched by humans or the cat himself, and keeping the cat isolated from dogs, loud noises or other distressing things. Continuing pain relief in hospital and at home, with opioid or non-steroidal drugs, will help keep the cat comfy, and TLC from the owner will provide for their emotional wellbeing.
Should there be any concern the cat is showing signs of pain, an owner should alert their vet straight away.
Further Reading
Physiology, Pain – StatPearls – NCBI Bookshelf (nih.gov)
The Anatomy and Physiology of Pain – Pain and Disability – NCBI Bookshelf (nih.gov)
Pain Mechanisms – Physiopedia (physio-pedia.com)
Postoperative pain—from mechanisms to treatment – PMC (nih.gov)
Pain management in cats—past, present and future. Part 1. The cat is unique – PMC (nih.gov)
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