7⃣ ENTENDENDO A FISIOPATOLOGIA DA DOR | Anestesia é o Básico #7

'Pain is inevitable. Suffering is optional. ' 'Well, every one can master a grief, but he that has it.

' 'We feel pain, but not painlessness. ' 'A broken heart hurts worse than these broken bones. ' 'Love is a pain that rages without hurting.

' All these phrases share a common feeling: pain. And that's what we are going to see in today's video lesson. Bring it on!

Pathophysiology of Pain What's up NAVE crew! In today's Anaesthesia Unravelled video lesson we'll be talking about pain, which is one of our most basic feelings. Anaesthesia was created in order to prevent pain, we even talked about it in the first video lesson, 'The history of anaesthesia' I suggest that those who still haven't watched it go check it out.

Portraying pain is incredibly complicated. This fellow here became a meme related to pain out of nowhere, the poor man wasn't even feeling any pain at the time. What can we say about these two people?

They are of the same species, in fact, our own, but we know that Eastern people, historically, demonstate less pain than Latinos. I, that am half Bahian - half Italian, am a calm person, very chill, I don't usually express pain at all, it's something I deal well with. Just don't show me a needle.

. . *loud swearing in portuguese* Now, what can we say about these two breeds?

One was created to be a guard dog, while the other, to be pretty. Will they feel pain differently or only express it differently? What if we compare a dog and a cat?

Or a cat and a horse? Or a horse with a cow? Oh no, professor, bovines are impervious to pain.

You're kidding, right? That's makes absolutely no sense. The most important thing is that we understand what the expression of pain is for each species.

What about birds, reptiles? Oh, come on, reptiles? My friend, stop right there.

All animals feel pain, the problem is that we need to find a method to identify it. Well, but before we discuss pain recognition, let's try to understand how it works. Pain doesn't exist specifically to make the individual suffer, it has the purpose of protection.

If feel pain, I will obviously avoid an action that can injure me further. Another interesting feature of pain is social organization, which is important historically, and finally, it's a way of learning, who here never stuck a finger in a wall socket, or on the fire, as a child? *singing in portuguese* Ouch!

So, it's better for us to understand that we have physiological pain and pathological pain. The anatomy and physiology of pain Regarding the anatomy and physiology of pain, we have to remember three fibers: the Abeta fibers are responsible for transmitting the feeling of touch and pressure from the periphery to the central nervous system. The Adelta and C fibers, on the other hand, are responsible for taking the harmful stimuli from the periphery to the central nervous system.

That means that, on one side, there's a fiber that transmits all unharmful feelings, and on the other side there are fibers that transmit painful sensation. Why is any of that important? As we can see on the picture, the stimuli from the periphery follows a path to the brain.

The first step is the transduction, where there's the transformation of the mechanical, thermal and chemical stimuli to an electrical impulse. After that, the afferent fibers take this electrical impulse to the spinal cord. This is the transmission step.

In the spinal cord, there's the modulation step, where the impulse can be exacerbated or inhibited, depending on the situation, and finally, we have the perception, that is the moment the stimulus arrives at the brain. Then, depending on the stimulus, this can turn out to be just an innocuous feeling, as touch, or a harmful stimulus, like a cut or strong impact. Oh my god.

We can see on this picture that, on one side, the Abeta fibers, that have mechanoreceptors, take the innocuous sensation to the brain, and on the other side, the Adelta and C fibers, that have nociceptors, that lead to a feeling of pain. Now, why is this important? Because there are some concepts related to pain and these fibers that we really need to understand in order to know if one thing or the other is taking place.

So, one very interesting example we like to use is that on an ingrown toenail. Let's say that around an ingrown toenail there was tissue injury that lead to an inflammatory response. Then, all those substances related to inflammation, prostaglandins, histamine, and else, will sensitize that area, causing the fibers to suddenly lower their excitability threshold.

Therefore, a stimulus that had to be slightly stronger in order to trigger the process of taking the impulse to the brain, becomes less intense after inflamation. This is called hyperalgesia. There's primary hyperalgesia, which occurs where the injury takes place, and the secondary hyperalgesia, that is in the injury's proximity.

The problem is that the process falls into a loop, the more it hurts, the more painful it becomes, leading to the increasing production and release of inflammation by-products, and this pain escalates. At a given moment, the Abeta fibers, that are usually not responsible for taking the pain stimulus to the CNS, start to carry out this role, and this is called allodynia, a sensation that wasn't considered painful becomes pain. why is it so important to understand all that?

Because we need to quench pain before it happens or right at the beginning. With that we can avoiding hyperalgesia and allodynia. It's as that famous saying: 'Better safe than sorry.

' If we focus on post-surgical pain, studies have been showing that if we can successfully block pain in the first 24 to 36 hours, that patient will practically feel no more pain afterwards. That obviously depends a lot on the surgical procedure. Now, if it is not properly treated, pain can persist for a long time.

Pain classification The pain can be classified by the duration. In this case, we have acute pain, which usually lasts a maximum of seven days, it's secondary to acute processes, as surgery, or a blow, and it is localized and very responsive to analgesic treatments. As I mentioned, if the pain treatment isn't good, it ends up persisting, and we usually call that subacute pain, even though textbooks do not use this term.

They're, generally, painful processes that last up for 15 to 20 days, and end up showing characteristics of hyperalgesia and allodynia. Now, chronic pain is very complicated, it is usually related to pain longer than three months, is diffuse and unspecific, we have difficulty identifying it, and the treatment is not easy. The drugs we use for acute pain don't work as well for chronic pain.

It usually occurs in oncologic patients, those with osteoarthritis or nerve damage. The other way of categorizing pain is using its location, whether its origin is somatic or visceral. Somatic pain is usually related to pain on the skin's surface, bones and the extremities in general.

It is localized and, therefore, easier to treat. Visceral pain involves either chest, abdominal or even pelvic pain. It's usually diffuse, and that we are not able to pinpoint very well.

It's worth highlighting that somatic pain is easier to locate because 90% of the Adelta and C fibers are on the periphery, so they represent a small part of the dermatome. In the case of viscera, there are 10% of these fibers active, and because they are few, they need to innervate a rather large region, making difficult for us to pinpoint the specific location. At least, there's the neuropathic pain, that is usually related to amputations, chemotherapy or chemical nerve damage.

Neuropathic pain is complicated because it involves peripheral and central changes and it usually evolves to chronic pain. The feeling is related as burning, tingling, stings, pinpricks, and it is very difficult to treat. It all seems nice and easy in theory, but how do we actually recognize pain in an animal?

Pain recognition Up to the 17th century, if was common belief that animals felt no pain. Not today, right? It was a quite 'Cartesian' way of being.

So, that meant they could do anything on animals, cut them open even, for medical students to learn how the. . .

"human" body worked. It's kind of crazy because they used their findings in humans afterwards, but for them the animals felt no pain. In the early 20s, we had already started to have an evolutionary vision, that is, anthropomorphic.

As that goes, we try to understand the pain that the animal is feeling like it’s our own. I don’t honestly know if it's the same, but, as an anesthesiologist, I prefer to consider that, if that situation is painful for me, it will also be for the animal. So, when in doubt, it is interesting that we put ourselves in the patient's place.

Beyond that, we can also use some metrics to facilitate this process. There are some simple scales for pain assessment and others much more complex. But, independent of the scales, one thing I can say for sure is that the physiological parameters practically have no role in pain assessment.

It's much more behavioural. The first scale, the simplest of all, is the visual analog scale. It's very easy to use, because we just need to draw a 10 cm line on a piece of paper, where the zero corresponds to an animal without pain, whilst 10 is the worse pain possible, and then, the person who is evaluating makes a mark on the middle of the line, where they find it convenient.

We base ourselves on the theory that animals that have an increase over 30% on that scale need analgesic treatment. This scale can be used for any patient, it is very easy to do so, very simple and perhaps because of this simplicity, it may not portray very well what is happening. In order to reduce this bias, the University of Colorado developed two very neat scales, I like them a lot, for dogs and cats, as we can see in the pictures, that relate behaviour to the palpation of the painful region, and even body position.

It's worth remembering that these two scales, both the visual analog scale, that we call VAS, as these two scales from the University of Colorado, they focus on a clinical application, so we can examine the animal, choose an analgesic treatment according to the situation. It'll be different in experimental situations. We are going to need more sentitive scales, and, preferably, validated ones.

In that sense, for dogs we have the Glasgow scale and the simplified Glasgow, and for cats we have the Botucatu scale. They're good and even slightly complex, if we consider a clinical situation, it becomes a bit hard to use, but in an experiment, and scientific situation, they must be used. In horses we can highlight three current scales.

The first is the Bussières scale, that is more related to orthopedics situations. The second is the Suton scale, which is more related to abdominal pain and, more recent, we have the assessment of facial expression of Dalla Costa. This scale is very interesting because it assesses only the animal's facial expression.

It is worth mentioning that this study by Dalla Costa was made in animals subjected to orchiectomy. In ruminants the area it's still a bit underdeveloped. For ovines, there's the facial expression scale of McLennan, and for bovines, mainly zebuine, there's the Botucatu scale.

At the moment, the focus has been on facial scales. So, if we browse the literature we'll find scales for rabbits, for rats, and other animals as well. But before that, we should understand that every scale has its weakness.

What I recommend is using a scale that is best suited for your situation, if you are in a clinic, you cannot use overly complex scales. Now, if you are doing an experiment, the scales must be validated or, preferably, extensively used by the scientific community. There are also scales for the recognition of chronic pain.

Obviously, they were further developed in small animals than in large animals. I suggest you consult the description of this video, that has a list of all scale references, so you can read them at your own leisure. Pain management Regarding treatment, we will focus on acute and postoperative pain, OK?

This is just in order to follow the logic of our lessons, not that chronic pain isn't important, but we'll look that up further in future lessons. We have three levels of pain treatment, so we end up following degrees for the intensity of treatment. For mild postoperative pain, like dermorrhaphy or orquiectomy, we use anti-inflammatories and analgesic adjuvants.

For moderate pain such as elective ovariohysterectomy or removal of superficial tumours, we use partial opioid agonists, anti-inflammatories and adjuvant drugs. In case of severe pain, such as orthopedics, thoracotomy and exploratory laparotomy, we use potent opioids, such as total agonists, anti-inflammatories and adjuvants. Obviously, the treatment should not be a fixed standard or a cake recipe, we must be aware of the case, the patient and how the pain progresses.

With that, the following three video lessons will be addressing anti-inflammatory drugs, opioids and analgesic adjuvants. To sum it up, pain physiology is dynamic and the pain can persist if not treated adequately. All animals deserve adequate analgesic management, regardless of species.

In order to accomplish that, the familiarity with such species is essential to facilitate the recognition of pain in that patient. In the literature, there are several scales that can guide us in recognizing pain. Pain treatment must be in accordance to the patient, procedure and pain intensity, usually based on anti-inflammatories, adjuvants and opioids.

So guys, what did you think? Enjoyed this video lesson? I sure hope so, particularly because I really enjoy this subject.

I kindly invite you to leave a comment about the video, any doubts, suggestions, praises or criticisms, so that we can interact better, alright? Remember that the next videos will also be about pain and analgesia. For those who didn't subscribe yet, please do so, leave us a like, and share, that it’s very important for us.

See you soon! See you in the n. .

. next video l. .

. See you next video lesson, hugs. .

. I just botched the very end. .

. No. .

. The classes will be about this sub. .

. j. .

. it's about this height. .

. [what] Not this one. Terrible.

Hugs and see you soon. And now it worked.