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Types of pain: 1- Nociceptive pain, divided into A) Somatic : most often presents as throbbing and well localized pain and responds well to NSAIDs. B) Visceral: Can manifest as a referred (coming from other structures) or a well localized pain. 2- Neuropathic pain Pain that is associated with actual physical nerve damage or irritation. More Details regarding those two types would be mentioned later. The five stages of nociception are stimulation, transmission, modulation, perception and adaptive inflammation. * Pain transmission: Different neuronal fibers transmit pain's signal as an action potential to the brain. The larger the diameter of the fiber , the more insulated it is and the faster the signal transmission is through it. Nociceptive transmission takes place in Aδ and C nerve fibers. A delta (Aδ) fibers have large diameters, they're myelinated and are responsible for rapid conduction of electrical impulses associated with thermal and mechanical stimuli, where there is a risk of severe tissue damage if the response is delayed. E.g.: in the case of burning, a thermal stimulus, a delayed response would lead to significant tissue damage and to avoid unnecessary and maybe life threatening injury, the signal must be conducted as soon as possible to allow for an immediate reflex. A reflex means that the signal needn't get to the brain and the spinal cord would mediate a quick response through motor neurons. The pain associated with this type of neuronal fibers, Aδ, is usually described as intense, acute and of sharp or stabbing nature that alerts the subject to injury or insult to tissues. However if the trigger is not life threatening , although irritating to the subject , the impulse is transmitted via C fibers; unmyelinated fibers that are small in diameter and release glutamate(excitatory neurotransmitter in the brain), substance P and CGRP which is a peptide in the brain associated with stimulatory pathways and headaches. Fibers C convey mechanical and thermal signals that are not life threatening or do not cause immediate and serious injury to the body , like neuropathic pain as in the case of diabetic neuropathy , which is uncomfortable to the patients due to tingling, numbness and burning sensation but it is not life threatening and doesn’t require a fast response in milliseconds. The pain associated with this type of neuronal fibers, C fibers, is usually described as dull (not specified or localized) , aching and burning pain and sometimes it is called the second pain, because it is perceived after the first pain sensation which was mediated by A delta fibers. An example is patients with MI, where pain would radiate to other areas. The second pain , is pain that occurs after the initial pain signal , and it is transmitted through C fibers. Keep in mind that both fibers are parts of the same system but each specifies for a specific physiological function. A potential intervention in this phase would be to block the stimuli from binding to the nociceptive receptors (the pain triggering receptors at the neurons) then the pain could be modulated. *Modulation of the pain signal: happens when the signal reaches the spinal cord to move on to the brain , and either excitatory or inhibitory neurotransmitters are released and here is where the pain signal, regardless of the initial stimulus, is modulated. * Pain Perception: Perception is the processing of the pain signal that occurs in the brain and it differs from an individual to another. For example, an emotionally healthy, happy man would have a higher pain threshold. Meaning that while the same stimulus that causes him mild to moderate pain would cause someone with physical or psychological issues severe pain because he would have a lower pain threshold and a higher susceptibility to pain. The reason behind that is that the processing in the brain , the perception, differs between them. *Adaptive inflammation After the person is subjected to an injury , an acute inflammation takes place, where inflammatory mediators are released. Those inflammatory mediators trigger pain , by binding to the nociceptive receptors thus decreasing the pain threshold, making the injured area more sensitive to pain, ultimately decreasing the movement of the afflicted area and optimizing its healing. After healing, the inflammation should subside along with the pain. Although, sometimes maladaptive inflammation occurs and pain persists despite healing resulting in a type of neuropathic pain called functional pain, where actual damage or pain triggers are absent but improper pain signals are present making it self sustained (without a trigger). In nociceptive pain the treatment aims to cure, while in neuropathic pain the target is to improve or regain functionality in the afflicted part as cure is unlikely achievable by pharmacologic or nonpharmacologic treatments unless there is an obvious reason for the nervous damage and it is corrected via surgery , such as in the case of degenerated discs operations , as a vertebrae compresses a nerve and results in neuropathic pain and pharmacologic agents couldn't result in a cure , a surgery would target the reason for the damage allowing the healing and recovery of the nerve. Classification of pain, according to duration and prognosis: 1- Acute Pain: Caused by surgeries, acute illnesses, trauma and labor. Acute pain usually is nociceptive and lasts from a few hours up to months, but never more than 6 months and can be successfully managed with NSAIDs, especially the somatic kind. 2- Chronic pain is defined as pain that persists for 6 months to several years. It serves no biological protective purpose causing undue stress and suffering. - Insomnia and depression are unusual in acute pain but common in the case of chronic pain. As the psychological component is a major issue in chronic pain, the key to a successful management rests on the prevention and elimination of unnecessary suffering and despair. Using cognitive interventions and physical therapies as well as pharmacologic agents is helpful. While nociceptive pain usually results in acute pain, neuropathic with chronic pain , but exceptions are present in both cases. An example of acute neuropathic pain is in the case shingles, caused by the Varicella Zoster virus. It causes moderate to severe pain , usually severe that lasts for few days. Even with supportive treatment with an antiviral, the virus won't be eradicated, but the pain would subside( typically within two weeks). The main difference between acute and chronic pain is predictability, ,ie , the ability of the patient or health care taker to predict the type , severity and duration of pain from day 1; as long as the progression is known or predictable it is considered acute pain , if it couldn’t be predicted even from day 1 , then it's considered chronic. Example : In a patient with pharyngitis, from the first day it's known that the peak of pain would be in the first couple of days, in three to four days it will diminish or decrease gradually and in 7 to 10 days it will be gone even without antibiotic treatment and since the progression of the pain is know, it is called acute pain. While if a patient has diabetic neuropathy , it is unknown whether the intensity and the pattern of the pain will change and a remission is unpredictable, classifying it as a chronic type of pain. Treatment: First line of treatment for neurologic pain is drugs that stabilize neuronal membranes to prevent the travelling of impulses and action potentials , thus treatment with anticonvulsants or antiepileptic drugs and antidepressants such as TCA or SSRI is recommended. The treatment of nociceptive pain depends on its the severity. There are several tools or scores that evaluate the severity of the pain , but always keep in mind that pain is very subjective and depends on the patient in the first place. The facial pain score is one of the most famous tools to evaluate the severity of the pain, it categorizes pain into grades from 1 to 10. Zero indicates the absence of pain, 1-3 mild/minor pain, 4-6 is moderate pain and 710 indicates severe pain. To consider the pain medication effective , it should reduce the pain by 1 category ( severe to moderate or moderate to mild). (A reduction from 10 to 8 is considered ineffective). Ideally a goal of mild to no pain is aspired to, but that depends on the nature of pain, but as an initial assessment of the medicine's efficacy one pain category is enough. Treatment : - In the case of mild pain : a non-opioid mild analgesic like paracetamol is used plus an adjuvant like caffeine or antihistamines. Panadol extra contains caffeine ,although caffeine is mostly effective in case of headaches than in the other types of pain. It is considered an adjuvant. Adjuvants can also be antiemetics such as promethazine; which has antihistaminic and antiemetic actions and reduces pain along with other agents. -In the case of moderate pain, the patient is given weak opioids such as tramadol or codeine with or without non-opioid analgesics like acetominaphen or NSAIDs and with or without an adjuvant. -In the case of severe pain , the patient is given a strong opioid, with or without nonopiods like acetominaphen or an NSAIDS , with or without an adjuvant. IV opioids' efficacy is evaluated within 15 minutes, while in 1 hour for oral dosage forms, then the dose is titrated, depending on the pain severity. If the pain wasn't affected , the dose could be doubled. In cases of severe pain like in cancer patients , the patient is usually given two forms of the same drug; extended release and immediate release for pain breakthroughs, to provide full coverage. Note : In moderate to severe pain add on therapies including medications that treat neuropathic pain could be included because in the severe nociceptic pain it is possible to have a neuropathic component. Regardless of the pain severity (mild, moderate, severe) or classification (acute, chronic), the treatment should be scheduled around the clock (ATC), not PRN. Eg, three times daily regardless of the symptoms severity as that prevents the fluctuation in the pain signals which leads to variation refractoriness in the responsiveness to the treatment. Note : three times daily refers to administering the dose three times while the patient is awake , ie , taking three doses from the time the patient wakes up till the time he or she goes to bed , whereas Every 8 Hours strictly implies that a dose must be taken every 8 hours regardless of sleeping patterns Please note that there were many slides that weren’t covered in this lecture , this sheet contains everything that the Doctor mentioned as well as some explanatory texts taken from the slides to help making the mentioned points clear Good luck