Lecture 6: Pain

Lecture 6: Pain Assessing Pain · Acute pain is often a physical warning mechanism · LATERSNAPS · Radiating/referred pain: pain stimulus travels along a spinal nerve and may have interneuronal communication with adjacent spinal nerves · Quality: burning, dull, sharp etc. · Severity: “how bad is your pain?” ↳ scale of 0-10 ↳ pediatric faces tool PNS Receptor Types Pain Transduction · pain transduction begins when a receptor in the PNS is stimulated from local tissue injury and chemical mediators are released · sensory information from PNS to CNS ↳ starts at sensory receptor on body part then ends in somatosensory cortex ↳ afferent pathway · the sensory impulse needs to be strong enough to reach threshold (-30mv) Pain Transmission and Perception · nociceptors → A or C fibers (1st order neuron) → spinal cord → substance P neurotransmitter passes info to 2nd order neuron → decussates and travels up spinothalamic tract to the thalamus → synapse with 3rd order neuron → somatosensory cortex for perception and awareness of pain · A fibers are myelinated and include fast pain, C fibers are unmyelinated and include slow pain - - Neurotransmitters in Pain Sensation ① Substance P (excitatory) · acute pain transmission · receptors: mu, Kappa, delta, sigma, epsilon ② Glutamate (excitatory) · usually chronic pain, neuropathic pain, hyperalgesia (hypersensitivity) · receptors: NMDA Acute Pain · up to 10 days but can persist up to 6 months · self limiting → endogenous inhibitors secreted · SNS responses active · innate protective mechanism · aggressive treatment is effective Chronic Pain · longer than 6 months · not self-limiting → no endogenous inhibitors · SNS responses not active · destructive mechanism (chronic inflammation) bad for host · triggers other dysfunctions: insomnia, anxiety, anorexia, depression · treatment is not effective, requires other interventions Pain Terminology · visceral pain: deep pain, organ related · Cutaneous pain: superficial pain, surface related · referred pain: pain travels or "radiates" due to body surface innervated by same spinal nerve plexus · chronic pain: persistent pain ↳ likely travels along C fibers ↳ inflammation in the nerve area: "neurogenic inflammation" ↳ common with untreated acute pain or chronic inflammation disorders · hyperalgesia: persistent, often unexplained cause of pain/hypersensitivity ↳ complex regional pain syndrome (CRPS) · neuropathic pain: persistent nerve irritation → hard to treat, usually post trauma · Phantom pain: neuropathic pain present without stimulus, post amputation ↳ spinal cord neurons are still active despite lack of stimulus (nociceptor) ↳ interneurons still communicating it → becomes chronic Flexor Reflex/Withdrawal Reflex · sharp pain stimulus → reflex withdrawal without cerebral control · activation of a sensory neuron (afferent) → interneuron in CNS → automatic activation of a motor neuron (efferent) → response (withdrawal) by effector · often a protective mechanism Pain Gate Theory · rubbing the area you hurt makes brain stop impulse of pain for short time Non-Pharmacological Pain Management: ice, massage, distraction, physio, hypnosis, meditation, CBT, TENS (nerve stimulation), acupuncture, etc. I endogenous septide ↳ binds Endogenous Response to Pain (efferent) · reduced pain sensation · endogenous opioid peptides: endorphins, enkephalins, dynorphins ↳ inhibitory neurotransmitters or neuromodulators ↳ released from hypothalamus, limbic system, reticular formation ↳ binds to opioid receptors and prevents substance P release · induced secretion of serotonin and norepinephrine → reduced pain ↳ NE binds to opioid peptide receptors Common Routes of Administration: · IV ↳ PCA (patient controlled analgesia) · PO ↳ extended release options · Intranasal . PR · Other: epidural, spinal, nerve block Analgesia Pain Treatment ① At CNS level · non-opioid centrally acting agents ↳ acetaminophen (Tylenol) · opioid analgesics ↳ eg. morphine ② At peripheral level · NSAIDS ↳ eg. Ibuprofen (advil), ASA High efficacy against inflammation Inhibits Acetaminophen (Tylenol) Active metabolite · centrally acting analgesic (NOT anti-inflammatory) ↳ usually administered PO; q4h · antipyretic ↳ highest efficacy for fever ↳ reduces fever by stimulating the hypothalamus to vasodilate · Weak prostaglandin inhibitor Binds to these receptors - - Acetaminophen ADME · Absorption ↳ PO excellent bioavailability ↳ Cmax 30-60 min · Well Distributed ↳ low (20% ) PPB · Active Metabolites ↳ hepatic metabolism CYP 3A4 & 1A2 ↳ hepatotoxic metabolite: N-acetyl benzo · Renal Excretion ↳ t1/2: 2-3hrs Opioid Terminology · Opioid: any drug that is derived from the opium formula (white poppy) ↳ contains morphine and codeine substances · Narcotic: describes any CNS depressing substances ↳ terminology is associated with illegal use ↳ terminology used in clinical settings to imply the drug is monitored · Controlled dispensing and prescribing ↳ most are schedule 1 (some are schedule 2) ↳ prescribing monitored Opioids "Opium-like" mu1 agonist · centrally acting analgesics r · agonists for receptors mu, Kappa, delta · binding inhibits release of substance P → reduces pain · used for moderate-severe pain (8/10 pain scale) PPUTT Combination Drugs: · Percocet (oxycodone + acetaminophen) · Percodan (oxycodone + ASA) · Vicodin (hydrocodone + acetaminophen) · Tramacet (Tramadol + acetaminophen) · Tylenol #1, 2, 3, 4 (acetaminophen + codeine + caffeine) ↳ increasing amount of opioid (codeine) ① High Efficacy Opioids (8/10 pain) FHMMM · fentanyl · hydromorphone (Dilaudid) · meperidine (Demerol) · morphine · methadone (Metadol) ↳ used to wean off of high efficacy opioids ② Moderate Efficacy (6-7/10 pain) HOOT · hydrocodone, oxycodone (OxyNeo), oxycontin, tramadol (Ultram) · combo drugs: percocet, percodan, vicodin, tramacet · codeine → combo with tylenol 1-4 Opioids ADME · Intermediated PPB (30% ) ↳ varying affinity ↳ lipophilic → can be stored in fatty tissues of obese patients ↳ quickly distributed from bloodstream into tissues · Metabolism ↳ hepatic metabolism ↳ codeine metabolized into morphine b/c prodrug (CYP 2D6 & 3A4) · Excretion ↳ renal excretion Opioid OD Treatment ↳ bile → biliary recirculation · opiod receptor antagonists · Naloxone (Narcan) Common Side Effects: ↳ onset 2-4 mins · CNS depression ↳ duration of action 45 mins · CNS effects · Treatment of opioid dependence: · Nausea & Vomiting methadone protocol · Pruritus (itchy Skin) · Constipation · Urinary retention Pain Rating Treatment Options · <4/10 ↳ non-opioids (NSAIDS, Tylenol) ↳ less invasive PO route · 4-6/10 ↳ opioids (combination drugs, morphine) ↳ less invasive PO route · >6/10 ↳ higher potency opioids ↳ consider IV route ↳ consider PCA or addiction Fever + Treatment · Fever is a non-specific, protective defence mechanism used to destroy pathogens · stimulated by release of pyrogens and pro-inflammatory mediators ↳ CNS: hypothalamus triggered · high fever may increase metabolism but decreases cellular functioning · Treatment: Antipyretics ↳ 1st choice: acetaminophen (Tylenol)!!! * - no Rye's syndrome, PO q4h ↳ 2nd choice: NSAIDs (ibuprofen, ASA) ⑧ O - * * Addiction · physiological addiction: patient's body gets used to feeling b/c of medications · psychological addiction: behaviours of the patient to seek that feeling or substance · 4 C's of Addiction ↳ loss of control over use ↳ use despite consequences ↳ compulsion to use ↳ craving - - - - Other Types of Treatment · Inflammation ↳ allergy: antihistamines ↳ tissue injury: NSAIDs, biologics per diagnosis ↳ glucocorticoids ↳ Beta 2 adrenergic agonists (bronchoconstriction) · Pain ↳ acetaminophen (Tylenol) ↳ NSAIDs ↳ opioids · Fever ↳ acetaminophen* ↳ NSAIDs (Kinda? ) · MI pain ↳ morphine (opioid) · Headache ↳ ibuprofen (Advil) ↳ ASA → also helps w/blood clots · GI pain ↳ dicyclomine (Bentyl) - muscarinic antagonist - GI Smooth muscle relaxant