Chapter 012. Pain: Pathophysiology and Management (Part 5)

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Sympathetically Maintained Pain Patients with peripheral nerve injury can develop a severe burning pain (causalgia) in the region innervated by the nerve. The pain typically begins after a delay of hours to days or even weeks. The pain is accompanied by swelling of the extremity, periarticular osteoporosis, and arthritic changes in the distal joints. The pain is dramatically and immediately relieved by blocking the sympathetic innervation of the affected extremity. Damaged primary afferent nociceptors acquire adrenergic sensitivity and can be activated by stimulation of the sympathetic outflow. A similar syndrome called reflex sympathetic dystrophy can be produced without obvious...

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Chapter 012. Pain: Pathophysiology and Management (Part 5) Sympathetically Maintained Pain Patients with peripheral nerve injury can develop a severe burning pain (causalgia) in the region innervated by the nerve. The pain typically begins after a delay of hours to days or even weeks. The pain is accompanied by swelling of the extremity, periarticular osteoporosis, and arthritic changes in the distal joints. The pain is dramatically and immediately relieved by blocking the sympathetic innervation of the affected extremity. Damaged primary afferent nociceptors acquire adrenergic sensitivity and can be activated by stimulation of the sympathetic outflow. A similar syndrome called reflex sympathetic dystrophy can be produced without obvious nerve damage by a variety of injuries, including fractures of bone, soft tissue trauma, myocardial infarction, and stroke (Chap.
370). Although the pathophysiology of this condition is poorly understood, the pain and the signs of inflammation are rapidly relieved by blocking the sympathetic nervous system. This implies that sympathetic activity can activate undamaged nociceptors when inflammation is present. Signs of sympathetic hyperactivity should be sought in patients with posttraumatic pain and inflammation and no other obvious explanation. Acute Pain: Treatment The ideal treatment for any pain is to remove the cause; thus, diagnosis should always precede treatment planning. Sometimes treating the underlying condition does not immediately relieve pain. Furthermore, some conditions are so painful that rapid and effective analgesia is essential (e.g., the postoperative state, burns, trauma, cancer, sickle cell crisis). Analgesic medications are a first line of treatment in these cases, and all practitioners should be familiar with their use. Aspirin, Acetaminophen, and Nonsteroidal Anti-Inflammatory Agents (NSAIDs) These drugs are considered together because they are used for similar problems and may have a similar mechanism of action (Table 12-1). All these compounds inhibit cyclooxygenase (COX), and, except for acetaminophen, all have anti-inflammatory actions, especially at higher dosages. They are particularly effective for mild to moderate headache and for pain of musculoskeletal origin.
Table 12-1 Drugs for Relief of Pain Generic Name Dose, Interval Comments mg NONNARCOTIC ANALGESICS: USUAL DOSES AND INTERVALS Acetylsalicylic 650 q4h Enteric-coated acid PO preparations available Acetaminophen 650 q4h Side effects PO uncommon Ibuprofen 400 q 4–6 h Available without PO prescription Naproxen 250– q 12 h Delayed effects 500 PO may be due to long half- life Fenoprofen 200 q 4–6 h Contraindicated
PO in renal disease Indomethacin 25–50 q8h Gastrointestinal PO side effects common Ketorolac 15–60 q 4–6 h Available for IM/IV parenteral use Celecoxib 100– q 12–24 Useful for 200 PO h arthritis Valdecoxib 10–20 q12–24 Removed from PO h U.S. market in 2005 Generic Name Parenteral PO Comments Dose, mg Dose, mg NARCOTIC ANALGESICS: USUAL DOSES AND INTERVALS Codeine 30–60 q 4 h 30– Nausea
60 q 4 h common Oxycodone — 5– Usually 10 q 4–6 h available with acetaminophen or aspirin Morphine 10 q 4 h 60 q 4h Morphine — 30– Oral slow- sustained release 200 bid to release preparation tid Hydromorphone 1–2 q 4 h 2–4 Shorter acting q4h than morphine sulfate Levorphanol 2 q 6–8 h 4 q Longer acting 6–8 h than morphine sulfate; absorbed
well PO Methadone 10 q 6–8 h 20 q Delayed 6–8 h sedation due to long half-life Meperidine 75–100 q 300 Poorly 3–4 h q4h absorbed PO; normeperidine a toxic metabolite Butorphanol — 1–2 Intranasal q4h spray Fentanyl 25–100 — 72 h µg/h Transdermal patch Tramadol — 50– Mixed 100 q 4–6 opioid/adrenergic h action
Ge Uptake S An O C R neric Blockade edativ ticholiner rthostat ardiac ve. ange, Name e gic ic Arrhy Dose mg/d Potenc Potency Hypote thmia , -HT E y nsion mg/ d ANTIDEPRESSANTSa D H Mo M L 7 oxepin + igh derate oderate ess 00 5–400 A H Hi M Y 2 mitriptyl +++ + igh ghest oderate es 50 5–300 ine I M Mo H Y 7 miprami +++ + oderate derate igh es 00 5–400 ne N M Mo L Y 4
ortriptyli ++ + oderate derate ow es 00 0–150 ne D L Lo L Y 5 esiprami ++ +++ ow w ow es 50 0–300 ne V L No N N 7 enlafaxi ++ + ow ne one o 50 5–400 ne D L No N N 3 uloxetin ++ ++ ow ne one o 0 0–60 e Generic P Inte Generi P Inte Name O Dose, rval c Name O Dose, rval mg mg ANTICONVULSANTS AND ANTIARRHYTHMICSa
Phenytoi 3 daily Clonaz 1 q 6 n 00 /qhs epam h Carbama 2 q6h Gabap 6 q 8 zepine 00–300 entinb 00–1200 h Oxcarbaz 3 bid Pregab 1 bid ine 00 alin 50–600