Good Morning 26 September 2002

Acute Postoperative Pain Management 麻醉科 林子富

Pathophysiology of Postoperative Pain 6 problems : 1. Peripheral sensitization 2. Constant bombardment of the CNS with noxious input 3. Noxious input processed by the CNS 4. Pathophysiological consequences of acute pain 5. Sensitization of the CNS response, called wind-up 6. Induced sensitivity in the nervous system outlasts the stimulus

1. Peripheral sensitization

2. Constant bombardment of the CNS with noxious input

3. Noxious input processed by the CNS Adverse spinal reflexes, such as muscle spasm and sympathetic stimulation, are provoked. Supraspinal reflexes incite the mediators of the stress response.

A Multimodal Approach to Control Postoperative Pathophysiology and Rehabilitation in Patients Undergoing Abdominothoracic Esophagectomy Brodner G, Pogatzki E, Van Aken H, et al. Anesth Analg 1998;86:228 – 34 Multimodal regimen: 1.Effective thoracic epidural analgesia Establishing epidural blockade intraoperatively Patient-controlled postoperative epidural analgesia (PCEA) Continuous evaluation and treatment of postoperative pain by an acute pain service 2.Early tracheal extubation 3.Forced mobilization

4. Pathophysiological consequences of acute pain (  ) Cardiovascular Pulmonary Gastrointestinal Renal tachycardia, hypertension, increased SVR, increased cardiac work hypoxia, hypercarbia, atelectasis; decreased cough, VC, FRC; ventilation perfusion mismatch nausea, vomiting, ileus, NPO oliguria, urinary retention

4. Pathophysiological consequences of acute pain (  ) Extremities Endocrine Central nervous system Immunologic skeletal muscle pain, limited mobility, thromboembolism vagal inhibition; increased adrenergic activity, metabolism, oxygen consumption anxiety, fear, sedation, fatigue impairment

Physiologic Impact of Epidural Analgesia Lower rates of deep venous thromboses Lessening myocardial ischemia Decreasing pulmonary morbidity Positive consequences on recovery of gastrointestinal function

5. Sensitization of the CNS response Central sensitization refers to enhanced excitability of dorsal horn neurons and is characterized by: 1. increased spontaneous activity 2. Enlarged receptive field area 3. An increase in responses evoked by large and small caliber primary afferent fibers Windup refers to the progressive increase in the magnitude of C-fiber evoked responses of dorsal horn neurons produced by repetitive activation of C-fibers. Triggered by neurotransmitter glutamate and neurokinin peptides (substance P)

Reversing Tissue Injury-Induced Plastic Changes in the Spinal Cord: The Search for the Magic Bullet Raja SN, Dougherty PM. Reg Anesth Pain Med 2000;25:441– glutamate & 3 substance P receptor subtypes 2.Different neurochemical mechanism mediated by differing pain states 3.There may be no single “ magic bullet ” that blocks central sensitization and the result secondary hyperalgesia.

6. Induced sensitivity in the nervous system outlasts the stimulus  Clinical pain Low-threshold Sensitization following injury Allodynia Hyperethesia hyperpathia  Physiologic pain High-threshold Serve to warm the organism of harm ? Can we avoid total analgesia and block only the clinical pain ? The sophisticated goal of preemptive analgesia to achieve a differential effect on physiologic and clinical pain

Preemptive Epidural Analgesia and Recovery From Radical Prostatectomy Gottschalk A, Smith DS, Jobes DR, et al. JAMA 1998; 279:1076 –82.

Applying What We Know to Postoperative Pain Management 1. Prevent sensitization or stimulation of peripheral receptors Antihistamines NSAIDs Local anesthetics

Applying What We Know to Postoperative Pain Management 2. Diminish or eliminate the bombardment of the CNS with nociceptive input Peripheral nerve blocks Intrathecal or epidural analgesia Systemic opioids Small-dose IV ketamine

Small-Dose Ketamine Enhances Morphine- Induced Analgesia After Outpatient Surgery Manzo Suzuki, Kentaro Tsueda, et al. Anesth Analg 1999;89: IV coadministration of ketamine μg/kg with morphine 50 μg/kg 15 min before the end of the operation 1.Although opiates produce antinociception through μ receptor agonist activity, they activate NMDA receptors, resulting in hyperalgesia and the development of tolerance to opiates. 2.The marked reduction in both pain score and morphine requirement may be explained by the interaction of ketamine with NMDA receptors that had been activated by perioperative nociceptive inputs, as well as by the administration of morphine.

Applying What We Know to Postoperative Pain Management 3. Continue treatment until the inflammatory reaction that fuels the nociceptive input is minimized Sustained release opioids Consultation with a pain psychologist

心得感想 … For humanitarian reasons… Why postoperative pain must be treated effectively… The value of “multimodal” or “balanced analgesia” in postoperative pain management…

Have A Nice Day