Good Morning

26 September 2002

Acute Postoperative Pain Management

麻醉科 林子富

Pathophysiology of Postoperative Pain

6 problems:1. Peripheral sensitization2. Constant bombardment of the CNS with noxious

input3. Noxious input processed by the CNS4. Pathophysiological consequences of acute pain5. Sensitization of the CNS response, called wind-up6. 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 extubation3. 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 activity2. Enlarged receptive field area3. 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– 4

1. 4 glutamate & 3 substance P receptor subtypes2. Different neurochemical mechanism mediated

by differing pain states3. 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

stimulusClinical 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

Management1. Prevent sensitization or

stimulation of peripheral receptors

Antihistamines NSAIDs Local anesthetics

Applying What We Know to Postoperative Pain

Management2. 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;89:98-103

IV coadministration of ketamine 50-100 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

Management3. 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