Acute Postoperative Pain Management

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Good Morning
26 September 2002
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Acute Postoperative Pain Management

• ??? ???

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Pathophysiology of Postoperative Pain

• 6 problems
• Peripheral sensitization
• Constant bombardment of the CNS with noxious
  input
• Noxious input processed by the CNS
• Pathophysiological consequences of acute pain
• Sensitization of the CNS response, called wind-up
• Induced sensitivity in the nervous system
  outlasts the stimulus

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1. Peripheral sensitization
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2. Constant bombardment of the CNS with noxious
input
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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.

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A Multimodal Approach to Control Postoperative
Pathophysiology and Rehabilitation in Patients
Undergoing Abdominothoracic EsophagectomyBrodner
G, Pogatzki E, Van Aken H, et al. Anesth Analg
199886228 34

• Multimodal regimen
• 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
• Early tracheal extubation
• Forced mobilization

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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

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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

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Physiologic Impact of Epidural Analgesia

• Lower rates of deep venous thromboses
• Lessening myocardial ischemia
• Decreasing pulmonary morbidity
• Positive consequences on recovery of
  gastrointestinal function

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5. Sensitization of the CNS response

• Central sensitization refers to enhanced
  excitability of dorsal horn neurons and is
  characterized by
• increased spontaneous activity
• Enlarged receptive field area
• 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)

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Reversing Tissue Injury-Induced PlasticChanges
in the Spinal CordThe Search for the Magic
Bullet Raja SN, Dougherty PM. Reg Anesth Pain
Med 200025441 4

1. 4 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.

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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
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Preemptive Epidural Analgesia and Recovery From
Radical ProstatectomyGottschalk A, Smith DS,
Jobes DR, et al. JAMA 19982791076 82.
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Applying What We Know to Postoperative Pain
Management

• 1. Prevent sensitization or stimulation of
  peripheral receptors
• Antihistamines
• NSAIDs
• Local anesthetics

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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

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Small-Dose Ketamine Enhances Morphine-Induced
Analgesia After Outpatient SurgeryManzo Suzuki,
Kentaro Tsueda, et al. Anesth Analg 19998998-103

• IV coadministration of ketamine 50-100 µg/kg with
  morphine 50 µg/kg 15 min before the end of the
  operation
• Although opiates produce antinociception through
  µ receptor agonist activity, they activate NMDA
  receptors, resulting in hyperalgesia and the
  development of tolerance to opiates.
• 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.

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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

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????

• For humanitarian reasons
• Why postoperative pain must be treated
  effectively
• The value of multimodal or balanced analgesia
  in postoperative pain management

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Have A Nice Day