- Pain can be classified according to pathophysiology
(eg, nociceptive or neuropathic pain), etiology (eg, postoperative
or cancer pain), or the affected area (eg, headache or low back
- Nociceptive pain is caused by activation or sensitization
of peripheral nociceptors, specialized receptors that transduce
noxious stimuli. Neuropathic pain is the result of injury or acquired abnormalities
of peripheral or central neural structures.
- Acute pain can be defined as pain that is caused
by noxious stimulation due to injury, a disease process, or the
abnormal function of muscle or viscera. It is nearly always nociceptive.
- Chronic pain is defined as pain that persists
beyond the usual course of an acute disease or after a reasonable
time for healing to occur; this period can vary from 1 to 6 months.
Chronic pain may be nociceptive, neuropathic, or mixed.
- Modulation of pain occurs peripherally at the
nociceptor, in the spinal cord, or in supraspinal structures. This
modulation can either inhibit (suppress) or facilitate (aggravate)
- Moderate to severe acute pain, regardless of
site, can affect nearly every organ function and may adversely influence
postoperative morbidity and mortality.
- Neural blockade with local anesthetics can be
useful in delineating pain mechanisms, but more importantly, it
plays a major role in the management of patients with acute or chronic
pain. The role of the sympathetic system and its pathways can be
- Antidepressants are generally most useful in
patients with neuropathic pain, eg, from postherpetic neuralgia
and diabetic neuropathy. These agents demonstrate an analgesic effect
that occurs at a dose lower than needed for their antidepressant
- Anticonvulsants have been found to be extremely
useful in patients with neuropathic pain, particularly trigeminal
neuralgia and diabetic neuropathy.
- Spinal cord stimulation is most effective for
neuropathic pain. Proposed mechanisms include activation of descending
modulating systems and inhibition of sympathetic outflow. Accepted
indications include sympathetically mediated pain, spinal cord lesions
with localized segmental pain, phantom limb pain, ischemic lower
extremity pain due to peripheral vascular disease, and adhesive
- Studies show that patient-controlled analgesia
(PCA) is a cost-effective technique that produces superior analgesia
with very high patient satisfaction. Total drug consumption is less,
compared with intramuscular injections. The routine use of a basal
(“background”) infusion is controversial.
- The administration of local anesthetic–opioid
mixtures neuraxially (particularly epidurally) is an excellent technique
for managing postoperative pain following abdominal, pelvic, thoracic,
or orthopedic procedures on the lower extremities. Patients often
have better preservation of pulmonary function, are able to ambulate
early, and benefit from early physical therapy. Patients may be at
lower risk for postoperative venous thrombosis.
- The most serious side effect of epidural or
intrathecal opioids is dose-dependent, delayed respiratory depression.
Most cases of serious respiratory depression occur in patients receiving
concomitant parenteral opioids or sedatives. Elderly patients and
those with sleep apnea appear to be particularly vulnerable and
require reduced dosing.
- Physical dependence occurs in all patients on
large doses of opioids for extended periods. A withdrawal phenomenon
can be precipitated by the administration of opioid antagonists.
- Multiple ...
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