Since its introduction to North America in 1942, the use of epidural
catheter analgesia has increased dramatically. Improved equipment, methods and medications have broadened its application to include among others, surgical
anesthesia,
chronic pain relief and the management of
postoperative pain. Numerous techniques for epidural
puncture and insertion of the
catheter have been described. Although complications have been associated with placement of an epidural
catheter, these are rare when performed by an experienced anesthesiologist.
Epidural analgesia was first accomplished by blockade with
local anesthetics.
Bupivacaine has been called the
local anesthetic of choice for epidural infusion. Bolus administration of epidural
local anesthetics gives effective
analgesia; however, its use is limited by brief duration and occasionally severe
hypotension. Epidural
local anesthetics have been administered by continuous infusion in an attempt to minimize side effects. Nevertheless,
hypotension, as well as motor block,
numbness,
nausea and
urinary retention have occurred.
Epidural analgesia with
local anesthetics is effective in relieving
postoperative pain, but its safety and feasibility have been questioned because of the frequent, potentially serious side effects. These problems led to trials of epidural
narcotics for
postoperative pain management. The exact site of action of epidural
narcotic analgesics is debatable; however, the bulk of evidence supports a direct spinal action. Epidural
narcotics appear to specifically inhibit nociceptive stimuli. The prolonged and profound
analgesia that occurs with epidural
narcotics relative to parenteral administration is due to a higher concentration of
drug reaching the CSF through the epidural route. Since nervous transmission is not completely blocked this technique cannot provide
anesthesia during operation.
Morphine has been the most frequently used
narcotic for
epidural analgesia. Results of several recent, randomized double-blind studies have shown that epidural
narcotics give adequate
analgesia comparable with that observed with epidural
bupivacaine. Epidural
morphine provides a greater duration of
analgesia and may cause fewer side effects. Improved
analgesia has been reported when epidural
narcotics are used in combination with
local anesthetics. Continuous administration of low dosage epidural
narcotics has been shown to have less frequent side effects than bolus administration. Nevertheless,
pruritus,
urinary retention,
hypotension and severe
respiratory depression have been reported with both methods.(ABSTRACT TRUNCATED AT 400 WORDS)