EPIDURAL ANESTHESIA

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General
Epidural needles
epidural catheters
specific techniques
activating an epidural
factors affecting the level of block
epidural anesthetic agents

General

-wider range of applications allowing for: cervical levels blocks, thoracic level blocks, and lumbar level blocks
-can be used as a single shot method similar to spinal anesthetics or with a catheter placement used intermittently/continously
-choice of anesthetic agent, dosage, concentration and level of injection can affect the degree of motor block from none to complete
-generally slower in onset than spinal anesthesia
-generally not as dense of a block compared to spinal anesthesia
-segmental blocks are possible using a more dilute anesthetic agent in combination with an opiod analgesic
-segmental blocks allow for sparing of the motor nerves and blocking the smaller sympathetic and sensory fibers
-segmental blocks used often in obstetrics and provides a well defined circumferential segment of blockade devoid above and below

Cervical epidural
-generally used clinically for pain management

Thoracic epidural
-increased risk of spinal cord injury compared to lumbar epidural placement
-most commonly used for intraoperative and postoperative pain management
-chronic pain can be managed with a single shot or use of catheter for multiple boluses or continuous infusion
-beneficial in providing postoperative analgesia especially in patients with underlying pulmonary conditions prone to shunting/splinting

Lumbar epidural
-most common anatomic location for the epidural site of insertion/injection
-generally can be used for majority of cases located below the diaghragm
-comparably less risk of spinal cord injury than with thoracic epidural due to spinal cord termination at L1(adults)

Often used for:
-operative anesthesia
-analgesic for obstetrics
-postoperative pain management
-chronic pain management

epidural needles
standard epidural needle generally is:
17 -18 gauge
3 to 3.5 inches long
beveled end which is blunted helps to push away and prevent puncture of the dura upon insertion
beveled end angulated approximately 15-30 degrees
tuohy needle most commonly used needle
crawford needle straight needle and possessing no curvature at the end

epidural catheters
-allows for intermittent boluses of anesthetic agent or a continuous infusion of an anesthetic agent
-allows for a prolonged duration of operative anesthesia with frequent or continuous infusion
-titration of anesthetics may allow for a total reduction of anesthetics used compared to large single bolus initally
-therefore may provide for more stable hemodynamics and less complications
-epidural catheter is usually 19 or 20 gauge
-epidural catheter is usually introduced through a 17 or 18 gauge epidural needle
-epidural catheter should generally be advanced 2 - 6 centimeters into the epidural space
-epidural advancement too far into epidural space: may lead to a more unilateral block due to the catheter migration anterolaterally
-epidural advancement too short into the epidural space may lead for the cathetor to slip out of the epidural space

specific techniques
-midline approach
-paramedian approach

Recognition of entering into the potential epidural space
-loss of resistance: of the glass plunger of the epidural syringe set
-hang drop technique: hanging drop of fluid becomes sucked in due to negative pressure once the ligamentum flavum is pierced
negative pressue do to the potential space of the epidura opening up and creating a sucking force

activating an epidural
-larger volume of anesthetic agents are generally required compared to spinal anesthetics
-due to the large volume of anesthetics used, there is an increased risk of toxicity of injected accidently intrathecally
-to help prevent large doses of unintentional intrathecal and intravascular injection of anesthetics, a test dose is performed

Test dose:
-local anesthetic in combination of epinephrine
3 ml of 1.5 % lidocaine with 1:200,000 epinephrine
therefore lidocaine 45 mg + 15 ug epinephrine

If test dose is injected intrathecal: will provide spinal anesthesia which will be rapidly noticed and therefore will not continue using
if test dose is injected intravascularly will create tachycardia and therefore will not continue to use the falsely placed catheter

Incremental dosing
-generally incremental dosing of 5 ml is injected through the epidural catheter after confirming placement with test dose/neg.asp.
-incremental dosing helps to avoid CNS and CVS complications if the catheter has migrated intrathecal or intravascularly

factors affecting level of block
-generally 1 - 2 ml of local anesthetic used for each segment to be blocked
ex. to block the level of T4 (level of the nipple) from site of injection of L4-5, then 12 - 24 ml of local anesthetic is needed
-less anesthetics are required with increasing age: perhaps due to decreased epidural space compliance with increasing age
-patients height affects the dosing of epidural anesthetics and generally require 2ml/ segment for tall and 1ml/segment for shorter pts
-patients weight generally has no significant affect on dosing of epidural anesthetic agents

Additives to local anesthetics affect: (ex. opiods, vasoconstrictors)
-quality of the epidural anesthetic block
-duration of the epidural anesthetic block

epidural anesthetic agents
-generally only preservative free anesthetic agents should be used for epidural anesthesia

Agents chosen based on:
-for primary anesthetic use
-for supplementation of general anesthesia
-for analgesia
-duration of anesthetic requirements
ex. short -intermediate acting anesthetic agents:
1.5 - 2 % lidocaine
3% chloroprocaine
2 % mepivicaine
ex. longer acting anesthetic agents:
0.5 - 0.75% bupivicaine
0.5 - 1 % ropivicaine
etidocaine

time to two-segment regression:
-intrinsic feature of each local anesthetic agent
-time it takes for a sensory level to decrease by two dermatomal levels
-generally can safely inject one-third to one-half the initial activation bolus dose when two segment regression has occured