Exam 1 - Neuraxial Principles (Part 4) Flashcards
What are the benefits of epidural anesthesia over spinal?
- Predictable dermatome spread
- Slower onset of autonomic blockade (slower hypotension)
- Unlimited duration
- Varying concentration of LA for analgesia or surgical anesthesia
- Maintain ambulation and voiding if the epidural is placed above T10 (segmental blockade)
What are the disadvantages of epidural anesthesia?
- Longer time to perform the technique
- Slower onset of effect
- Less dense block
What are the indications of epidural anesthesia?
- Upper and lower extremity surgery
- Can be used as a sole anesthetic or adjunct to GA (big lung cases).
- Post-op as a continuous infusion with or without patient-controlled epidural analgesia.
The epidural space extends from the _____ to the _______.
- From the skull to the sacral hiatus
What makes up the epidural space? Select 2.
A. fat
B. nerve roots
C. CSF
D. posterior longitudinal ligament
A Fat
B. Nerve roots
And: Areolar tissue, Lymphatics, and Veins/ Blood vessels
Why is blood vessel puncture common in pregnant patients during epidural block procedures?
- Engorgement of the epidural veins from caval compression
What can be done to open up the potential epidural space?
- Injection of saline (5 mL)
- Injection of air (1-2 mL)
Compare needle entry during an epidural block for cervical/lumbar region and thoracic region.
- Cervical/lumbar approach will be directed horizontally
- Thoracic approach needle pointed cephalad (40 degrees)
The safest point of entry into the epidural space is below the level of the ___.
A. foramen magnum
B. spinal cord
C. sacral hiatus
D. filum terminale
B. spinal cord
A line drawn between the superior aspect of the ________crosses either the spinous process of L4 or the L4-5 interspace.
- iliac crests
How does a drug’s pKa affect the onset of local anesthesia?
- The closer the pKa is to the physiological pH, the faster the onset of the effect.
What LA is the exception to the pka and pH rule for epidural onset?
- Exception: 2-chloroprocaine (pka: 9.0) 3%
- This is due to the high concentration of chloroprocaine at 3%
Faster onset than lidocaine
What is sham feeding?
- Sham feeding is any procedure that mimics normal food consumption but where food and drink are not actually digested or absorbed (ie: chewing gum).
- Sham feeding is a preventive measure for ileus
List the route of LA from fastest to slowest.
LA is injected into the epidural space via needle or catheter where the drug diffuses through the dural sheath of _______, __________, __________, and ______where nerve transmission is altered.
- Spinal nerves
- Roots
- Rootlets
- CSF
Generally, with epidural blocks, there is no _________ relationship with LA dosing.
- positional
What are the determinants of block spread in epidural anesthesia?
- Site of injection
- Volume dose of LA
What conditions will require a lower dose of LA for epidural anesthesia due to lower CSF volume?
- Age
- Pregnancy
- Obesity
- Little Person (Tyrion Lannister)
Why is a reduced volume of local anesthetic solution used during thoracic epidural block?
- Lower volume of LA d/t the potential of a higher block and hemodynamic instability
During an epidural block, how much volume of LA is required per segment?
- 1-2 ml per segment
For example, to achieve a T4 sensory level from an L4-5 injection, approximately 12–24 mL of local anesthetic should be administered (incremental dosing)
What is the volume used for incremental dosing for epidural blocks?
- 5 mL of LA
Incremental dosing with 5 ml avoids:
- Accidental “High spinal”
- Hypotension from rapid autonomic blockade (cardiac arrest)
- Local Anesthetic toxicity
If epi is added to LA, it can be used as a marker/indicator that medication has been injected into the blood vessel. (↑HR)
What are the purposes of using additives for Epidural Anesthesia?
- Prolong epidural block
- Improve the quality of the block
- Accelerate onset of block
