Epidural Anesthesia (Exam I) Flashcards
What benefits are provided via an epidural (versus a spinal) ?
- Predictable dermatome spread
- Slower onset
- Infusion (↑ duration)
- Maintain ability to ambulate and void (If placed above (below?) T10)
What are the disadvantages to epidurals?
- Longer time to place
- slower onset
- less dense block
What causes engorgement of the epidural venous plexus?
- Obesity
- Pregnancy
How does pKa affect onset of neuraxial anesthesia?
The closer pKa is to physiologic pH (7.4) the faster the onset.
What is the pKa of Lidocaine and prilocaine?
7.9
What drug is an exception to the pKa rule with an onset of action faster than lidocaine?
Why is this?
2-Chloroprocaine (pKa = 9) due to its 3% concentration.
What is the formula for pH?
pH = -log10 [H⁺]
What is the formula for Ka?
Ka = [H⁺][A-] ÷ [HA]
What is the formula for pKa?
pKa = -log(Ka)
What is the formula for Ka?
Ka = 10-pKa
Name the uptake of local anesthetics based on regional anesthetic technique (ex. IV vs SQ) in order from highest blood concentration to lowest.
What are the determinants of block spread with epidurals?
- Volume
- Site of injection
- Dose of LA
Increases in CVP (coughing, pregnancy, etc) will result in _________ epidural pressure and thus more ________.
increased; spread
How much will lumbar epidural injection flow caudad from the site of injection?
Trick question. Lumbar injections produce a preferential cephalad spread
To achieve a T6 sensory level block from an L3-L4 injection, how many mL of epidural anesthetic must be given?
11 - 22 mL at 1-2 mL per segment