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
__mL of epidural anesthetic should be given as an incremental dose to avoid high spinals, sympathectomy, etc.
5
What epidural anesthetic additive would notify the CRNA that the epidural is placed in the venous space?
Epinephrine (injection = ↑HR)
________ will increase the duration of useful anesthesia with all epidural agents.
epinephrine.
Epinephrine’s effects are greatest seen with which two LA’s?
- Lidocaine
- 2-Chloroprocaine
Epinephrine’s effects are not as impressive with what LA’s?
- Bupivacaine
- Levobupivacaine
- Ropivacaine
What are the benefits of alkalinization of a local anesthetic?
- ↑ concentration of non-ionized drug
- ↑ rate of diffusion
- ↑ speed of onset
Name all the local anesthetics used for neuraxial anesthesia from those with a fast onset and short duration to those with a slow onset and long duration.
↑ Fast Onset / Short Duration
Chloroprocaine
Lidocaine
Mepivacaine
Ropivacaine
Bupivacaine
↓ Slow Onset / Long Duration
1mEq for every 10mL of anesthetic of this drug can be given to speed up onset of action of said anesthetic.
Na⁺HCO₃⁻
Sodium Bicarbonate
What concentration of chloroprocaine is used?
3%
What concentration of Lidocaine is used for epidurals?
2%
What concentration of Mepivacaine is used?
2%
What concentration of Bupivacaine is used?
0.5 - 0.75%
What metabolite of esters is important to know about?
PABA
What local anesthetic is for epidural use only? (never for spinals)
2-Chloroprocaine 3%
_______ has the greatest motor function depression while ______ has the least. (hint: local anesthetics)
Lidocaine = most motor blockade
Ropivacaine = Least
What drugs should be used when a patient is 8-10cm dilated and complaining of pain?
Opioids (local anesthetics will cause motor blockade and decrease ability to push)
Which epidural needle has the most curvature?
Tuohy (30°)
How long from the tip of the Tuohy needle to the hub?
9cm
What is the optimal catheter insertion depth for an epidural?
3-5cm
The distance, in the average adult, from skin to epidural space is what?
4-6 cm
What drug is used as a test dose for epidural placement?
Lidocaine 1.5% w/ 1:200k epinephrine
What sign/symptoms would indicate a positive test dose during an epidural anesthetic?
- HR ↑ by 20%
- Tinnitus
- Metallic taste
- Circumoral numbness
What will occur after a positive test dose is determined from an incorrect epidural placement?
- Significant motor block (now you’re intrathecal!)
- Peaked P-waves
- T-wave changes in children
