Class 2 Analgesia & Pharmacology Flashcards
Describe the 1st stage pain pathway, and what dermatomes they are associated with.
- Lower uterine from contractions
- T10 - L1
Describe the 2nd stage pain pathway and it’s associated dermatomes.
- Perineal structure via pudenal nerve
- S2-S4 (not covered by epidural)
Opioids that cross the placenta can do what 2 things to the fetus?
- Loss of beat to beat variability
- Decreased movement
Name the 4 PCA advantages
- Satisfaction scores
- Less neonatal depression
- Less nausea
- Less maternal respiratory depression
Why is morphine not used?
-increased risk of respiratory depression r/t Immature BBB in baby
Demerol (meperidine) concerns
- Nausea and vomiting
- Baby respiratory depression unlikely if given < 1hr prior to delivery
- contraindicated with seizure / or renal failure (metabolite)
Fentanyl concerns
- Rapid placenta transfer
- resp depression longer than analgesia benefits
Nubain concerns
- Ceiling effect on respiratory depression
- Dysphoria
- treats opioid induced puritis
Stadol concerns
- Sedation
- Ceiling effect on resp depression
- better analgesic profile than fentanyl
Volatile agent concerns
- Rarely used
- pulmonary aspiration risk
- decreased uterine tone
- Supplement to nerve block
When is a pudenal block used, and on what patients?
- 2nd stage of labor
- pts with contraindication of neuraxial block
Risk of Pudenal block
- Fetal injury
- Infection
- Hematoma
when is a paracervical block used? What pain does it help with?
- When epidural cannot be achieved
- 1st stage labor
What are the complications of paracervical block?
- Uterine artery injection,
- fetal LA toxicity,
- nerve injury,
- hematoma
Ester local anesthetics.
- PABA
- Metabolized by plasma cholinesterase
- PABA metabolite is an allergen
- No previous “I”
Amide local anesthetic tidbits
- Metabolized by liver
- No PABA, allergic reactions rare
- 2 “i”s
Local anesthetics site of action?
-Neuronal cell membrane sodium channel
What determines the speed of Local anesthetic onset?
-pKa
To have a faster onset you would want pKa closer or farther away from physiological pH?
Closer
How can you artificially raise pH, to be closer to pKa?
-Add bicarb
Once across the membrane what form of drug is responsible for receptor binding and blockade?
-Polar form
What dictates the onset, quality and duration of a Local Anesthetic?
-Total dose
increasing dose =
faster onset and longer duration
How do vasoconstrictors effect LA?
- prevent absorption
- More available for blockade
How does temperature effect LA?
-Warm LA reduces onset time
How does pregnancy effect LA?
- Smaller amounts are required
- Faster onset
Small and poorly myelinated nerves, like type ____ fibers are ______ ______ susceptible to blockade.
- C
- More rapidly
Large, myelinated nerves like type ____ fibers require ______ concentrations of LA for blockade.
- A
- Higher
Local Anesthetic used for labor epidural.
- Bupivicaine
- Ropivacaine
- Lidocaine
Local Anesthetic used for operative epidural.
- Lidocaine
- 2-chloroprocaine
Local anesthetics used for OB spinal anesthesia?
- Tetracaine
- Bupivacaine
Lidocaine concerns
- Not for continuous infusion
- Test epidural catheter function
- Motor block
- activate epidural for C-section
- Short duration
2-chloroprocaine concerns
- only ester used in epidural space
- Rapid onset / short duration
- Large motor block
- low risk of toxicity
2-chloroprocaine will interfere with the analgesic effects of what med?
-Epidural fentanyl
Bupivacaine concerns (used at Hamot)
- Long duration
- Less motor block (can still feel contractions and push)
What happens if a large does of bupivicaine is given IV?
- CV collapse
- Refractory V-tach/V-fib
Benefits of levobupivicaine?
-less cardiotoxic
Ropivicaine benefit and problem.
- Less cardio toxic
- 25% less potent
What is the best lumbar level to cover in OB? Where should catheter be placed to achieve that level?
- T10 - S4
- L3 - L4
For 95% of OB, the spinal chord ends at? The other 5%?
- L1
- L2/3
What imaginary line passes between the iliac crests?
-Truffiers (about L3/4)
Contraindications to neuraxial block?
- Patient refusal
- Infection
- Intracranial mass
- Coagulopathy
- Aortic stenosis
- Spinal pathology
- Hemodynamic instability
On average the epidural space is how deep?
4.75 cm
How much of the tip should be in the epidural space?
-5 cm
What are the differences between spinal and epidurals?
- Spinal is one tissue layer deeper
- Drugs given via spinal are 10x more potent
- Spinals require smaller needle
When is a subarachnoid block used?
- C-sections
- Not enough time for epidural
Benefit and problem with combined spinal / epidural
- instant relief
- Cant test epidural catheter
Local anesthetic Central nervous system toxicity problems?
- Tinnitus
- Metallic taste
- Light headedness
- Circumoral numbness
- Convulsions
- LOC
- Respiratory arrest
Increase in what 2 things lower the seizure threshold?
- PaCO2
- Acidosis
How doe LA toxicity effect the CV system?
- Sodium channel inhibition
- Decrease depolarization of purkinjes fiber and ventricle muscle
- Decrease action potential
- Decrease refractory period
- Increased toxicity to bupivicaine and cocaine
LA toxicity is treated by what?
-20% intralipid
Subdural block is located where?
-Between dura and arachnoid matter
A subdural block may involve what?
- Cervical roots
- Cranial nerves
- Trigeminal block
- Horners syndrome
