Lecture 2 - Labor Analgesia & Pharmacology Flashcards
Pain pathways for 1st stage are:
Pain source is mainly lower uterine segment from contractions (T10 - L1 dermatomes)
Pain pathways for 2nd stage are:
source is perineal structures via pudendal nerve (S2 - S4 dermatomes)
What is important to know about hypnosis:
- 15% of population easy to hypnotize and 15 % are impossible to hypnotize
- may be of some benefit in labor but not very useful by itself.
What is important to know about Psychoprophylaxis?
(LAMAZE)
- Involves education and behavioral techniques
- Combined with other forms of analgesia
What is important to know about Acupuncture?
- During acupuncture opioid peptide release has been demonstrated
- ??Gate Control Theory?? (over stimulation of an area in pain)
Morphine has what effect on mother and neonate?
-immature blood brain barrier increases risk of respiratory depression in the neonate
Meperidine (Demerol) has what effect on mother and neonate?
- Neonate respiratory depression unlikely if given less than 1 hour prior to delivery
- Contraindicated in pt with seizure or renal issues
- Kinetics half life is 18-23 hours in neonate
Fentanyl has what effect on mother and infant?
- Respiratory depression may outlast analgesia
- PCA recipe loading dose 1 - 2 mcg/kg: dose 50 mcg with 10 minute lockout
- use pulse oximetry
Nalbuphine (Nubain) has what effect on mother and infant?
- Has ceiling effect on resp depression
- Dysphoria common
- Treats opioid induced pruritis
- Mu Opioid antagonist, Kappa agonist
Butorphanol (Stadol) has what effect on mother?
- Sedation Common
- ceiling effect on resp. depression
Volatile agents have what effect on mother and infant?
- Rarely used
- Dose limit 0.5 MAC
- Decreased uterine tone
- Often used with supplemental nerve block
What can be said about Paracervical block?
-1st stage of labor
-5 cc of local injected at submucosally at 3 and 9 o’clock position beside cervix
RISKS:
- Accidental injection into uterine artery
-Fetal local anesthetic toxicity
-nerve injury and hematoma
What can be said about pudendal block?
-2nd stage of labor
-Good alternative for patients with contraindications for neuraxial block
-injection bil. via trans-vaginal approach under the ischial spines
RISKS:
-Fetal injury
-infection
-hematoma
Amino esters concerns are:
- Metabolized by cholinesterase
- Para aminobenzoic acid (PABA)
- One “i” in the name
T/F: Para aminobenzoic acid is a known allergen.
TRUE
Amino amides concerns are:
- Amide leadage (metabolized by liver)
- NO PABA
- Two “i” in the name
Lipid solubility can do what:
- Increase potency
- Enhances placental diffusion
Protein binding can do what:
- Influence duration
- Higher protein binding decreases placental diffusion
- A1-acid glycoprotein (High affinity-low capacity)
- Albumin (Low affinity-high capacity)
T/F: Local anesthetic agents are all weak acids.
FALSE (…all weak bases.)
What will volume and concentration of a local anesthetic dose do?
Dictate onset, quality, and duration
Increasing does - faster onset, longer duration
Vasoconstrictors will do what to a local anesthetic?
-Prevent absorption via vascular beds, therefore more La available for blockade.
Temperature does what to a local anesthetic?
-affects onset, with warmed LA reducing onset time
Local anesthetic has what affect on pregnancy?
-Smaller amount of local anesthetic are needed
-faster onset of blockade
(Progesterone could possibly be the reason)
What local anesthetics are commonly used for labor epidural analgesia?
- lidocaine
- bupicavaine
- Ropivacaine
What local anesthetics are commonly used for operative epidural anesthesia?
- Lidocaine
- 2 -chloroprocaine
What local anesthetics are commonly used for spinal anesthesia?
- Bupivicaine
- Tetracaine
Lidocaine concerns in OB are:
- Labor epidural not used for continuous infusion
- Top up and to test function of epidural catheter
- Short duration ~45 minutes
- activate epidural catheter for C-section (15-20 cc of 2%
A lot of motor block with lidocaine during a epidural is a good thing.
FALSE
What is the dose of 2 chloroprocaine for a Csection?
15-25 cc of 3% (redose give 5 cc at a time)
Details about 2 chloroprocaine:
- Only ester used in epidural space
- rapid onset, short duration
- lot of motor block
- metabolized by pseudocholinesterase
- interfere with fentanyl’s analgesic effects
- Not for spinals
Bupivaciane dose for epidural is:
- Initial 15-20 mg (7.5 - 10cc of 0.2%)
- Infusion 8-12 mg ( 8 - 10 cc of 0.1%)
What can be said about bupivicaine?
- Long duration
- less motor block than other agents
- Produces refractory v-tach/v-fib if large IV does given.
What about levobupivacaine?
- L-isomer of bupivicaine
- less cardiotoxic
- New and very expensive
- not approved for spinal
What about ropivacaine?
- Bupivacaine analog
- less cardio toxic than levobupivacaine
- 25% less potent than bupivicaine
- not approved for spinal
T/F: For obstetrics lumbar level is best to cover T-5 thru S4 dermatones.
False (…T-10 thru S4 …)
In __% of patients the spinal cord ends at L2/L3, therefore spinals should be placed as low as possible and below __.
5
L3
_________ line passes across the lumber spine between the posterior iliac crests
Tuffier’s (L3/L4)
What are the contraindication to neurasxial blockade?
- Patient refusal
- Infection at the site of injection
- Coagulopathy (Liver failure, anticoagulats, HELLP syndrome, thrombocytopenia …)
- Intracranial mass lesion
- aortic stenosis
- Existing spinal or neurological pathology
- Hemodyamic instability
Epidural spae on average identified at ___ cm deep.
4.75
After space identified thread catheter until __ cm of the tip lie in the epidural space.
5
T/F: If placement of the catheter in an epidural fails withdrawal the catheter while leaving the needle in place to reposition.
FALSE (Never withdrawal the catheter through the needle!)
Difference between epidural and spinal block is one ______ layer (a few millimeteres) but drugs delivered via spinal route are ~ ___ more potent and much smaller needles are used (______ gauge for spinal vs. _____ gauge for epidural)
tissue
10x
22-27
17-18
Important points about subarachnoid blocks for labor?
-More often used for C-section
-Combination of opioid and local anesthetic
(Sufenta 5-10 mcg or fentanyl 10-20 mcg and bupivacaine 2mg)
-Quickly done when there is no time for epidural
-Combination of epidural and spinal are done too.
Important points about a combination of spinal and epidural:
- Provides nearly instant relief
- Problem is it makes testing epidural catheter difficult
What are the S/S of local anesthetic toxicity for the CNS?
- Tinnitus
- Light-headedness
- Metallic taste
- Circumoral numbness
- Convulsions
- Loss of consciousness
- Respiratory arrest
T/F: A higher potency of local anesthetic requires less total dose required for toxicity.
TRUE
T/F: A decrease in PaCO2 and acidosis lowers seizure threshold when using a local.
FALSE (A increase in PaCO2…)
T/F: Acidosis decreases protein binding which allows more free local anesthetic.
True
What are the S/S of local anesthetic toxicity of the cardiovascular system?
- Inhibition of cardiac sodium channels
- Decrease the rate of depolarization in Purkinje’s fibers and ventricular muscle
- Decrease duration of action potential and effective refractory period
- Increased toxicity to bupivacaine and cocaine with pregnancy.
What is the treatment for local anesthetic toxicity?
- 20% intralipid if refractory to standard resuscitation efforts
- Initial bolus of intralipid 20% at 1.5 cc/kg with a infusion of 0.25 mL/kg/min for 30-60 minutes.
- A bolus can be repeated 1 - 2 times for persistent asystole
What is the presentation of a subdural block?
- Uneventful epidural identification and catheter insertion
- Sensory change over 10 - 2- minutes
- Excessive spread for volume injected
- High cephalad spread with poor caudal spread and sacral sparing
- Asymmetric distribution
- Minimal or moderate motor block
- Minimal or easily controlled hypotension
Where does a subdural block occur?
Between the dura and arachnoid mater
T/F: Horner’s Syndrome can be seen in a subdural block?
True
