Quiz 2 Flashcards
1st stage – pain source is mainly _________ segment from contractions (_____ dermatomes)
lower uterine
T10-L1
2nd stage – source is __________ via ____________ (_____ dermatomes)
perineal structures
pudendal nerve
S2-S4
Meperidine (Demerol)
- Dose 25-50 mg IV.
- Onset 5 min.
- Kinetics Half-life 18-23 hrs in neonate, also has active metabolites.
- Causes frequent N/V.
- Neonatal respiratory depression unlikely if given less than 1 hour prior to delivery.
- Contraindicated in pt with seizure d/o or renal failure.
Nalbuphine (Nubain)
- Mu opioid antagonist, kappa agonist.
- Has ceiling effect on resp depression but no real large difference in side effects.
- Dysphoria common.
- Used to treat opioid induced pruritis (5-10 mg iv q 6 H prn)
Butorphanol (Stadol)
- Dose 1-2 mg.
- Some reports suggest better analgesic profile than fentanyl.
- Sedation common.
- Ceiling effect on resp depression.
dose limit on volatile anesthetics?
0.5 MAC
Paracervical block
- 1st stage of labor.
- Technique: 5cc of local injected submucosally at 3 and 9 o’clock position beside cervix.
Pudendal block
- Used for 2nd stage of labor.
- Good for certain patients with contraindication for neuraxial block.
- Technique: Needle is placed bilaterally via transvaginal approach under the ischial spines.
Local anesthetics: Esters
- Ester derivatives of para-aminobenzoic acid (PABA).
- Metabolized by plasma cholinesterase.
- Metabolite PABA is a known allergen.
Local anesthetics: Amides
- Amide linkage, metabolized by liver.
- No PABA -> allergic reactions are rare.
Local anesthetics: Lipid Solubility
- Influences potency – more lipid soluble agents can pass more easily through the lipoprotein nerve membrane.
- Increasing lipid solubility enhances placental diffusion.
Local anesthetics: Protein Binding
- Influences duration – increased protein binding correlates to longer duration.
- High protein binding decreases placental transfer.
- Α1-acid glycoprotein (high affinity, low capacity)
- Albumin (low affinity, high capacity)
Local anesthetic site of action is ___________________ sodium channel
neuronal cell membrane
The closer pKa is to physiological pH -> more LA in nonpolar form -> ______ onset
faster
Artificially raise pH so it is closer to pKa -> add __________
bicarbonate
Temperature affects onset, with warmed LA ________ onset time
reduces
Increasing doses of LA ->_____ onset, ______ duration
faster
longer
Pain receptors
A-delta
C fibers
LA For labor epidural analgesia:
- Bupivacaine
- Ropivacaine
- Lidocaine
LA For operative epidural anesthesia
- Lidocaine
- 2-chloroprocaine
LA For spinal anesthesia
- Tetracaine
- Bupivacaine
2-Chloroprocaine
Dose:
15-25cc of 3% 2-chloroprocaine for epidural c-section (may require re-dosing, give 5cc at a time.
Properties
- The only ester local used in epidural space
- Rapid onset, very short duration
- Lot of motor block
- Low risk of toxicity, very rapidly metabolized in blood by pseudocholinesterase
Bupivacaine
Dose for labor epidural:
initial bolus 15-20 mg (e.g., 7.5-10 cc 0.2% bupivacaine), infusion- 8-12 mg/hr (e.g., 8-12 cc/hr of 0.1% solution).
- Long duration, less motor block than most other agents.
- Produces refractory v-tach/v-fib if large IV dose given.
Levobupivacaine:
- L-isomer of bupivacaine
- Less cardiotoxic
Ropivacaine:
- Less cardiotoxicity than even levo in animal studies.
- May be about 25% less potent than bupivacaine.
- Not approved for spinal (neither is levo).
For obstetrics lumbar level is best to cover __________ dermatomes
T-10 thru S4
Contraindications to neuraxial blockade
- patient refusal
- Infection at the site of injection.
- Coagulopathy (liver failure, anticoagulants, HELLP syndrome, thrombocytopenia etc.).
- Intracranial mass lesion.
- Aortic stenosis.
- Existing spinal or neurological pathology.
- Hemodyamic instability
Epidural space on avg identified ____ cm deep
4.75
Local Anesthetic Toxicity - CNS
Tinnitus Light-headedness Metallic taste Circumoral numbness Convulsions Loss of consciousness Respiratory arrest
Increased ______ and _______ lower seizure threshold
PaCO2
acidosis
(Acidosis decreases protein binding -> more free LA)
Local Anesthetic Toxicity - CVS
- Inhibition of cardiac sodium channels.
- Decrease 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.
Intrallipid dosing for LAST
- 1.5 mL/kg as an initial bolus, followed by
- 0.25 mL/kg/min for 30-60 minutes
- Bolus could be repeated1-2 times for persistent asystole
- Infusion rate could be increasedif the BP declines
Preterm labor
regular uterine contractions occurring at least q10 min resulting in cervical change prior to 37 weeks
Low birth weight (LBW)
Very low birth weight (VLBW)
any infant < 2500g at birth
any infant < 1500g
Survival can increase ____ each DAY btw 25-26 wks
~5%
C-section is proven safer in PTL with _____ presentation
breech
Tocolytic Therapy criteria
Gestational age 20-34 wks, EFW < 2500 g, absence of fetal distress
Tocolytic Therapy: Methylxanthines
- Aminophylline
- Phosphodiesterase – increase intracellular cAMP -> uterine muscle relaxation.
Narrow therapeutic margin and frequent toxic side effects limit clinical use.
Tocolytic Therapy: Calcium Channel Blockers
-Nifedipine
Myometrium contractility related to free calcium concentration: dec.Ca2+ -> dec. contractility.
Maternal side effects:
-Hypotension, tachycardia, dizziness, palpitations
-Facial flushing
-Vasodilation, peripheral edema
-Myocardial depression, conduction defects
-Hepatic dysfunction
-Postpartum hemorrhage
-Fetal side effects
-Decreased UBF -> fetal hypoxemia and fetal acidosis
Tocolytic Therapy: Prostaglandin Synthetase Inhibitors
-Indomethacin, Sulindac
-Mechanism of action: dec. cyclooxygenase -> dec. prostaglandin
Maternal side effects:
-Nausea
-Heartburn
-Transient dec. platelet aggregation -> bleeding
-Primary pulmonary HTN
Fetal side effects:
-Crosses placenta
-Premature closure of ductus arteriosus
-Persistent fetal circulation
-Renal impairment, transient oliguria
Magnesium treatment ranges, treatment for toxicity?
Normal treatment range is 4-7 mg/100 mL
Toxicity at greater values:
- 8-10 = loss of deep tendon reflexes
- 10-15 = respiratory depression, cardiac conduction defects (wide QRS, inc P-R interval)
- 20+ = cardiac arrest
Tx: calcium gluconate or CaCl
Tocolytic Therapy: Beta adrenergic agonists
Terbutaline, Ritodrine
Direct stimulation of β-adrenergic receptors in uterine smooth muscle -> inc. cAMP -> uterine relaxation
Risk factors for Beta adrenergic agonist Pulmonary Edema
- Increased IVF administration
- Multiple gestation
- Tocolysis greater than 24 hrs
- Concomitant magnesium therapy
- Infection
- Hypokalemia
- Undiagnosed heart disease
Review slide 21-24 on OB4
.
Signs and Symptoms of uterine rupture, most reliable sign?
- Sudden abdominal pain despite functioning epidural
- Vaginal bleeding
- Hypotension
- Cessation of labor
- Fetal distress – most reliable sign
Increases risk of uterine rupture
- Previous uterine surgery
- Trauma
- Multiparity
- Uterine anomaly
- Oxytocin
- Placenta percreta
- Tumors
- Macrosomia
- Malposition
Greatest chance of uncomplicated spontaneous vaginal delivery with:
vertex presentation, flexed c-spine (chin to chest), occiput anterior (face down).
Post-Maturity complications
- Dec. uteroplacental blood flow fetal distress
- Umbilical cord compression due to oligohydramnios
- Meconium staining of amniotic fluid
- Inc. incidence of macrosomia, shoulder dystocia
Intrauterine Fetal Demise (IUFD) Causes
- Chromosomal abnormalities
- Congenital malformations
- Multiple gestation
- Infection
- Cord accidents
- Placental factors
- Maternal immunological or thyroid disease
- Isoimmunization
- Maternal trauma
Umbilical cord length concerns
<30 cm risks compression, constriction, rupture.
>72 cm risks cord entanglement
