Obstetric Anesthesia Flashcards
Are pregnant patients more or less sensitive to local anesthetics?
more sensitive
What is a normal ABG in pregnancy?
pH: 7.45 (mild alkalosis)
PaCO2: 30-32 (mild hypocarbia)
PaO2: normal
bicarb: 19 (mildly decreased)
Why is the maternal oxygen-hemoglobin disociation curve shifted to the right during pregnancy?
increased 2,3-DPG production
Why is the fetal oxygen-hemoglobin disociation curve shifted to the left?
inability to bind 2,3-DPG
Why are tidal volumes larger as pregnancy progresses?
increased A/P diameter of the chest
What is a typical oxygen tension in the placenta?
40 mmHg
Why don’t muscle relaxants cross the placenta?
They are large, charged, and hydrophilic
Why are most local anesthetics found in higher concentrations in the fetus than in the mother when delivered IV?
lower pH in the fetus protonates local anesthetics after they cross the placenta, ion trapping them in the fetus
Why is chloroprocaine NOT found in higher concentrations in the fetus after IV administration to the mother?
rapid metabolism by plasma esterases in the maternal circulation
Why are bupivacaine and ropivacaine NOT found in higher concentration in the fetus after IV administration to the mother?
high protein binding, limited placental transfer
What are the side effects of terbutaline used as a tocolytic?
tachycardia (ß1 agonist)
hypokalemia (ß2 agonist)
What are the signs of magnesium toxicity?
muscle weakness and loss of deep tendon reflexes
sedation
SA and AV nodal blockade leading to cardiac arrest
What are the theoretical concerns with ketorolac given for labor pain?
ductus arteriosus closure
tocolysis
increased bleeding
What is the mortality rate in parturients with Eisenmenger’s syndrome?
30-50%
Why should a sympathectomy during neuraxial anesthesia be avoided in patients with Eisenmenger’s syndrome?
Decreasing LV preload and afterload with a sympathectomy will worsen the R to L shunt and cause cyanosis.
Why should meperidine be avoided in patients with Eisenmenger’s syndrome?
Its weak local anesthetic properties could cause a sympathectomy
Is neuraxial anesthesia safe and effective in patient’s with idiopathic intracranial hypertension?
Yes
Why should nitrous oxide be avoided prior to delivery in a C-section under GA?
diffusion hypoxia of the newborn
*In breathing off nitrous oxide, it will diffuse from the fetal blood to the alveoli faster than O2 or CO2, filling the alveoli and causing hypoxia*
What is a normal fetal scalp pH?
> 7.25
What causes early decelerations?
increased fetal vagal tone in response to head compression
What is the most common cause of mortality in pre-eclampsia?
cerebral hemorrhage
What are the likely mechanisms of magnesium in preventing eclampsia?
calcium inhibition
NMDA receptor blockade
How should magnesium toxicity be treated?
calcium
What are the risk factors for placenta previa?
prior c-section
prior uterine surgery
multiparity
advance maternal age
What are the risk factors for uterine rupture?
prior c-section
prior myomectomy
excess oxytocin
forceps delivery
How is ACLS different in a pregnant patient?
manual left uterine displacement should be maintained
a viable fetus should be delivered within the first 4 minutes as irreversible neurologic injury begins around 5 minutes
compressions are performed slightly higher in the chest
When should semi-elective surgery be performed during pregnancy? Why?
2nd trimester
*High risk of spontaneous abortion in the 1st trimester, and high risk of preterm labor in the 3rd trimester*
What is the association between benzodiazepines and cleft palate?
Possible increase in babies whose mothers were taking chronic benzodiazepines during the first trimester (conflicting data)
