Chapter 40. Obstetric Regional Anesthesia
All of the following are normal physiologic changes of pregnancy except:
A. Minute ventilation increased by 50%
B. Total blood volume increased by 40%
C. Functional residual capacity (FRC) decreased by 30%
D. Tidal volume decreased by 25%
D is not a normal physiologic change, so option D is correct. Tidal volume increases 40%.
A is a normal physiologic change, so option A is incorrect. Minute ventilation increases up to 50% of normal in parturients by term. This increase is due primarily to increases in tidal volume up to 40% and a lesser increase in respiratory rate.
B is a normal physiologic change, so option B is incorrect. Total blood volume increases by up to 40% by term and partially accounts for increased cardiac output along with increased HR.
C is a normal physiologic change, so option C is incorrect. Due to an enlarged uterus elevating the diaphragm, FRC decreases.
Which statement is true regarding anesthetic requirements in the parturient patient?
A. Lower doses of local anesthetics are required due to estrogen-mediated increased neural sensitivity.
B. The minimum alveolar concentration (MAC) for inhalational agents is increased.
C. Epidural venous engorgement has no effect on subarachnoid spread of local anesthetics in parturients.
D. Overall, lower doses of local anesthetics are needed per dermatomal segment in pregnant patients.
D is correct. Due to progesterone-mediated increase neural sensitivity and greater spread of local anesthetic in epidural and subarachnoid space, smaller doses of local anesthetic are needed for epidural and spinal blocks for pregnant patients.
A is incorrect. Increased neural sensitivity during pregnancy is progesterone-mediated, not estrogen-mediated. Levels of both hormones increase steadily throughout pregnancy.
B is incorrect. MAC is decreased in parturients starting at 8–12 weeks gestation and is thought to be progesterone-related.
C is incorrect. Spread of local anesthetic in both epidural and subarachnoid spaces is enhanced due to epidural venous engorgement.
Which statement is true regarding placental transfer of local anesthetics to the fetus?
A. The nonionized forms of local anesthetics are better able to cross the placenta into the fetus.
B. Acidosis in the mother increases ion trapping of local anesthetic in the fetus.
C. Due to lack of systemic uptake, ...