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