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Chapter 53. Obstetric Regional Anesthesia

Philippe Gautier, MD; Edward Jew, MD; Bonnie Deschner, MD; Alan C. Santos, MD

Most women experience moderate to severe pain during labor and delivery, often requiring some form of pharmacologic analgesia.1 The lack of proper psychological preparation combined with fear and anxiety can greatly enhance the patient's sensitivity to pain and further add to the discomfort during labor and delivery. However, skillfully conducted obstetric analgesia, in addition to relieving pain and anxiety, may benefit the mother in many other ways. This chapter focuses on management of an obstetric patient with primary focus on regional anesthesia techniques.

Physiologic Changes of Pregnancy

Pregnancy results in significant changes affecting most maternal organ systems (Table 53–1). These changes are initiated by hormones secreted by the corpus luteum and the placenta. Such changes have important implications for the anesthesiologist caring for the pregnant patient. This chapter reviews the most relevant physiologic changes of pregnancy and discusses the approach to obstetric management using regional anesthesia.

Table 53-1. Summary of Physiologic Changes of Pregnancy at Term
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Table 53-1. Summary of Physiologic Changes of Pregnancy at Term
VariableChangeAmount
Total blood volumeIncrease25–40%
Plasma volumeIncrease40–50%
FibrinogenIncrease50%
Serum cholinesterase activityDecrease20–30%
Cardiac outputIncrease30–50%
Minute ventilationIncrease50%
Alveolar ventilationIncrease70%
Functional residual capacityDecrease20%
Oxygen consumptionIncrease20%
Arterial carbon dioxide tensionDecrease10 mm Hg
Arterial oxygen tensionIncrease10 mm Hg
Minimum alveolar concentrationDecrease32–40%

Changes in the Cardiovascular System

Oxygen consumption increases during pregnancy, requiring the maternal cardiovascular system to meet the increasing metabolic demands of a growing fetus. The end result of these changes is an increase in heart rate (15–25%) and cardiac output (up to 50%) compared with values before pregnancy. In addition, lower vascular resistance is found in the uterine, renal, and other vascular beds. These changes result in a lower arterial blood pressure because of a decrease in peripheral resistance, which exceeds the increase in cardiac output. Decreased vascular resistance is mostly due to the secretion of estrogens, progesterone, and prostacyclin.2 Particularly significant increase in cardiac output occurs during labor and in the immediate postpartum period owing to added blood volume from the contracted uterus.

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Clinical Pearls
Cardiovascular changes and pitfalls in advanced pregnancy are:
  • Increase in heart rate (15–25%) and cardiac output (up to 50%).
  • Decrease in vascular resistance in the uterine, renal, and other vascular beds.
  • Compression of the lower aorta in the supine position may further decrease uteroplacental perfusion and result in fetal asphyxia.
  • For the above reason, significant hypotension is more likely to occur in the pregnant than in the nonpregnant woman having regional anesthesia, necessitating uterine displacement or lateral pelvic tilt maneuvers, intravascular preloading, and ready availability of vasopressors.

From the second trimester, aortocaval compression by the enlarged uterus becomes progressively ...

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