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
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 ||Download (.pdf)
Table 53-1. Summary of Physiologic Changes of Pregnancy at Term
|Total blood volume||Increase||25–40%|
|Serum cholinesterase activity||Decrease||20–30%|
|Functional residual capacity||Decrease||20%|
|Arterial carbon dioxide tension||Decrease||10 mm Hg|
|Arterial oxygen tension||Increase||10 mm Hg|
|Minimum alveolar concentration||Decrease||32–40%|
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.
|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
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 ...