Chapter 105

• Understanding the normal physiology of pregnancy is essential to evaluate the adequacy of cardiopulmonary function in the critically ill gravid woman.
• Pregnancy results in an increased cardiac output, which in late pregnancy may be diminished in the supine position by vena caval compression from the enlarged uterus.
• The reduced functional residual capacity (FRC) and increased oxygen consumption noted in normal pregnancy increase the risk of hypoxemia during intubation or hypoventilation.
• Hyperventilation during pregnancy results in a primary respiratory alkalosis and a compensatory metabolic acidosis with the following typical arterial blood gas values: PO2 >100 mm Hg, PCO2 27 to 32 mm Hg, and serum bicarbonate concentration 18 to 21 mEq/L.
• Fetal viability depends on adequate oxygen delivery. As a result of the dilutional anemia of pregnancy, cardiac output becomes the critical determinant of fetal oxygen delivery and must be maintained.
• Hemorrhage in pregnancy may be massive and require extraordinary fluid resuscitation.
• Vasoactive drugs should be used with caution in the pregnant patient, since they may reduce uterine blood flow.
• Control of increased afterload may require intravenous agents: Sodium nitroprusside should be used only for imminently life-threatening conditions, since cyanide toxicity may result in fetal injury or demise. Nicardipine is an intravenous calcium channel blocker that is preferable to nitroprusside, and experience with labetalol, a combined alpha-beta blocker, is growing and promising.
• Preeclampsia is a multisystem disorder characterized by hypertension, central nervous system dysfunction, coagulopathy, pulmonary edema, renal failure, and liver function abnormalities.
• Cardiopulmonary resuscitation must be modified in pregnancy and includes emergent cesarean section in selected patients.
• Pregnancy may represent a state of increased risk of pulmonary edema formation; acute hypoxemic respiratory failure is most often due to tocolytic therapy, and if due to tocolytics, usually resolves with supportive care.
• Successful management of critical illness in pregnancy requires continuous integration of the intensive care team with obstetric and neonatal consultants; mechanisms should exist for emergent involvement of the appropriate personnel.

Pregnancy greatly complicates critical illness, since assessment, monitoring, and treatment must take into account both maternal and fetal well-being. Knowledge of the normal changes in maternal respiratory, cardiac, and acid-base physiology in pregnancy is essential to distinguish between adaptive and pathologic changes.

This chapter begins with an overview of the changes in cardiovascular, respiratory, renal, and gastrointestinal physiology in normal pregnancy. Next, the determinants of fetal oxygen delivery are reviewed. The remainder of the chapter focuses on the disorders that can result in critical illness in pregnancy and the appropriate management of each. Finally, the importance of acid-base homeostasis, prophylaxis to prevent gastrointestinal bleeding, and early nutrition are discussed.

In many ways our understanding of the complex interaction between disease state and maternal/fetal physiology is incomplete. Thus we rely on an approach that assumes that measures that optimize maternal well-being are usually best for the fetus as well. Nonetheless, throughout critical illness, monitoring and management decisions must take into account fetal as well as ...

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