1 What are normal arterial blood gas findings in pregnancy?

Pregnancy results in increased ventilation because of elevated carbon dioxide production, as well as an increase in respiratory drive mediated largely by progesterone. These changes cause a low arterial partial pressure of carbon dioxide, at about 30 mm Hg by term. Plasma bicarbonate is decreased to 18 to 21 mEq/L, maintaining the arterial pH in the range of 7.40 to 7.45. Alveolar to arterial oxygen tension difference is usually unchanged, and the mean arterial PO₂ is generally about 100 mm Hg.

2 How does pregnancy affect hemodynamics?

Cardiovascular physiology changes significantly during pregnancy, characterized by an increase in blood volume, an elevation in cardiac output, and a small decrease in blood pressure, resulting in a number of changes in the normal hemodynamic values in the third trimester (Table 83-1). In the supine position, the gravid uterus may produce significant mechanical obstruction of the inferior vena cava, reducing venous return and resulting in a decrease in cardiac output and hypotension. Maternal syncope or fetal distress may result. Supine hypotension syndrome may be avoided by positioning the patient on her left side, or at least with the right hip slightly elevated.

^{Table 83-1} Effect of Late Pregnancy on Pulmonary Artery Catheter Measurements

3 What factors affect oxygen delivery to the fetus?

Oxygen delivery to the fetus is determined by the maternal arterial oxygen content, uterine blood flow, and placental function. A number of factors may adversely affect blood flow to the uteroplacental vasculature, which is normally maximally vasodilated. A decrease in maternal cardiac output reduces fetal oxygenation. The maternal response to hypotension does not favor the uterus, and catecholamines (endogenous or exogenous) may aggravate fetal hypoxia by producing uterine vasoconstriction. Uterine blood flow may also be reduced by maternal alkalosis and during uterine contractions.

4 Are there any special concerns to be considered when inserting an endotracheal tube in a critically ill pregnant patient?

The upper airway in pregnancy may be edematous and friable because of the effects of estrogen and aggravated in the presence of preeclampsia because of excessive edema. The nasal route should be avoided, and a smaller endotracheal tube may be necessary. Because of the reduced functional residual capacity and increased oxygen consumption, hypoxemia will develop in a pregnant woman more rapidly than in nonpregnant, critically ill patients during intubation. Intubation should be carried out by the most skilled person available.

Note: The incidence of failed intubation is eight times higher in the obstetric population than in nonobstetric patients.

5 Describe the principles of management of severe preeclampsia

The most important aspect of management is the well-timed delivery of the fetus. Supportive treatment involves fluid management, control of hypertension, and prevention of seizures:

6 What are the clinical features of the HELLP syndrome?

The HELLP syndrome (i.e., hemolysis, elevated liver enzyme levels, and low platelet count) is a complication of preeclampsia characterized by multiorgan dysfunction. The diagnostic features are the presence of thrombocytopenia, elevated liver enzymes, and a microangiopathic hemolytic anemia. The patient may present with epigastric or right upper quadrant pain, nausea, and vomiting, with or without other features of preeclampsia. Significant hemorrhage may result from the thrombocytopenia. A rare but catastrophic consequence of HELLP syndrome is hepatic hemorrhage, manifesting with sudden shock or acute abdominal pain.

7 What is acute fatty liver of pregnancy?

This is an uncommon complication of pregnancy manifesting with acute fulminant hepatic failure during the third trimester. Increased awareness of this condition has resulted in earlier diagnosis, with milder liver disease and an improved outcome. The clinical presentation is with malaise, anorexia, and vomiting, followed by abdominal pain and jaundice. The patient deteriorates rapidly with acute liver failure manifested by coagulopathy, hemorrhage, renal failure, and encephalopathy. Management requires urgent delivery of the fetus and supportive therapy for fulminant hepatic failure.

8 How does amniotic fluid embolism present?

Amniotic fluid embolism is a rare but catastrophic obstetric complication usually associated with labor, delivery, or other uterine manipulations. The typical presentation is a sudden onset of severe dyspnea, hypoxemia, and cardiovascular collapse, which may be accompanied by seizures. The maternal presentation is accompanied or preceded by sudden fetal distress. A significant portion of patients die acutely within the first hour. Survivors commonly have a disseminated intravascular coagulopathy and acute respiratory distress syndrome. Management is supportive, and the prognosis for mother and fetus is poor.