2 What hematologic changes accompany pregnancy?

Table 59-2 summarizes the hematologic changes of pregnancy. Plasma volume increases from 40 to 70 ml/kg near term, and blood volume increases by 1000 to 1500 ml. The relative anemia of pregnancy is caused by a relatively slower rise in red blood cell mass compared to plasma volume. Maternal anemia, usually the result of iron deficiency, occurs when the hemoglobin falls below 10 g or the hematocrit is <30%.

TABLE 59-2 Hematologic Changes of Pregnancy

PTT, Partial thromboplastin time; PT, prothrombin time.

Pregnancy is associated with an increase in platelet activation and consumption and most coagulation factors. Because of this, parturients are hypercoagulable and at risk for thrombotic events (such as deep vein thrombosis and pulmonary embolism). The increase in platelet consumption is compensated for by an increase in platelet production; therefore, the platelet count is usually normal. Thrombocytopenia can occur in 0.9% of normal patients, although it is often associated with preeclampsia or hemolysis, elevated liver enzymes, and low platelet count (HELLP) syndrome. The prothrombin time and partial thromboplastin times are shortened.

3 What pulmonary and respiratory changes occur with pregnancy?

Table 59-3 summarizes the respiratory changes of pregnancy. Pregnancy leads to capillary engorgement and edema of the respiratory tract. The mucosa also becomes friable, which may lead to bleeding with manipulation or trauma. These changes in the airway and the enlarged breasts of the pregnant patient make laryngoscopy difficult. Adding to the problem, the increased oxygen consumption and decreased functional residual capacity (FRC) make the laboring patient more prone to hypoxia and rapid desaturation during apneic periods.

TABLE 59-3 Respiratory Changes at Term in Pregnancy

FEV₁, Forced expiratory volume in 1 second.

4 What is a normal arterial blood gas in a pregnant patient?

See Table 59-4.

5 What gastrointestinal changes occur during pregnancy?

The upward displacement of the stomach by the expanding uterus shifts the gastroesophageal junction. This decreases the tone of the lower esophageal sphincter and predisposes the pregnant patient to reflux. The gravid uterus also increases intragastric pressure. These in combination make the parturient prone to regurgitation and aspiration. Gastric motility and emptying time can be prolonged, and the pregnant patient is always considered to have a full stomach. Standard preoperative aspiration prophylaxis includes metoclopramide, an H₂-blocker, and a nonparticulate antacid.

6 What renal changes are associated with pregnancy?

Renal plasma flow, glomerular filtration rate, and creatinine clearance increase by the fourth month of gestation. Blood urea nitrogen (BUN) and creatinine are decreased; normal values in pregnancy are 6 to 9 and 0.4 to 0.6 mg/dl, respectively. Glucosuria up to 10 g/dl and proteinuria up to 300 mg/dl are not abnormal. Anatomically the renal calyces, pelves, and ureters dilate beginning around 12 weeks’ gestation. Urinary stasis contributes to the frequency of urinary tract infections seen in pregnancy.

7 What changes occur in the central nervous system of pregnant patients?

Progesterone in both the plasma and cerebrospinal fluid increases tenfold to twentyfold in late pregnancy. Progesterone is sedating and potentiates the effects of volatile anesthetics. Pregnant patients are also more sensitive to local anesthetics.

8 What hepatic alterations occur with pregnancy?

Liver size, blood flow, and liver morphology do not change during pregnancy. Lactate dehydrogenase, serum bilirubin, alanine aminotransferase, aspartate aminotransferase, and alkaline phosphatase (of placental origin) increase with pregnancy. Gallbladder emptying is slowed during pregnancy, and the bile tends to be concentrated, predisposing the pregnant patient to gallstone formation.