Hemodynamics

Many profound physiologic changes occur in the cardiovascular system during pregnancy. Blood volume expands by 30% to 40%. The expanded blood volume during pregnancy and the direct ionotropic effects of estrogen lead to an increased heart rate and stroke volume (19). Heart rate begins to increase at the fifth week of gestation and continues to rise until the 32nd week, at which time it is approximately 15% above non-pregnant values. Cardiac output increases by 30% to 50% at the end of the second

TABLE1 ■ Normal Maternal Physiologic and Biochemical Changes

System

Increased

Decreased

Cardiovascular

Blood volume

Peripheral vascular resistance

Cardiac output

Lower extremity

venous pressure

Respiratory

Minute ventilation

Functional residual capacity

Total lung capacity

Gastrointestinal/

Alkaline phosphatase

Gastric, small intestine,

Hepatobiliary

colonic motility

Portal venous pressure

Gallbladder emptying

Bile cholesterol saturation

Albumin

Hematologic

Red blood cell mass

Hematocrit

White blood cells

Platelets

Factors VII, VIII, X, XII,

fibrinogen

Renal

Glomerular filtration rate

Blood-urea-nitrogen

Oreatinine clearance

Serum Cr

Renin

Sodium

Endocrine

Aldosterone

Free cortisol

Source: From Refs. 19, 20,25,26, 28,31,34.

FIGURE 1 ■ Fundal height by gestational age in weeks. Source: From Ref. 139.

FIGURE2 ■ Trocar placement for laparoscopic appendectomy changes by size of gravid uterus. Numbers indicate the order of insertion.

FIGURE2 ■ Trocar placement for laparoscopic appendectomy changes by size of gravid uterus. Numbers indicate the order of insertion.

trimester with most of the increased cardiac output directed to the uterus and placenta. Maternal position largely affects cardiac output later in pregnancy. When lying in the supine position, the enlarged uterus compresses the inferior vena cava leading to a decrease in venous return and thereby a decrease in cardiac output (20). Compared to the lateral recumbent position, patients lying supine may experience a 10% to 30% decrease in cardiac output (21,22).

In nonpregnant patients, a 25% decrease in cardiac index is seen with induction of anesthesia with a further decrease to 50% normal after CO2 insufflation and an increase in mean arterial pressure and systemic vascular resistance (23). A recent study from the Brigham and Women's Hospital demonstrated these same hemodynamic changes in pregnant patients undergoing laparoscopic surgery (24). There was no exaggerated cardiovascular response to CO2 pneumoperitoneum during pregnancy as some have speculated might occur.

The upward displacement of the diaphragm is increased by CO2 pneumoperitoneum. This has led to the recommendation that intra-abdominal pressures should be minimized during laparoscopic surgery with pressures less than 12mmHg.

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