Page 1785 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

1254 PART 11: Special Problems in Critical Care

CHAPTER Critical Illness in Pregnancy
stress of surgery may make vaginal delivery a better option in the
127 Karen C. Patterson • The increased volume of distribution and glomerular filtration rate
nonemergent setting and when the mother is capable of labor.
Michael F. O’Connor
Jesse B. Hall may affect dosing of medications in pregnancy.
Mary E. Strek • Successful management of critical illness in pregnancy requires a
multidisciplinary team of intensive care, pharmacy, obstetric, and
neonatal consultants.
KEY POINTS

• Assessment of the adequacy of maternal blood flow requires an
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understanding that the baseline flow is substantially increased and Critical illness during pregnancy requires a multidisciplinary approach that
is further augmented during labor and delivery. considers both the mother and the fetus. There is a paucity of definitive tri-
• The increased cardiac output of pregnancy is often diminished, als to guide therapy in critically ill pregnant patients. Measures that optimize
maternal well-being are usually best for the fetus as well. Knowledge of
especially in late pregnancy, in the supine position by uterine com- the expected adaptations in maternal physiology is essential to distinguish
pression of the vena cava and abdominal aorta. Placing the patient between normal and pathologic findings in gravid patients. This chapter
in the left lateral decubitus position is an important management begins with an overview of the normal physiologic changes in pregnancy
principle in shock. and the determinants of fetal oxygen delivery. The remainder of the chapter
• The normal hyperventilation of pregnancy results in a respiratory focuses on the disorders and management of critical illness in pregnancy.
alkalosis with a compensatory metabolic acidosis. The normal
> 100 mm Hg,
arterial blood gas values in pregnancy include a P O 2 PHYSIOLOGY OF PREGNANCY
of 27 to 34 mm Hg, and a serum bicarbonate concentration
a P CO 2
of 18 to 21 mEq/L. ■ ADAPTATION OF THE CIRCULATORY SYSTEM
• Fetal viability depends on adequate oxygen delivery. Maternal car- In pregnancy, numerous circulatory adjustments occur that ensure
diac output is the critical determinant of placental blood flow and adequate oxygen delivery to the fetus (Table 127-1). Maternal blood
1
fetal oxygen delivery. Diminished placental blood flow is particu- volume increases early in pregnancy, reaching a level approximately 40%
larly dangerous if superimposed on maternal anemia or hypoxemia. above baseline by the third trimester. This increase is due to a 20% to
1-3
Fetal oxygen delivery can be improved by optimizing maternal car- 40% increase in the number of erythrocytes and a 40% to 50% increase
diac function, transfusing blood to increase oxygen carrying capacity, in plasma volume; the magnitude of the increase in blood volume is
and providing supplemental oxygen. even greater with multiple gestations. As the increase in plasma volume
• In critically ill gravidas, fetal monitoring should be performed is greater than the increase in erythrocytes, a mild dilutional anemia
when available and in collaboration with obstetrics clinicians. results, with an approximate 12% decrease in hematocrit. Extracellular
2
Changes in fetal heart rate can be a sign of inadequate oxygen volume expansion is also associated with a decreased serum albumin
delivery. In addition to fetal heart rate monitoring, the parameters concentration and colloid osmotic pressure; both indices reach a nadir at
of oxygen delivery and acid-base status in the mother are generally 26 weeks, although there is a further decline in colloid osmotic pressure
the best measures of the adequacy of oxygen delivery to the fetus. in the immediate postpartum period. Extracellular volume expansion is
3
• Hemorrhage in pregnancy can be massive and may require mediated by sodium retention from increased aldosterone production,
extraordinary fluid resuscitation, blood product replacement, and which results in mild peripheral edema in most pregnancies. 2,3
early surgical consultation. Coincident with increased blood volume is a 30% to 50% increase
• In pregnancy, sepsis is rare but can be severe. Source control and in cardiac output. This begins in the first trimester and continues
early surgical evaluation for obstetric infections are essential. throughout gestation as heart rate, and to a lesser degree stroke volume,
4-6
Vasoactive drugs may be indicated in refractory hypotension to increase. The increased heart rate reaches a maximum of 15 to 20
5,7
preserve maternal cardiac output and fetal oxygen delivery. beats per minute above resting nonpregnant levels by weeks 32 to 36.
Increased stroke volume occurs early, and is due to increased preload
• Preeclampsia is a multisystem disorder of vascular dysfunction from augmented blood volume, and to decreased afterload from a 20%
characterized by hypertension and proteinuria. Central ner- to 30% fall in systemic vascular resistance (SVR). The fall in SVR is
vous system dysfunction, coagulopathy, pulmonary edema, renal attributed to flow through the low-resistance uteroplacental bed and
dysfunction, and liver function abnormalities may occur. Early to hormone-mediated vasodilation. During labor, cardiac output can
recognition and well-timed delivery are crucial.
• When severe or when associated with preeclampsia, treatment of
hypertension in pregnancy may require intravenous agents: labet- TABLE 127-1 Circulatory Changes in Pregnancy
alol and hydralazine are preferable to nitroprusside. Parameter Change Time Course
• Cardiopulmonary resuscitation in pregnancy includes consideration, Maternal blood volume Increase 40% Peak at 34 weeks
when feasible, of emergent cesarean section in selected patients. Red cell mass Increase <20%-40% Peak at 40 weeks
• In evolving respiratory failure, early elective intubation and
mechanical ventilation are recommended to gain airway access in Hematocrit Decrease 12% Nadir at 30 weeks
a controlled setting and to avoid respiratory crisis. Heart rate Increase 10%-30% (15-20 bpm) Peak at 32-36 weeks
• The reduced functional residual capacity (FRC) and increased Stroke volume Increases Increases throughout
oxygen consumption in pregnancy increase the risk of hypoxemia Cardiac output Increases 30%-50% Peak at 25-32 weeks
during intubation or hypoventilation. Blood pressure Decreases 10%-20% Nadir at 28 weeks
• Decisions regarding labor and delivery are important management
issues. Cesarean section is a more controlled mode of delivery. Systemic vascular resistance Decreases 20%-30% 1st trimester
However, even with adequate sedation and analgesia, the physiologic Pulmonary vascular resistance Decreases 20%-30% 1st trimester
bpm, beats per minute.

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