TABLE 44-1 Physiologic Changes in Pregnancy | |||||||||||||||||||||||||||||||||||||||||||||
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TABLE 44-2 Causes of Respiratory Failure in Pregnancy | |
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Acute Respiratory Failure in Pregnancy
Acute Respiratory Failure in Pregnancy
Mitra Ghasemi
Oren P. Schaefer
I. GENERAL PRINCIPLES
A. Acute respiratory failure is an important cause of maternal and fetal morbidity and mortality.
B. An understanding of normal physiologic changes in pregnancy is important in considering pathophysiology (see Table 44-1).
II. ETIOLOGY
Table 44-2 lists the most important causes of respiratory failure in pregnancy.
A. Thromboembolic disease.
1. Pulmonary thromboembolism: leading cause of maternal mortality in developed world and the second most common cause of mortality (after bleeding) in developing world.
2. Increased risk in pregnancy is an example of Virchow’s triad.
a. Hypercoagulability (increases in coagulation factor V, decreased anticoagulant and fibrinolytic activity).
b. Venous stasis (progesterone-induced venodilation, pelvic venous compression by the gravid uterus, and pulsatile compression of the left iliac vein by the right iliac artery).
c. Vascular damage (vascular compression at spontaneous, operative, or assisted delivery).
3. Risks in addition to usual risk factors for venous thromboembolism (VTE) in general population: increased maternal age, multiparity, obesity, assisted reproduction, postpartum hemorrhage, or preeclampsia.
4. Challenges in diagnosis of VTE in pregnancy.
a. Symptoms of VTE mimic the physiologic changes of pregnancy (dyspnea, tachycardia, and leg swelling).
b. D-dimer concentration rises gradually during pregnancy and only returns to normal levels after 4 to 6 weeks postpartum.
c. Potential oncogenic and teratogenic risk incurred due to fetal exposure to diagnostic radiation.
d. Compression ultrasonography in pregnant patients with suspected pulmonary embolism (PE) without leg symptoms is associated with an increased likelihood of false-negative results (due to a higher risk of isolated pelvic deep venous thrombosis) and the potential for falsepositive findings related to the slow venous flow in pregnancy.
e. Ventilation perfusion scintigraphy: Advantages are the lower amount of radiation exposure to the breasts, the high proportion of normal and near-normal ventilation perfusion scans in pregnant women with suspected PE, and the uncertainty caused by a finding of subsegmental PE on computed tomography (CT) pulmonary angiogram.
f. Chest CT pulmonary angiography: is the preferred first test in hemodynamically unstable pregnant patients, because this test is faster, can rule out other life-threatening diagnoses that mimic PE, and exposes the fetus to less radiation than ventilation-perfusion scintigraph. However, CT pulmonary angiography exposes the mother’s breasts to about 150 times more radiation than does ventilation-perfusion scintigraphy.
B. Amniotic fluid embolism.
1. A rare cause of respiratory failure in pregnancy with high morbidity and mortality.
2. Antemortem diagnosis based on clinical setting and exclusion of other causes of respiratory failure.
3. Finding fetal elements in maternal circulation in blood aspirated from right heart catheters lacks both sensitivity and specificity.
4. Dyspnea, tachypnea, tachycardia, and cyanosis during labor or early puerperium are classic. Shock or excessive bleeding may be the first sign. Symptoms may progress to cardiac arrest often within minutes. In those patients who survive the initial event, acute respiratory distress syndrome (ARDS) and disseminated intravascular coagulation (DIC) are common.
C. Venous air embolism.
1. Rare. Presentation is similar to amniotic fluid embolism.
2. Other potential findings: “mill wheel” murmur and ECG evidence of ischemia, right heart strain, and arrhythmias.
