Page 1797 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

1266 PART 11: Special Problems in Critical Care

with isoniazid, rifampin, and ethambutol plus pyridoxine until drug delivery. Less established risk factors include amniotomy, cesarean
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susceptibility testing is complete. All three agents cross the placenta, section, insertion of intrauterine fetal or pressure monitoring devices,
but have not been shown to be teratogenic. In contrast, streptomycin is and term pregnancy in the presence of an intrauterine device. It is
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known to be harmful for the fetus, and should not be used during preg- important to note that while most cases occur during labor and delivery,
nancy. PCP should be treated with trimethoprim- sulfamethoxazole. AFE may occur during first- and second-trimester abortions, or after
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The indications for corticosteroids in severe PCP infection are the trauma. There is also a case report of a spontaneous occurrence at 20
same as for nonpregnant patients. No teratogenic effects of acyclovir weeks of gestation. 149
have been noted in animal studies, and in pregnant patients with The classic and most common presentation of AFE is the abrupt
cutaneous varicella infection, acyclovir should be started at the first onset of respiratory failure, marked by severe dyspnea, tachypnea, and
sign of respiratory involvement. Amphotericin B is considered safe hypoxemia, during labor or soon after delivery. This is often followed
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during pregnancy, and its use has dramatically reduced mortality from by the development of cardiovascular collapse, hemorrhage, and sei-
disseminated coccidioidal infections. Fluconazole and likely other zures. While less common, shock or bleeding can also be the initial
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azole antifungals are teratogenic; their prolonged use is best avoided. 144 presentation of AFE. The mechanisms of respiratory and circulatory
■ ASPIRATION failure remain controversial. While amniotic fluid and particulate matter
may enter the maternal circulation, pulmonary vascular obstruction is
12
Aspiration is a well-described and potentially serious complication of thought to be a minor factor in the immunopathogenesis. A role for an
pregnancy. Due to improved prevention strategies, the related mor- anaphylactoid reaction to circulating fetal material has been suggested,
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bidity and mortality have dramatically decreased since Mendelson’s but remains unproven. 128,148 In animal models of AFE, acute elevations in
initial description of aspiration in pregnancy. The severity of aspiration the pulmonary artery pressure and CVP with subsequent hypotension,
injury is related to the volume, pH, and bacterial burden of aspirated indicative of right heart failure, have been observed and attributed to
material, the presence of particulate material, and the host resistance vasoconstricting arachidonic acid metabolites present in the amniotic
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to possible subsequent infection. The initial injury is a chemical pneu- fluid. In humans, the acute increase in pulmonary vascular resistance
monitis that occurs 24 to 72 hours after the aspiration event; diffuse that is noted in many cases supports acute right heart failure as an
lung injury, including ARDS, may develop as a complication. When it important and primary event in the pathogenesis. Pulmonary edema
occurs, bacterial pneumonia is a late complication and tends to be focal is also often present and, when out of proportion to Ppw, is attributed
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and polymicrobial. to capillary leak. In some patients the pulmonary vascular resistance
is only minimally increased, and significant left ventricular dysfunc-
Management: Prevention of aspiration should be the primary goal of tion with an elevated Ppw are present, suggesting that left ventricular
all physicians assessing and managing a pregnant patient’s airway. All dysfunction may also contribute to pulmonary edema and circulatory
pregnant patients, regardless of the time of their last meal, should be collapse; this may be most evident later in the course of AFE. 148,150
considered to have a full stomach. The application of cricoid pressure A proposed two-phase model of disease, marked by prominent
during intubation is crucial. Once aspiration has occurred, treatment right heart failure early followed by the subsequent development of
is supportive (see Chap. 59). Antibiotics should be given if bacterial left heart dysfunction, accounts for the variety of cardiovascular find-
pneumonia is suspected. ings reported for AFE. Nearly all patients who survive the initial few
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■ TOCOLYTIC THERAPY hours will develop laboratory evidence of DIC, and DIC-related bleed-
ing complications are generally substantial. The combination of severe
The use of β-adrenergic agents to inhibit preterm labor leads to pulmo- cardiac, pulmonary, and coagulopathic insults underlies the substantial
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nary edema in up to 4% of patients receiving these drugs. The inci- mortality associated with AFE.
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dence of pulmonary edema from tocolysis is increased in women with Management: Treatment is supportive and is aimed at ensuring
multiple gestations, concurrent infection, or those receiving corticoste- adequate oxygenation, stabilizing the circulation, and controlling
roid therapy. Pulmonary edema typically develops during or within bleeding. The initial management includes intubation and mechanical
1
24 hours after discontinuation of tocolytic therapy. The pathogenesis ventilation with lung protective low tidal volumes and a respiratory
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is unknown, although note of a normal left ventricular function and rate that avoids significant respiratory acidosis. PEEP is titrated,
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Ppw in most cases has led to speculation that tocolytics mediate low- >90 mm Hg and a fraction of inspired
pressure capillary leak. As pulmonary edema has not been associated as tolerated, to achieve a Pa O 2
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) ≤0.6. Sedation and paralytics allow complete rest of
with similarly high doses of β-adrenergic agonists used to treat asthma, oxygen (Fi O 2
the respiratory muscles and may facilitate hemodynamic stability in
increased circulatory volume may also play a role in tocolysis-induced those with refractory hemodynamic compromise. An echocardio-
pulmonary edema. Indeed, a positive fluid balance is often noted in the gram should be obtained urgently to determine the degree of left
hours to days preceding the onset of overt pulmonary symptoms after and right heart failure, as optimal management of each are critical
tocolytics. Tachypnea, tachycardia, and signs of pulmonary edema are determinants of outcome. Fluid resuscitation is guided by status of
observed on examination, and blood gas analysis reveals hypoxemia the circulating volume and right heart function. Systemic vasodilation
and hypocapnea. With appropriate supportive care, the clinical course may be prominent, and vasoactive drugs are frequently necessary for
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typically is marked by a quick and complete return to baseline function. blood pressure support. Rare case reports attest to the successful
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Management: Treatment is supportive, and consists of discontinuation use of inhaled nitric oxide, extracorporeal membrane oxygenation
of tocolytic therapy, the provision of supplemental oxygen, and diure- (ECMO), and intra-aortic balloon pump therapies in refractory
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sis. Occasionally, positive pressure ventilation may be required. The cases. DIC should be anticipated, and if possible a hematologist
response to diuretics in tocolysis pulmonary edema is usually prompt. should be consulted early. Recombinant factor VIIa has been used for
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Due to increased glomerular filtration, the dosing of diuretics is usually refractory bleeding in AFE. In undelivered patients, delivery should
lower than in nonpregnant patients. be performed expeditiously.
■ AMNIOTIC FLUID EMBOLISM ■ VENOUS AIR EMBOLISM
Amniotic fluid embolism (AFE) is a rare but significant cause of mater- Although the incidence of venous air embolism in pregnancy is low,
nal mortality. The course is fulminant and often fatal. For survivors, the associated risk is high and venous air embolism accounts for up to
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there is a high incidence of central nervous system dysfunction. Risk 1% of all maternal deaths. While it can occur during normal labor,
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factors for AFE include advanced age, multiparity, and device assisted risk factors are often identified and include placenta previa, orogenital

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