Page 1798 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

CHAPTER 127: Critical Illness in Pregnancy 1267

sex, criminal abortions using air, and insufflation of the vagina during blockade may assist in cardiopulmonary stabilization by decreasing
gynecologic procedures. Air is thought to enter subplacental venous oxygen consumption and avoiding the intrathoracic pressure effects of
140
sinuses, embolize through the venous circulation, and obstruct pul- active ventilatory effort. Inhaled nitric oxide has not been well studied
monary blood flow. Signs and symptoms include a continuous cough, in pregnant patients. Prone positioning also has not been studied,
dyspnea, lightheadedness, diaphoresis, tachypnea, cyanosis, tachycardia, although the gravid state makes this maneuver difficult. 128,153 Delivery
and hypotension. A mill wheel murmur or bubbling sound is occasion- for severe ARDS cannot be universally recommended; decisions are
ally heard over the precordium. With a significantly sized embolism, made for individual cases, weighing the theoretical improvements in
hypotension is often followed by respiratory arrest. Arrhythmias and ventilation against the physiologic costs of delivery. 152
evidence of right heart strain and ischemia have been noted on ECG.
If readily available, evaluation of the right and left sternal borders by ■ CONSIDERATIONS OF MECHANICAL VENTILATION IN PREGNANCY
Doppler ultrasound is the most sensitive noninvasive diagnostic test. The indications for intubation and mechanical ventilation are not sig-
151
Patients who survive an initial cardiopulmonary collapse may develop of
noncardiogenic pulmonary edema. nificantly changed by pregnancy, although the adjusted normal Pa CO 2
27 to 34 mm Hg of pregnancy should be considered when interpreting
1
Management: When venous air embolism is suspected, the patient blood gases and the need for intubation. In the setting of progressive
should immediately be placed in the left lateral decubitus position respiratory distress, a decision regarding intubation is best made in col-
to direct the embolus away from the right ventricular outflow tract. laboration with the critical care physician, obstetrician, and neonatolo-
Trendelenburg positioning has also been advocated, although it has gist. NIPPV for acute respiratory failure has not been well studied in
not been demonstrated to improve outcomes. To facilitate resorption pregnancy. In the stable patient able to protect their airway, NIPPV may
of nitrogen, 100% oxygen should be provided. If available, and if the be reasonable for certain conditions, such as mild hypoxemia associated
clinical status permits, hyperbaric oxygen will also aid in resorption. with readily reversible pulmonary edema. Theoretical limitations to
Aspiration of air from the right atrium is not often successful, but can NIPPV include pregnancy-related upper airway edema and an increased
be attempted as a salvage intervention. Acute right heart failure con- risk of aspiration, although a definitive aspiration risk associated with
157
tributes to clinical deterioration, and inotropic support with dobuta- NIPPV use in pregnancy has not been established. If respiratory
mine may be helpful. If cardiac arrest occurs, chest compressions may failure is imminent, intubation and mechanical ventilation should be
therapeutically disperse larger emboli. performed electively. The institution of mechanical ventilation early in
■ ARDS and fetus, and permits identification and treatment of reversible fac-
the course of respiratory failure facilitates stabilization of the mother
ARDS is defined by the acute onset of diffuse, noncardiogenic pulmo- tors in a controlled setting. When delivery is indicated in the setting of
respiratory failure, mechanical ventilation can support successful surgi-
<200. The pathophys-
nary edema which results in a ratio of Pa O 2 to Fi O 2 cal delivery. If maternal death occurs, fetal viability can be maintained
iology and management of ARDS is reviewed extensively elsewhere (see throughout pregnancy with mechanical ventilation.
Chap. 52). However, several considerations for ARDS during pregnancy Tracheal intubation can be a high-risk procedure in pregnant patients.
are emphasized here. ARDS in pregnancy is associated with maternal Intubation failure occurs more frequently than in nonpregnant patients,
and fetal mortality, perinatal asphyxia, and premature delivery. As with and is associated with morbidity and mortality. Several difficulties in
158
nonpregnant patients, sepsis is the most common cause of ARDS dur- airway management should be anticipated (Table 127-11), and control
ing pregnancy. While aspiration is historically an important cause, the of the airway should be achieved by a skilled practitioner. Pharyngeal,
152
incidence of has dramatically declined with the widespread adoption of laryngeal, and vocal cord edema are common, and the increased vas-
aspiration precautions in pregnant patients. Preeclampsia and amniotic cularity of the upper airway may lead to bleeding from even minor
fluid embolism are other pregnancy-related conditions associated with intubation-related trauma. 128,130 A relatively small endotracheal tube
the development of ARDS.
may be necessary, and nasotracheal intubation is best avoided because
Management: A meticulous evaluation for occult infection, includ- of nasal narrowing and hyperemia. Finally, due to the risk of aspiration
3
ing chorioamnionitis, is an important part of ARDS management. during pregnancy, mask ventilation should be avoided and the applica-
Tracheal intubation and mechanical ventilation should be instituted tion of cricoid pressure during intubation is strongly recommended. 159
in an expectant fashion for patients with unstable hemodynamics or Most patients require sedation during intubation and mechanical
progressive hypoxemia. Although some experts have recommended ventilation. Propofol is a pregnancy category B hypnotic agent (see
of pregnancy (27-34 mm Hg), the ben- Chap. 22), and has been used safely in pregnancy. Morphine and fen-
maintaining the lower Pa CO 2
efit of this has not been established. The salient guiding principles tanyl (pregnancy category C) are also generally safe during pregnancy.
of ARDS ventilator management include use of a low tidal volume If benzodiazepines (pregnancy category D) are used early in pregnancy,
strategy to avoid over distention of alveoli, and maintaining plateau the lowest dose and shortest possible duration are recommended, as
pressures less than 30 cm H O to minimize the risk of barotrauma. benzodiazepines carry a theoretical risk of cleft palate and other birth
153
2
While a low tidal volume strategy of 6 mL/kg (based on prepregnancy defects. All of these agents cross the placenta, and if given near the time
weight) has not been studied in pregnant patients, outcomes of this of delivery immediate intubation of the neonate may be required. Non-
strategy in nonpregnant patients are compelling and support its use depolarizing neuromuscular blocking agents including cisatracurium,
in most patients with ARDS. Pregnancy is not an absolute contrain-
dication to permissive hypercapnea. However, significant acidemia
154
impairs fetal carbon dioxide transfer and oxygen extraction, and TABLE 127-11 Considerations in Airway Management of Pregnant Patients
should be avoided. Conversely, alkalosis should be avoided, as ani- Risk Factors Response
155
mal studies suggest an associated decrease in uteroplacental flow. 3,156 , ↓ FRC Pre-oxygenate
2
The gravid uterus can impair chest wall mechanics, resulting in higher Low O reserve: ↑ V O 2
than normal airway pressures. Nonetheless, when diffuse lung injury Highly vascular airway Avoid nasal intubation
is present, it is the predominant contributor to increased plateau Airway edema Employ smaller diameter tracheal tube
pressures and high plateau pressures in this setting most often reflect Altered anatomy from weight gain Proper positioning
decreased parenchymal compliance. Sufficient PEEP should be pro-
153
(<0.6). To prevent fetal Increased aspiration risk Acid reduction therapies
vided to correct hypoxemia at a nontoxic Fi O 2
in pregnant patients is greater than 90 mm Hg, a Rapid sequence induction
distress, the goal Pa O 2
higher minimum value than in nonpregnant patients. Neuromuscular FRC, functional residual capacity; VO 2 , oxygen consumption.

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