Acute Respiratory Failure in Pregnancy: ICU Management and Anesthetic Considerations

Ventilation Management

Noninvasive Ventilation (NIV)

• High-flow nasal cannula (HFNC) involves administering 100% humidified and heated oxygen at a flow rate of up to 60 L/min. HFNC may reduce the risk of invasive mechanical ventilation in patients with hypoxemic respiratory failure and is considered safe and reasonable to trial in pregnant patients.¹
• The use of NIV with bilevel positive airway pressure and continuous positive airway pressure is controversial in ARDS, as it has not been shown to reduce the incidence of intubation and mechanical ventilation. Furthermore, the physiologic changes of pregnancy that predispose parturients to aspiration make NIV a less attractive option.
• Failure to clinically improve with HFNC or NIV should be identified promptly, and intubation with mechanical ventilation should be pursued.

Intubation and Mechanical Ventilation

• Hormonal changes in pregnancy lead to increased tissue friability and airway edema, predisposing to difficult intubation.
• Physiological changes in pregnancy include increased tidal volume, decreased functional residual capacity, decreased total respiratory compliance, increased minute ventilation, and increased oxygen consumption, which predisposes these patients to rapid desaturation in the setting of apnea.²
• Pregnant patients with ARDS should be managed on the ventilator with settings consistent with ARDS Network ventilation with low tidal volumes of 6-8 mL/kg predicted body weight and goal plateau pressures of ≤ 30 cm of water.³
• The physiologic changes in pregnancy result in a higher PaO₂ (90-100 mmHg) and lower PaCO₂ (28-32 mmHg). A goal PaO₂ ≥ 70 mmHg and saturation ≥ 95% is recommended to avoid fetal distress secondary to hypoxia. A goal of PaCO₂ ≤ 40 mmHg is generally recommended to avoid fetal hypercarbia.
• Sedation and analgesia should be administered to pregnant women who are intubated and mechanically ventilated for comfort and ventilatory synchrony. Propofol, opioids, benzodiazepines, and dexmedetomidine may all be appropriate.

Refractory Hypoxemia

Neuromuscular Blockade

• Early initiation of neuromuscular blockade for refractory ARDS may decrease mortality.
• There are no contraindications to neuromuscular blockade during pregnancy as a rescue therapy for refractory ARDS, and the use of this strategy has been extensively described in pregnant patients.⁴

Prone Positioning

• Prone positioning in mechanically ventilated patients with severe ARDS decreases mortality, with benefits most pronounced with longer durations (>12 hours/day).⁵
• Prone positioning is feasible in pregnant patients but requires attention to positioning and padding to prevent aortocaval compression, offload the uterus, and allow access to fetal monitoring.

Pulmonary Vasodilators

• Pulmonary vasodilators are well tolerated and may be beneficial in pregnant patients with severe ARDS.
• Inhaled vasodilators including nitric oxide (iNO) and inhaled prostaglandins have been shown to improve the PaO₂ in patients with severe ARDS; however, this benefit has not translated to improvement in mortality or days on mechanical ventilation.⁷
• Inhaled epoprostenol has been shown to have comparable clinical efficacy to iNO for improvement in oxygenation and ventilation in patients with severe ARDS and no difference in clinical outcomes including length of stay, duration of mechanical ventilation, and mortality at a lower cost.^8,9

Extracorporeal Membrane Oxygenation (ECMO)

• In cases of severe, refractory ARDS, venovenous ECMO may be utilized as a rescue therapy.
• The most recent systematic reviews examining the use of ECMO in pregnancy for ARDS show superior survival rates (nearly 80%) compared to the general population for respiratory indications (58%).^10-12
• Neonatal complications are higher in pregnancies where the mother undergoes ECMO during pregnancy, including preterm delivery, intensive care unit admission, and mortality. Delivery of the fetus prior to initiation of ECMO is not a requirement and is only initiated if needed for maternal and/or fetal indications.

Delivery Considerations

Fetal Monitoring

• Maternal condition is often reflected in the fetal status, and fetal heart rate monitoring is routinely performed in critically ill obstetrical patients.
• Intermittent (daily or multiple times during the day) or continuous fetal heart monitoring may be utilized, depending on the patient’s acuity, with an individualized approach based on multidisciplinary input.
• There is no expert consensus for guiding the frequency of checks, and the decision should be made case-by-case based on input from interdisciplinary teams, neonatal resuscitative resources, and patient preferences.

Timing of Delivery

• Equipment for emergency delivery and neonatal resuscitation should be available at the bedside of any pregnant patient in the intensive care unit.
• The decision to proceed with delivery of the fetus is complex and case-specific; multidisciplinary teams including maternal fetal medicine, critical care, obstetric anesthesiology, and neonatology should weigh the relative risk-benefit for each case with consideration of gestational age, underlying illness, and maternal status.
• Prolonging the pregnancy to allow fetal growth in utero (ideally beyond 32 weeks gestation) is generally the goal.

Method of Delivery

• Most women with severe ARDS are delivered via cesarean section.
• Fluid intake should be restricted as much as possible while maintaining adequate oxygenation and blood pressure.
• An individualized plan for delivery should be made based on the gestational age, patient status, etiology of respiratory failure, need for advanced therapies, and clinical stability.

Anesthetic Considerations

• Neuraxial analgesia and anesthesia are associated with decreased morbidity in pregnant patients and reduced fetal exposure to systemic medications, as well as superior pain control and reduced oxygen consumption.
• The decision to proceed with neuraxial analgesia or anesthesia in patients with acute lung disease is individual and should take into consideration additional conditions and therapy, fluid status, and presence of infection.
• In obstetrical patients who are already intubated and mechanically ventilated, there is no data as to the added benefit of a neuraxial procedure for cesarean delivery, and they are more likely to receive general anesthesia.
• Women who are on anticoagulation for any reason, including mechanical circulatory support, require a plan for cessation timing and monitoring if neuraxial anesthesia is pursued, given the risk of epidural hematoma.