Mechanical Ventilation and Delivery During Pregnancy

FOR RELATED ARTICLE, SEE PAGE 554

Before the COVID-19 pandemic, respiratory failure that required mechanical ventilator support in pregnancy was a relatively uncommon event, occurring at a rate of approximately 1 in 10,000 pregnancies.¹ Although significant literature has been published over the past 20 years to guide optimal, safe mechanical ventilation in ARDS, all of these studies specifically excluded or did not report on pregnant patients. The exclusion of pregnant patients from research studies is a well-recognized and concerning phenomenon²; however, in the case of mechanical ventilation, the issue was largely the dearth of cases. Unanswered questions in this field include the effects of pregnancy on respiratory system physiologic condition, optimal blood gas targets, and the role of delivery in improving maternal and fetal outcome. Several small retrospective case series previously have attempted to address these issues.^{3 , 4}

The COVID-19 pandemic was associated with increased severity of illness among pregnant patients, with a higher need for ICU care and ventilator support than age-matched nonpregnant women.⁵ Although not an easy time for ICU research, the pandemic was an opportunity to gain more knowledge about this specific population. Some retrospective case series have been published since then that have somewhat advanced our knowledge.^{6 , 7} In this issue of CHEST, Vasquez et al⁸ provide binational prospective data on the mechanical ventilation of pregnant patients. These authors are to be congratulated on having the foresight and determination to collect these valuable data during this difficult time.

The group studied 91 pregnant and postpartum patients with COVID-19 who had been admitted to 21 ICUs in Argentina and Colombia during the second wave of the pandemic. Of these, 69 patients required invasive mechanical ventilation, and 47 patients delivered while on the ventilator. High-flow nasal oxygen was used effectively as the only respiratory support in 22% of patients, with excellent maternal and neonatal outcome. Because of the prospective nature of their data collection, they were able to track mechanical ventilation parameters that are notoriously difficult to generate retrospectively, which include plateau pressure, driving pressure, and static compliance. Respiratory mechanics were similar to the general COVID-19 population.⁹ Plateau pressures were maintained at < 30 cm H₂O in survivors, with an increase above this level in nonsurvivors. Similarly, driving pressure was on average < 14 cm H₂O in survivors and significantly higher in nonsurvivors. The investigators prospectively tracked respiratory parameters before and after delivery, which was completed predominantly by cesarean delivery for maternal reasons. Although PaO₂/Fio ₂ ratio increased after delivery (from a mean of 134 to 192 mm Hg over 24 h), there was no change in static compliance or driving pressure. Outcome was acceptable in this critically ill cohort, with a maternal mortality rate of 17.5 % and perinatal mortality rate of 15.4%. In patients whose condition required ventilation, the mortality rate was lower than in the general COVID-19 population, perhaps explained by younger age and fewer comorbidities.¹⁰

Delivery of the pregnant patient with ARDS is often proposed in an attempt to improve the maternal respiratory condition and remove the complicating factor of a fetus. However, data to support a maternal benefit are limited. Studies on the impact of delivery on lung function previously were restricted to retrospective case series and have included respiratory failure from many causes. A retrospective case series of 10 patients who delivered while on mechanical ventilation demonstrated a modest benefit, but only in a proportion of patients.⁴ A larger case series evaluated the respiratory effects of delivery in 71 patients, which again showed significant variation in the benefits.³ Little oxygenation or compliance benefit was noted in women with nonobstetric causes for respiratory failure (eg, pneumonia, sepsis, pancreatitis) although a small benefit was noted in those patients with obstetric conditions (eg, preeclampsia, hemorrhage). A European retrospective cohort analyzed 27 women with COVID-19 who were delivered while on mechanical ventilation.⁷ Oxygenation and driving pressure, a parameter associated with lung injury, demonstrated improvements after delivery predominantly in obese patients, although the condition of a few women deteriorated after delivery. The study from Vasquez et al⁸ provides additional high-quality prospective data to this knowledge base. Overall, these data demonstrate the lack of universal significant improvement in compliance and driving pressure with delivery. Delivery is associated with a small improvement in oxygenation, which cannot be used as a surrogate for improved outcomes.¹¹

Cesarean section is often the mode of delivery, and its potential risks during ARDS have not been explored adequately in the literature. Delivery can be associated with bleeding or worsening right ventricular dysfunction in the context of severe ARDS, because of the increase in central circulation that is associated with involution of the uterus. Neonatal risks are also significant with iatrogenic delivery, which led to early prematurity in 36% of the neonates in this study by Vasquez et al.⁸

Although there is a natural tendency for intensive care physicians to seek to remove the complicating factor of a gestation in critically ill pregnant patients, this cannot be justified by the assumption that delivery will improve maternal well-being. Any surgical procedure carries risks, particularly in the unstable patient with severe ARDS. Our suggestion is to deliver only for usual obstetric indications, which may include fetal distress caused by maternal hypoxemia. Finally, we think it is important to reiterate a big picture mantra overarching the treatment of the ill pregnant patient: “Treat a pregnant woman as you would a nonpregnant woman, unless there is a clear reason not to.”¹²