In cases of severe acute lung injury, providing adequate oxygenation of peripheral tissues is balanced against maneuvers that further aggravate lung injury. At least intuitively, increasing oxygen delivery should produce a corresponding increase in tissue uptake, but this is diicult to measure. Support of systemic perfusion with intravenous crystalloid and blood is imperative. As discussed earlier, the trial conducted by the National Heart, Lung, and Blood Institute (2006) showed that pulmonary artery catheter use did not improve outcomes. Because sepsis is commonplace in lung injury, vigorous antimicrobial therapy is given for infection, and any necrotic tissues are debrided. Oxygen delivery can be greatly improved by correction of anemia. Speciically, each gram of hemoglobin carries 1.25 mL of oxygen when 90-percent saturated. By comparison, increasing the arterial P02 from 100 to 200 mm Hg results in the transport of only 0.1 mL of additional oxygen for each 100 mL of blood.
Reasonable goals in caring for the woman with severe lung injury are to attain a Pao2 of 60 mm Hg or 90-percent oxygen saturation using an inspired oxygen content < 50 percent and positive end-expiratory pressures < 15 mm Hg. With regard to the pregnancy, it remains controversial whether delivery of the fetus improves maternal oxygenation (Mallampalli, 2010). In a study of 29 women undergoing mechanical ventilation, 10 were delivered while intubated (Lapinsky, 2015). This was associated with a modest improvement in respiratory function in perhaps half, but no factors were identiied that predicted a better outcome.
Noninvasive ventilation, that is, positive pressure ventilation by face mask, may be efective in some women in early stages of pulmonary insuiciency (Duarte, 2014). Early intubation is preferred in the gravida if respiratory failure is more likely than not, and especially if it appears imminent. Many successful formulas for mechanical ventilation are employed, and initially a tidal volume :;6 mLlkg is optimal (Levy, 2015; Schwaiberger, 2016). High-frequency oscillation ventilation (HFOV) is controversial in ARDS (Ferguson, 2013; Slutsy, 2013). Adjustments are made to obtain a Paoz>60 mm Hg or a hemoglobin oxygen saturation 290 percent and a Pacoz of 35 to 45 mm Hg. Lower levels for Paoz are avoided, because placental perfusion may be impaired (Levinson, 1974).
For women who require ventilation for any length of time, the maternal mortality rate is 10 to 20 percent. In a study of 51 such women, almost half had severe preeclampsia, and most required intubation postpartum. Eleven were delivered while being ventilated, and another six were discharged undelivered (Jenkins, 2003). here were two maternal deaths, including a woman who died as a complication of tocolytic treatment. In three other reports, maternal mortality rates ranged from 10 to 25 percent (Chen, 2003; Lapinsky, 2015; Schneider, 2003). In most cases, delivery did not improve maternal outcome.