The most likely diagnosis is ventilator-induced lung injury (VILI), which represents iatrogenic acute respiratory distress syndrome (ARDS) caused by mechanical ventilation. VILI is most likely to occur when tidal volume and/or plateau pressure are too high. It can occur even in patients with no evidence of lung injury at the time of intubation. This patient was ventilated throughout her surgery. Her ideal body weight is 48 kg (106 lb); based on this, the protective tidal volume would be 288 mL (6 mL/kg of ideal body weight). In addition to low tidal volume, protective ventilation also entails keeping the plateau pressure below 30 cm H₂O if possible. An early clue to nonprotective ventilator settings could have been an elevated plateau pressure, as in this patient when she arrived in the ICU.

Obesity hypoventilation syndrome could be seen in a patient with this body habitus and could include low respiratory system compliance, but this condition would not explain the airspace opacification on imaging, poor oxygenation, or worsening compliance over time.

Pulmonary embolism is always a risk postoperatively, especially in those who undergo orthopedic procedures, such as this patient. Pulmonary embolism would certainly worsen ventilation-perfusion matching and oxygenation, but it would not typically worsen lung compliance over the first 24 hours postoperatively.

ARDS can develop in response to transfusion of blood products when antibodies in transfused plasma activate recipient neutrophils; this is known as transfusion-associated lung injury (TRALI). This can occur after transfusion of any blood product, and it appears to be most likely when the volume of transfused plasma is high and comes from a multiparous female donor. TRALI is generally the least severe form of ARDS; however, it can be fatal if not managed appropriately. This patient received an autologous transfusion only and is not at risk for TRALI.