A 30-year-old woman is evaluated in labor and delivery for acute-onset dyspnea. An hour ago, the patient underwent an emergency cesarean delivery requiring intubation and general anesthesia for a category III fetal heart rate tracing due to placental abruption. The procedure was complicated by postpartum hemorrhage, and intraoperative transfusion of 2 units of packed red blood cells was required. The patient was extubated 15 minutes ago and now has significant shortness of breath and hypoxemia. Temperature is 38.3 C (101 F), blood pressure is 122/70 mm Hg, pulse is 114/min, and respirations are 24/min. Oxygen saturation is 84% on room air. Cardiac examination reveals no rubs or murmurs. Jugular venous pressure is normal. Pulmonary examination reveals bilateral crackles. The remainder of the examination is within normal limits. Chest x-ray shows infiltrates in the superior segments of the bilateral lower lobes. Which of the following is the most likely diagnosis in this patient?

Question

A 30-year-old woman is evaluated in labor and delivery for acute-onset dyspnea.  An hour ago, the patient underwent an emergency cesarean delivery requiring intubation and general anesthesia for a category III fetal heart rate tracing due to placental abruption.  The procedure was complicated by postpartum hemorrhage, and intraoperative transfusion of 2 units of packed red blood cells was required.  The patient was extubated 15 minutes ago and now has significant shortness of breath and hypoxemia.  Temperature is 38.3 C (101 F), blood pressure is 122/70 mm Hg, pulse is 114/min, and respirations are 24/min.  Oxygen saturation is 84% on room air.  Cardiac examination reveals no rubs or murmurs.  Jugular venous pressure is normal.  Pulmonary examination reveals bilateral crackles.  The remainder of the examination is within normal limits.  Chest x-ray shows infiltrates in the superior segments of the bilateral lower lobes.  Which of the following is the most likely diagnosis in this patient?

Quizplus · Accepted Answer

11ec25c8_da1e_0564_bc81_3d8dbb02b3eb_MD0003_00 This postpartum patient with acute-onset dyspnea and hypoxemia most likely has chemical pneumonitis from aspiration of acidic gastric contents. Pregnancy increases the risk for aspiration due to elevated progesterone, which delays gastric emptying and decreases esophageal sphincter tone. In addition, the gravid uterus increases intraabdominal pressure and promotes reflux. These obstetric factors, in combination with surgical risk factors (eg, sedation, recumbent positioning, emergency intubation), likely led this patient to aspirate. Aspiration leads to chemical pneumonitis through direct pulmonary injury from gastric acid. There is an ensuing inflammatory response, which causes localized pulmonary edema and alveolar collapse (ie, atelectasis). Chemical pneumonitis manifests clinically with low-grade fever, hypoxemia, and diffuse crackles on lung examination within hours of the aspiration event. Chest x-ray typically shows alveolar infiltrates in the dependent lung segments, which, in the recumbent position (ie, during cesarean delivery), are the superior segments of the lower lobes. The inflammatory process is usually self-limited and resolves with supportive treatment (eg, supplemental oxygen, ventilatory support). Unlike aspiration pneumonia (which often has an insidious presentation with cough), chemical pneumonitis does not typically require antibiotic therapy. A minority of patients may develop acute respiratory distress syndrome and have a more severe course. (Choice A) An acute hemolytic transfusion reaction due to ABO incompatibility can cause fever. However, the typical onset is within minutes of transfusion, and patients usually have hypotension and signs of hemolysis (eg, hemoglobinuria, acute renal failure, disseminated intravascular coagulation [DIC]). (Choice C) Left ventricular failure (eg, due to peripartum cardiomyopathy) can lead to cardiogenic shock with dyspnea due to acute pulmonary edema; however, increased jugular venous pressure and diffuse (not localized) infiltrates are expected. (Choice D) The risk of pulmonary embolism (PE) is increased in the peripartum period. Hypoxemia and respiratory distress can occur with acute PE; however, jugular venous distension and clear lungs are also expected. Educational objective: Chemical pneumonitis is typically a self-limited inflammatory response caused by direct pulmonary injury from aspirated acidic gastric contents. Patients typically develop dyspnea, hypoxemia, and alveolar infiltrates in the dependent lung segments within hours of aspiration. References: Interventions at caesarean section for reducing the risk of aspiration pneumonitis. (http://www.ncbi.nlm.nih.gov/pubmed/24497372) Ultrasound evaluation of the stomach and gastric emptying in pregnant women at term: a case-control study. (http://www.ncbi.nlm.nih.gov/pubmed/26554613)

A 30-Year-Old Woman Is Evaluated in Labor and Delivery for Acute-Onset