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Chapter 11: Acute Respiratory Distress Syndrome

A 32-year-old man who was recently diagnosed with acute lymphoblastic leukemia and is currently undergoing induction chemotherapy is sent to the emergency department (ED) by his oncologist for fevers and shortness of breath of 4 days’ duration. In the ED, he is found to be in moderate respiratory distress, hypotensive, and febrile to 39.4°C. His labs reveal leukopenia and neutropenia. His chest x-ray shows diffuse bilateral alveolar infiltrates. He is diagnosed with pneumonia complicated by ARDS, given intravenous fluids, intubated for severe hypoxemia, and started on volume-controlled ventilation in the ED with the following settings: respiratory rate (RR) of 25 breaths/min, TV of 420 mL (which translates to 6 mL/kg for his calculated PBW of 70 kg), PEEP of 5 cm H2O and an FiO2 of 1.0. A postintubation arterial blood gas (ABG) on these settings shows a pH of 7.30, a partial pressure of carbon dioxide (PCO2) of 48 mmHg, and an arterial pressure of oxygen (PaO2) of 46 mmHg. The peak airway pressure on the current ventilator settings is 25 cm H2O, and the plateau pressure is measured as 23 cm H2O. Which of the following ventilator interventions is the most appropriate next step to improve this patient’s hypoxemia?

A. Convert to HFOV

B. Increase the RR to 30 breaths/min

C. Increase the PEEP to 10 cm H2O

D. Increase the TV to 450 mL

C. Increase the PEEP to 10 cm H2O

The next immediate priority in management is to address the inadequate oxygenation in this patient with severe ARDS who is already receiving FiO2 of 1.0. In addition to ensuring adequate oxygenation, ARDS mechanical ventilation principles are designed to limit VILI. The objective is to apply PEEP at a level that helps achieve adequate oxygenation through maintenance of alveolar recruitment while also rendering the baby lung less susceptible to VILI. PEEP is being underutilized in this patient with severe ARDS, so an increase is warranted and could be preceded by a recruitment maneuver. “Optimal” PEEP for a given patient would be that level that maximizes recruitment (or minimizes tidal derecruitment), while avoiding overdistention and its complications. The best method of determining optimal PEEP remains controversial. Although increasing the respiratory rate (choice B) or tidal volume (choice D) could improve oxygenation, both maneuvers could also compromise lung-protective ventilation and promote barotrauma. Conversion to HFOV (choice A) may or may not produce an oxygenation benefit but cannot be advocated prior to exhaustion of conventional ventilatory strategies due to evidence for worsened survival with HFOV.

Which ...

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