ARDS In Class Case

CASE Information: LOUIS CHEN
Louis Chen (he/him) is a 25-year-old male admitted through the emergency department when he developed a cough, temp of 104 F and headache. The patient was diagnosed with pneumonia, but he rapidly deteriorated with a respiratory rate of 40/min and acute dyspnea. His ABG showed a PaO2 of 48
mm Hg on 60% of FiO2 delivered via green venturi high flow system. He was diagnosed with ARDS after a chest x-ray was taken. Louis was sedated to a RASS -4, intubated, and mechanically ventilated. He was on Assist Control mode with RR 12, VT 350, PEEP 10.5 cm H2O and FiO2 100 %. An in-line suction catheter was present. Louis was a software engineer. He was very active and coached soccer on the weekends. Louis lives in New York in a 10th floor apartment with his girlfriend.


What is ARDS? Review the stages of ARDS. What stage is Louis in?

  • ARDS stands for Acute Respiratory Distress Syndrome, a severe lung condition that occurs when fluid builds up in the air sacs, preventing proper oxygenation of the blood.


  • The stages of ARDS are classified based on the severity of the hypoxemia:

    • Mild ARDS: PaO2/FiO2 ratio > 200 mmHg and ≤ 300 mmHg

    • Moderate ARDS: PaO2/FiO2 ratio > 100 mmHg and ≤ 200 mmHg

    • Severe ARDS: PaO2/FiO2 ratio ≤ 100 mmHg

  • To determine the stage Louis is in, we need to assess his PaO2/FiO2 ratio and clinical presentation.

  • He is in the exudative phase, which is characterized by increased permeability of the alveolar-capillary membrane, leading to pulmonary edema, atelectasis, and impaired gas exchange.

How did Louis Chen’s pneumonia develop into ARDS?

  • This progression can occur due to a combination of factors, including the severity of the initial lung infection, the inflammatory response triggered by pneumonia, and any pre-existing comorbidities that may compromise respiratory function.

  • alveolar infection

  • alveolar wall injury

  • porous

Is Louis in respiratory failure? Why/why not, if so what type of respiratory failure?

  • Yes, Louis is in respiratory failure due to his significantly reduced oxygenation levels, as indicated by his low PaO2/FiO2 ratio. This situation qualifies as type 1 respiratory failure, characterized by hypoxemia without hypercapnia, which is often seen in conditions like ARDS.

  • He is hypoxemic because his PaO2 is below 60mmHg along with alveolar flooding, leading to insufficient oxygen delivery to the tissues, which can result in further complications if not promptly addressed.

Discuss the details of the patient’s mechanical ventilation. What type of mode is the patient on - can Louis increase his tidal volume - why or why not? Why is the patient sedated?

  • Louis is currently on assist-control ventilation (ACV) mode, which allows him to maintain a minimum number of breaths while also permitting him to initiate additional breaths if needed. However, his ability to increase tidal volume is limited due to the underlying lung pathology associated with ARDS, which results in decreased lung compliance and restricted lung volumes. Therefore, while he can initiate breaths, the tidal volume he can achieve may not be sufficient to meet his oxygenation needs.


    He is sedated to ensure comfort during mechanical ventilation and to minimize respiratory drive, allowing the ventilator to control his breathing effectively. Sedation also helps prevent anxiety and agitation, which can further compromise his respiratory status.

Explain the reason for his current PEEP settings and implications. How can it help? What are potential side effects?

  • The current PEEP (Positive End-Expiratory Pressure) settings are utilized to maintain alveolar recruitment and prevent atelectasis, which is crucial in patients with ARDS. By keeping the alveoli open at the end of expiration, PEEP enhances functional residual capacity and improves oxygenation by increasing the surface area available for gas exchange. Since the PEEP is above 10, he is in critical severe hypoxemia.


    This strategy can help improve ventilation-perfusion matching and reduce shunting, thereby optimizing the patient's oxygenation levels. However, potential side effects of elevated PEEP include decreased cardiac output due to increased intrathoracic pressure, barotrauma, and impaired hemodynamics, which may necessitate careful monitoring and adjustments to ensure overall stability.

Why is Louis on 100% FiO2? What are the implications?

  • Louis is on 100% FiO2 to maximize oxygen delivery and combat severe hypoxemia resulting from ARDS. In this critical condition, the lungs are unable to effectively oxygenate blood due to impaired gas exchange, thus requiring high levels of supplemental oxygen to maintain adequate oxygen saturation.

  • The implications include oxygen toxicity, V/Q mismatch, and the potential for further lung injury, necessitating careful titration of FiO2 to balance oxygen needs with the risk of adverse effects.

What is the purpose of the “in line suction catheter”

  • The purpose of the "in line suction catheter" is to facilitate the removal of secretions from the airway without the need to disconnect the patient from the ventilator, thereby reducing the risk of ventilator-associated pneumonia and maintaining optimal lung function during mechanical ventilation.