Acute Respiratory Distress Syndrome Physiology

ARDS is a 

V/Q mismatch issue

Compliance

P/F ratio

Shunt

Intervention	2017 ATS/ESICM/SCCM	2024 ATS	2023 ESICM
Low tidal volume	Strong in favor	Retained	Strong in favor
Prone positioning	Strong for severe ARDS	Retained	Strong for moderate–severe ARDS
V–V ECMO	No recommendation for or against	Conditional for severe ARDS	Strong for severe ARDS
Corticosteroids	Not addressed	Conditional in favor	Not addressed
Neuromuscular blockade	Not addressed	Conditional for early, severe ARDS	Strong against for routine use in moderate-severe ARDS
Higher PEEP	Conditional for moderate–severe ARDS	Conditional for moderate–severe ARDS	No recommendation for or against use of high PEEP/FiO2 table in ARDS
Recruitment maneuvers	Conditional in favor	Strong recommendation against prolonged RM	Strong recommendation against prolonged RM
Oscillatory ventilation	Strong recommendation against	Retained	Not addressed

Vtt

Prone positioning

Strong in favor

PEEP - conditional / No

Corticosteroids

NMBA

Recruitment maneuvers (Oscillatory ventilation)

Tis resulted in four conditional recommendations for corticosteroids, VV-ECMO, NMBA, and higher PEEP, and one strong recommendation against prolonged recruitment maneuvers, in addition to retaining strong recommendations from 2017

What is the likely diagnosis in a patient with respiratory distress, crackles on examination, hypoxemia, and diffuse, bilateral alveolar infiltrates not due to CHF/fluid overload?

Complications of drowning are a result of hypoxemia from fluid aspiration. The aspirated liquid washes out alveolar surfactant, causing pulmonary edema, respiratory insufficiency, and acute respiratory distress syndrome

ARDS can develop insidiously over the next 72 hours

Patients should be admitted to the hospital and monitored closely for dyspnea, cough, cyanosis, and crackles.

 

V/Q Mismatch

Pulmonary Physiology

Intrapleural pressures

Acute Respiratory Distress Syndrome (ARDS)

destruction of surfactant via phospholipase A2

damage to capillary endothelium and alveolar epithelium

protein escapes from vascular space

fluid pours into interstitium

Most patients with ARDS require mechanical ventilation with the following goals:

Avoiding complications of mechanical ventilation by using lung-protective strategies such as low tidal volume ventilation (LTVV):  


LTVV (6 mL/kg of ideal body weight) decreases the likelihood of overdistending alveoli and provoking barotrauma due to high plateau pressures (pressure applied to small airways and alveoli).  LTVV improves mortality in patients with ARDS.  In contrast, higher tidal volumes in ARDS may result in elevated pulmonary pressures due to the work of forcing larger volumes into stiff lungs (decreased compliance), leading to increased alveolar distension.


Providing adequate oxygenation:  


Increasing the fraction of inspired oxygen (FiO2) administered by the ventilator improves oxygenation; however, prolonged FiO2 levels >0.6 are associated with oxygen toxicity.  Increasing positive end-expiratory pressure (PEEP) also improves oxygenation by preventing alveolar collapse at the end of expiration, thereby decreasing shunting and the work of breathing.  Given the severe hypoxemia seen in ARDS, PEEP levels up to 15-20 cm H2O may be necessary to maintain oxygenation.  The goal is arterial partial pressure of oxygen (PaO2) at 55-80 mm Hg or peripheral saturation (SpO2) at 88%-95% (ie, preventing SpO2 <88%, not <92%) -.