Day 2 - ARDS
Clinical spectrum of disease defined by the Berlin Criteria:
Acute onset - should have occurred within 1 week of known ARDS insult
Bilateral involvement - bilateral opacities on CXR in an alveolar pattern, generally patchy with peripheral predominance
Absence of alternative cause - should not be related to cardiac failure or volume overload
Significant hypoxia - Arterial PO2/Fio2 <300 on at least 5cm H20 of PEEP (on non-invasive or invasive mechanical ventilation). Think of it as the fraction of oxygen getting into the blood compared to the amount of oxygen being delivered to the patient.
Severity is graded using PO2/Fio2 ratio:
Mild: 200 mm Hg < PaO2/FIO2 ≤ 300 mm Hg
Moderate: 100 mm Hg < PaO2/FIO2 ≤ 200 mm Hg
Severe: PaO2/FIO2 ≤ 100 mm Hg
Management:
Focused on the treatment of the underlying inflammatory trigger, optimization of the patient’s respiratory distress, and preventing further damage to the lungs.
High PEEP - props open collapsed alveoli, promoting improved oxygenation and decreasing shunting, prevents ventilator-associated lung injury by preventing atelectrauma & can help reduce the degree of required FiO2.
Low Tidal Volumes - helps prevent volutrauma. Target 6mL/kg/min Ideal Body Weight (not actual weight). ARMA trial demonstrated 11% absolute risk-reduction in mortality.
Recruitment Maneuvers - practice of delivering a high level of CPAP (i.e., 30-40cm H20 for 40 seconds) to open collapsed alveoli.
Prone Positioning - decreases collapse in the areas of the lung posterior to the heart & can improve V/Q mismatch. PROSEVA trial demonstrateed absolute risk-reduction of 16% with prone positioning.
Other strategies include avoidance of volume overload, consideration of corticosteroids and paralytics in severe cases.
ROSE trial from PETAL group demonstrated no mortality difference with early administration of neuromuscular blockade.
Benefit of ECMO remains unclear, but often used as salvage measure in severe refractory ARDS.
