Acute Respiratory Distress Syndrome

Etiology

Rapid progression of acute respiratory failure characterized by noncardiogenic pulmonary edema causing severe hypoxemia that is refractory to usual oxygen thereapy

Pathophysiology

increase in the permeability of alveolar-capillary membrane due to a variety of injuries

Decreased aerated lung tissue

Impaired gas exchange

Decreased lung compliance

Increased pulmonary vascular resistance

Pulmonary arterial pressures

Clinical signs and symptoms

Acute onset (within 1 week of known clinical upset)

Bilateral infiltrates consistent with pulmonary edema

Pulmonary edema not due to cardiac failure or fluid overload - no clear cause

Refractory hypoxemia

Differential Diagnostics

Diagnostics

cardiogenic pulmonary edema

New and/or worsening respiratory symptoms

Signs and symptoms of respiratory distress

Diffuse crackles on auscultation

Signs and symptoms of hypoxemia

ABGs: P/F ratio < 100

CXR or CT findings of diffuse bilateral infiltrates showing a "ground glass" appearance

BNP to rule out CHF

CVP to rule out overhydration

Lab data to rule out sepsis: CBC, blood and urine cultures, blood lactate

Respiratory Management

Intubation and mechanical ventilation: Vt 6 - 4 mL/Kg IBW

Goal of plateau pressures at or below < 30 cmH2O

I:E ratio 1:2 or 1:3

Set minute ventilation with rate to achieve ~ 7 - 9 L/min

Titrate PEEP and FiO2 to maintain PaO2 55 - 80 mmHg and SaO2 88 - 95%

Maintain pH at or above 7.20 and PaCO2 allowed to rise (permissive hypercapnia)

Medications: inhaled nitric oxide (iNO) and Flolan