Multisystem Organ Failure, Lung Dysfunction in

200,000 new cases of ARDS occur annually in USA.

0.2% of general surgical pts develop ARDS postop.

Hypoxemia, hypercarbia, hemodynamic instability.

ARDS hypoxemia requires ventilator management using high PEEP to achieve adequate oxygenation.

High PEEP may impede right atrial/right ventricular preload.

Lower RV preload can reduce stroke volume and cardiac output. This can lead to alveolar hypoperfusion, thus inhibiting carbon dioxide elimination and further worsening hypercarbia and respiratory acidosis.

Mechanical ventilation modes, such as inverse ratio and pressure control, target oxygenation rather than carbon dioxide elimination, resulting in permissive hypercarbia.

Mechanical ventilation may cause breath stacking, which can also cause hemodynamic instability.

Acidosis and dysrhythmias worsen hemodynamic instability.

Mortality: 40% among ARDS alone; >90% for MODS, involving three or more organ failures.

Poor prognostic factors: Advanced age, impaired immunity, poor prior functional status, resistant organisms, MODS despite adequate therapy.

Severity of ARDS by Berlin criteria as graded by oxygenation ratio (PaO ₂ /FiO ₂ ): Mild ≤300 mm Hg; moderate ≤200 mm Hg; severe ≤100 mm Hg.

Lung dysfunction in MODS is either ARDS or ALI.

ARDS is more severe than ALI.

MODS exists when altered organ function in the acutely ill requires medical intervention for homeostasis.

Pulm conditions (pneumonia, lung contusion)

Nonpulmonary (sepsis, trauma, transfusions, pancreatitis, DIC)