Acute Respiratory Distress Syndrome (ARDS)

A patient with ARDS may remain profoundly hypoxaemic even while receiving a high inspired oxygen concentration. The problem is not simply narrowed airways: inflammatory injury has filled and collapsed alveoli, so blood continues passing through poorly ventilated regions. This creates an intrapulmonary shunt and explains why increasing oxygen alone may produce less improvement than expected. The pattern is acute respiratory deterioration after an identifiable insult, diffuse bilateral opacities, and oxygenation failure that cannot be explained entirely by left-sided heart failure or fluid overload. The nurse watches the oxygen requirement, work of breathing, blood gases, and ventilator pressures together. A falling oxygen saturation with rising FiO2 is a change in trajectory, not just another abnormal vital sign.