This may occur in adults as ACUTE RESPIRATORY DISTRESS SYNDROME (ARDS), or in newborn children, when it is also known as HYALINE MEMBRANE DISEASE. The adult syndrome consists of PULMONARY OEDEMA of non-cardiac origin. The process begins when tissue damage, often secondary to SEPTIC SHOCK, stimulates the autonomic nervous system; releases vasoactive substances; precipitates COMPLEMENT activation which causes white cells to lodge in the pulmonary capillaries where they release substances which damage the lining of these vessels; and produces abnormalities of the clotting cascade – the serial process that leads to clotting of the blood (see COAGULATION).

Respiratory distress syndrome is a complication of SHOCK, systemic SEPSIS and viral respiratory infections. It is a serious disease with a mortality of more than 50 per cent. The maintenance of adequate circulating blood volume, peripheral PERFUSION, acid-base balance and arterial oxygenation is important, and assisted ventilation should be instituted early.

In newborns the mechanism is different, being provoked by an inability of the lungs to manufacture SURFACTANT. It is largely a condition of premature infants, beginning a few hours after delivery, characterised by rapid breathing with indrawing of the spaces between and below the ribs and grunting on breathing out. Because of the lack of surfactant, the lungs are stiff, so difficult to inflate and tend to collapse at the end of each expiration so that greater effort than normal is necessary to reinflate them. Oxygen therapy is usually needed, with careful monitoring because of the danger of OXYGEN TOXICITY and many of these babies require artificial ventilation for days or even weeks.