Respiratory Failure

Abstract

Normal respiratory function keeps the arterial blood almost fully oxygenated and the arterial carbon dioxide pressure within a narrow range, both at rest and on the most extreme exertion. We can therefore define respiratory failure in terms of arterial blood gases as 'a fall in arterial oxygen saturation or a rise in arterial carbon dioxide pressure beyond the normal range'. We must, however, exclude three factors which may cause alterations in blood gases in the absence of respiratory failure. These are: (1) Anatomical shunting of blood past the lungs as in a right-to-left shunt in the heart. (2) Metabolic alkalosis in which, when compensated, the arterial pCO2 is increased. (3) Lowering of the ambient oxygen tension, as at high altitude.