PULMONARY GAS EXCHANGE



The arterial blood gas values are determined by the gas composition in the alveoli and its suc­cessful equilibration with the blood in the pul­monary capillaries. The Po2 and Pco2 in the al­veoli, in turn, are determined by the inspired gas tensions, the mixed venous Po2 and Pco2, the total ventilation and blood flow, and most importantly the success with which the lung is able to match ventilation and blood flow. Abnormality of any of these factors leads to hypoxemia arid/or hy-percapnia. For convenience they are grouped into four basic mechanisms.