Measurement of respiratory function: gas exchange and its clinical applications

Gas exchange is the main function of the lungs. Lungs have a large reserve for gas exchange. Oxygen and carbon dioxide diffuse along their partial pressure gradient across the alveolar–capillary membrane. Alveolar ventilation and pulmonary circulation are closely matched to provide efficient gas exchange in the lungs. Hypoxaemia often results from mismatch in ventilation–perfusion. Gas exchange can be impaired in various disease states. Measurement of the diffusing capacity for carbon monoxide (DLCO) provides estimation of the gas exchange function. A low DLCO indicates an impairment of oxygen transfer across the alveolar–capillary membrane. Based on the lung function tests one can assess the risks of perioperative pulmonary complications. Anaesthesia and surgery adversely affect pulmonary function, many of which adverse effects can be prevented.