Haitsma Lungprotective Ventilation in Ards

before the work of Asbaugh’s group, von Neergaard 2 in 1929 was the first to suggest that surface tension plays a role in lung elasticity. He showed that the pressure necessary to fill the lung with liquid was less than half the pressure needed to fill the lung with air. His explanation for this remarkable difference was based on the assumption that at the interface of each alveolus there must be some retraction forces between air and fluid. This retraction force could reduce the size of the alveolus according to the law of Laplace.2 From the law of Laplace, P = 2γ/r (P = pressure in the bubble; γ = surface tension; r = radius of the bubble), it could be concluded that a reduction of the radius of a bubble needs an equal reduction in surface tension to keep the bubble stable, which can only be accomplished by a dynamic behavior of a surface tension lowering material, which is pulmonary surfactant. Thus, when the endogenous surfactant system is impaired, independent of the cause, the rise in surface tension will result in atelectasis formation, enlargement of the functional right-to-left shunt, pulmonary edema, impaired gas exchange and subsequent hypoxemia.3 These patients require mechan-