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The effects of surfactant on haemodynamics in hyaline membrane disease

Artificial surfactant was first used to treat infants with hyaline membrane disease (HMD) by Chu et al 30 years ago.1 Benefit was measured by an increase in respiratory compliance in 34 of 43 (79%) occasions, but these effects were overshadowed by those of the pulmonary vasodilator, acetyl choline. In this group of acidotic and hypoxaemic babies, acetyl choline improved blood gas status and reduced total right-to-left shunting; surfactant did not. The authors concluded that “pulmonary ischaemia” was more important than surfactant deficiency in the pathogenesis of HMD. Most now believe that surfactant deficiency is the major aetiological factor, and latterly exogenous surfactant treatment has significantly improved the outlook of babies with severe HMD.2 

In the modern intensive care setting surfactant instillation rapidly improves respiratory gas exchange—very different from 30 years ago. There may, however, be a price to pay for such rapid changes in respiratory function. Surfactant instillation is often associated with dramatic haemodynamic changes, although studies have shown contradictory effects. Cerebral blood flow increases3 4and decreases, perhaps by up to 36%5; such changes may be associated with an increased incidence of intraventricular haemorrhage and periventricular leucomalacia.6 Similarly, studies of pulmonary arterial pressure (PAP) and pulmonary blood flow have also shown contradictory effects. Two groups who observed a fall in PAP have claimed that a primary action of surfactant is to increase total pulmonary blood flow7 8; but another group reported no fall in PAP.9 

The effect of surfactant on effective pulmonary blood flow (the proportion of blood perfusing ventilated alveoli) is also still uncertain. Chu et al 1 and a recent study using Curosurf10 demonstrated no effect on effective pulmonary blood flow despite a considerable improvement in oxygenation. Nevertheless, further recent research has prompted the conclusion that effective …