Reflex airway reaction to fluid aspiration

¹ Department of Medicine, University of Sydney, Sydney, Australia

The mechanism of the lung mechanics changes after fluid aspiration was investigated in sheep, intubated and lightly anesthetized with thiopentone. The increase in venous admixture after intratracheal injection of fluid while breathing 100% oxygen indicated airway closure as the explanation for the associated gross fall in lung compliance (Cl). Atropine sulfate reduced the Cl fall produced by 1 ml/kg body wt. of fluid to a significantly greater extent than prior vagotomy. In vagotomized animals the reaction to fresh water was potententiated by prostigmine. A nonfoaming fluid with a surface tension of 27 dynes/cm had the same effect as fresh water. The reaction to water was not affected by lysergic acid butanolamide or aerosol tetracaine. Intravenous or aerosol isoproterenol reduced the Cl fall after water. These findings show that fluid aspiration invokes a reflex response of the parasympathetic nervous system, with both central and peripheral components producing closure of lung units. The relation of this reflex to other respiratory reflexes is discussed. When inflation alone was ineffective or lead to deterioration, both atropine and isoproterenol helped to reverse the effects of sea and fresh water.