The use of specific aerosol therapy in patients on mechanical respiratory support should be considered in accordance with other systemic effects. This study points up the hemodynamic, respiratory, and ventilatory effects of each of three agents: saline, isoproterenol, and racemic epinephrine.Contrary to the opinion that saline has a placebo effect, aerosol saline therapy decreased oxygen consumption, oxygen transport, oxygen utilization coefficient, and effective dynamic compliance.