REGIONAL TRACHEAL BLOOD-FLOW DURING CONVENTIONAL AND HIGH-FREQUENCY JET VENTILATION IN SUCKLING PIGS

Objective: To determine whether intubation and ventilation with either conventional mechanical ventilation or high-frequency jet ventilation , using dry or humidified gas, could induce regional tracheal ischemia and serve as a basis for the tracheal necrosis observed clinically du ring ventilation. Design: Prospective, multiple group, controlled expe rimental study. Setting: Medical school research laboratory. Subjects: Twenty, 3- to 5-wk-old suckling pigs. Interventions: Anesthetized, cl osed chest piglets were intubated and ventilated for 30 mins with conv entional mechanical ventilation and then ventilated for 2 additional h rs with either conventional mechanical ventilation or high frequency j et ventilation. Groups were also ventilated, using both modes of venti lation, with either 37 degrees C humidified gas or 25 degrees C dry ga s. Measurements and Main Results: Blood flow groups were compared duri ng spontaneous breathing, conventional mechanical ventilation, high fr equency jet ventilation and both ventilation modes, using 37 degrees C humidified or 22 degrees C dry inspired gas. Groups were compared, us ing an analysis of variance with a Newman-Keul's post test. Regional t racheal blood flow was measured, using radioactive microspheres. Cardi ac output and organ blood flows were also monitored. Tracheal blood fl ow increased 10.3-fold within 30 mins after intubation, but there were no significant differences in regional or total tracheal blood flow b etween conventional mechanical ventilation and high-frequency jet vent ilation, using 37 degrees C humidified gas. Tracheal blood flow was in creased further using high-frequency jet ventilation and 25 degrees C dry gas but not conventional mechanical ventilation with dry gas. Alth ough ventilation reduced cardiac output by similar to 30%, there were no significant differences in organ distribution between modes of vent ilation. Conclusions: Acute tracheal hyperemia occurred with intubatio n and ventilation with both conventional mechanical ventilation and hi gh frequency jet ventilation but no differences were observed between ventilation modes. Hyperemia was further increased with cool, dry insp ired gas, using high-frequency jet ventilation but not conventional me chanical ventilation. Although acute tracheal ischemia was not produce d by high-frequency jet ventilation or conventional mechanical ventila tion, factors which alter the balance between arterial supply and meta bolic demand or induce inflammation may contribute to the tracheal nec rosis reported during sustained ventilation.