Regional tracheal blood flow during conventional and high-frequency jet ventilation in suckling pigs

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 during ventilation.

Prospective, multiple group, controlled experimental study.

Medical school research laboratory.

Twenty, 3- to 5-wk-old suckling pigs.

Anesthetized, closed-chest piglets were intubated and ventilated for 30 mins with conventional mechanical ventilation and then ventilated for 2 additional hrs with either conventional mechanical ventilation or high-frequency jet ventilation. Groups were also ventilated, using both modes of ventilation, with either 37 degrees C humidified gas or 25 degrees C dry gas.

Blood flow groups were compared during spontaneous breathing, conventional mechanical ventilation, high-frequency jet ventilation and both ventilation modes, using 37 degrees C humidified or 22 degrees C dry inspired gas. Groups were compared, using an analysis of variance with a Newman-Keul's post-test. Regional tracheal blood flow was measured, using radioactive microspheres. Cardiac output and organ blood flows were also monitored. Tracheal blood flow increased 10.3-fold within 30 mins after intubation, but there were no significant differences in regional or total tracheal blood flow between conventional mechanical ventilation and high-frequency jet ventilation, using 37 degrees C humidified gas. Tracheal blood flow was increased further using high-frequency jet ventilation and 25 degrees C dry gas but not conventional mechanical ventilation with dry gas. Although ventilation reduced cardiac output by approximately 30%, there were no significant differences in organ distribution between modes of ventilation.

Acute tracheal hyperemia occurred with intubation and ventilation with both conventional mechanical ventilation and high-frequency jet ventilation but no differences were observed between ventilation modes. Hyperemia was further increased with cool, dry inspired gas, using high-frequency jet ventilation but not conventional mechanical ventilation. Although acute tracheal ischemia was not produced by high-frequency jet ventilation or conventional mechanical ventilation, factors which alter the balance between arterial supply and metabolic demand or induce inflammation may contribute to the tracheal necrosis reported during sustained ventilation.