Necrotizing tracheobronchitis following high-frequency ventilation: effect of lung deflation

A piglet model of acute respiratory failure was used to determine whether necrotizing tracheobronchitis (NTB) reported during high-frequency pneumatic flow interrupter (HFFI) ventilation could be minimized by a different ventilatory strategy. Twenty-one piglets (mean age 3.8 days, average weight 1.4 kg) were anesthetized with ketamine and given Pavulon prior to saline lung lavage. Femoral vessels were cannulated for measurements of blood pressures, arterial blood gases (ABG), and fluid administration. Airway pressures were measured 5 mm above the endotracheal tube tip. To allow for lung deflation, HFFI (10 Hz) was programmed to pause for 1 sec either 5 (HFFI5) or 12 times per min (HFFI12). Seven animals were assigned to each of the treatment groups and to a conventional mechanical ventilation (CMV) control. All animals were kept on 1.0 FIO2 with ventilators adjusted to maintain ABG (pO2 = 50-100 mmHg and pCO2 = 30-40 mmHg). After 6 h of ventilation, the animals were sacrificed and their lungs inflated with formalin to 40 cm H2O. Sections were obtained from trachea, carina, mainstem, and hilar bronchi. An airway injury score (AIS) was calculated after "blinded" microscopic evaluation. There was no difference in total AIS between CMV (2.4) and HFFI12 (8.6) but a statistically significant difference (p less than 0.05) existed between CMV and HFFI5 (14.1). NTB was limited to the trachea during HFFI12 but extended down to the hilar bronchi during HFFI5. More frequent lung deflations reduce the severity and distribution of NTB during HFFI ventilation.