A comparison of intratracheal pulmonary ventilation to conventional ventilation in a surfactant deficient animal model

Objective: To compare intratracheal pulmonary ventilation (ITPV) with conve ntional ventilation in a rabbit model of surfactant deficiency. Design: A prospective randomized animal study. Setting: The Children's National Medical Center Research Animal Facility in Washington, DC. Subjects: Adult male New Zealand white rabbits (n = 20), weighing 1.4-4.2 k g. Interventions: After anesthesia and catheter placement, rabbits were trache otomized, paralyzed, and placed on the conventional ventilator. We determin ed pulmonary functions at baseline. We washed surfactant out of the lungs b y using serial bronchoalveolar lavages. Pulmonary function studies were det ermined after completion of the bronchoalveolar lavages and were used as an indication of severity of lung injury. Animals were randomized into two gr oups: We placed ten animals on ITPV, using the ITPV reverse thruster cathet er designed by Kolobow and a prototype ITPV ventilator designed at Children 's National Medical Center; we placed ten animals on conventional ventilati on using the Sechrist iv-100 ventilator. Arterial blood gases were drawn ev ery 15 mins, and the ventilator settings were adjusted to the minimal level that would maintain arterial blood gases in the following ranges: pH 7.35- 7.45, PaCO2 30-40 torr (3.99-5.33 kPa), PaO2 50-70 torr (6.66-9.33 kPa), An imals were ventilated with the randomized ventilation techniques for 4 hrs. Measurements and Main Results: Peak inspiratory pressure, mean airway press ure, and positive end-expiratory pressure were measured at the distal end o f the endotracheal tube. We recorded these variables plus respiratory rate at baseline and every 30 mins for a total of 4 hrs of ventilation. Lung com pliance did not differ between groups at the postlavage study period (ITPV, 0.56 +/- 0.13 mL/cm H2O/kg; conventional 0.49 +/- 0.15 mL/cm H2O/kg). At t he end of the 4 hr study period, peak inspiratory pressure (ITPV, 26.2 +/- 4.6 cm H2O; conventional, 32.4 +/- 5.04 cm H2O, p = .007) and positive end- expiratory pressure (ITPV, 3.9 +/- 1.96 cm H2O; conventional, 6.3 +/- 1.42 cm H2O, p = .005) were lower in the ITPV ventilation group. Peak inspirator y pressure was significantly lower in the ITPV group by 2 hrs into the stud y. Conclusion: In this model of surfactant deficiency lung injury, ventilation and oxygenation were achieved at significantly lower ventilator settings u sing ITPV compared with conventional ventilation. Long-term studies are nee ded to determine whether this reduction in ventilation is maintained, and i f so, if lung injury is reduced.