A Comparison of Pressure Controlled Ventilation and Hybrid Ventilation in Rabbits

Lee, Kook Hyun; Rhee, Ka Young; Lee, Sang Chul

Abstract

BACKGROUND: Intermittent positive pressure is required to overcome pulmonary airway resistance during inspiration and to deliver an adequate tidal volume. Previous animal experiments have shown that mechanical ventilation may worsen the lung injury when high airway pressure and large tidal volume are required to achieve adequate ventilation and oxygenation. Many ventilatory strategies have been developed to minimize airway pressure increase for the less compliant lung. Intratracheal pulmonary ventilation (ITPV) was developed to allow a decrease in physiological dead space during mechanical ventilation.
METHODS
Pressure controlled ventilation (PC) has been compared with hybrid ventilation (HV) which consists of PC and ITPV in 7 rabbits. A reverse thrust catheter (RTC) was introduced into an endotracheal tube (ETT) through an adapter and positioned just above the carina inside the ETT. Fresh gas flowed continuously along the gap between inner cannula and outer cap in the expiratory direction. Gas was intermittently re-directed into the lung as a tidal volume by a valve on the expiratory circuit with ventilatory mode of PC to make HV. Peak inspiratory pressure (PIP) and dead space (VD) at various respiratory rates (RR) of 20/min, 40/min, 80/min and 120/min were compared between PC and HV while maintaining normal PaCO2.
RESULTS
The PIPs of PC were 12.4 +/- 3.4 cmH2O, 9.0 +/- 2.7 cmH2O, 8.8 +/- 2.7 cmH2O, and 7.6 +/- 2.5 cmH2O at RR of 20/min, 40/min, 80/min and 120/min, respectively. The PIPs of HV were 9.2 +/- 3.2 cmH2O, 6.2 +/- 1.7 cmH2O, 5.0 +/- 2.0 cmH2O, and 4.5 +/- 1.8 cmH2O at the same RR of 20/min, 40/min, 80/min and 120/min, respectively. The VDS of HV were lower than those of PC.
CONCLUSION
It can be concluded that ITPV can be applied as a HV to minimize airway pressure under the setting of PC.