Hybrid Intratracheal Pulmonary Ventilation on the Changes of Dead Space/Tidal Volume Ratio in Rabbits / 대한마취과학회지

ABSTRACT

BACKGROUND: Intratracheal pulmonary ventilation (ITPV) is a form of tracheal gas insufflation which enhances the clearance of CO2 from dead space and lungs by a bias gas through a reverse thrust catheter (RTC). After exiting from the catheter tip in the distal trachea, the flow of gas is directed outward away from the lungs. Gas is intermittently re-directed into the lung as a tidal volume by a valve on the expiratory circuit. Hybrid ITPV (hITPV) is a continuous flow ventilatory technique that adopts inspiratory fresh gas from a ventilator and RTC. We hypothesized that hITPV might reduce the dead space/tidal volume ratio as compared with volume controlled ventilation (VCV). METHODS: VCV and hITPV were compared in 6 tracheostomized rabbits. We aimed at maintaining normal partial pressure of arterial CO2 (PaCO2) and minute CO2 clearance (VCO2) while the respiratory rate (RR) was set at 20, 40, 80 or 120/min with an inspiratory to expiratory (I : E) ratio of 1 : 2 or 1 : 1. Blood pressure and airway pressures were monitored and the dead space ratio was calculated. RESULTS: PaCO2, VCO2 and alveolar ventilation were statistically constant with various RR with the same I : E ratio during VCV and hITPV. Mean values of PaO2 were higher than 400 mmHg during the experiment. VT, VD and PIP were lower in hITPV than in VCV under I : E ratios of 1 : 2 and 1 : 1 at the same RR. The VD/VT ratios at an I : E ratio of 1 : 2 were 0.66 +/- 0.07, 0.74 +/- 0.05, 0.81 +/- 0.04, and 0.83 +/- 0.04 during VCV and 0.44 +/- 0.15, 0.56 +/- 0.10, 0.64 +/- 0.08 and 0.67 +/- 0.06 during hITPV at an RR of 20, 40, 80 or 120/min, respectively. The VD/VT ratios at an I : E ratio of 1 : 1 were 0.71 +/- 0.07, 0.73 +/- 0.04, 0.80 +/- 0.04, and 0.83 +/- 0.03 during VCV and 0.50 +/- 0.07, 0.54 +/- 0.10, 0.63 +/- 0.10, and 0.70 +/- 0.08 during hITPV at an RR of 20, 40, 80 or 120/min, respectively. The VD/VT ratio was reduced by the institution of hITPV. CONCLUSIONS: It was concluded that hITPV could be applied to minimize the airway pressures and dead space resulting from VCV.