The Effect of Intratracheal Pulmonary Ventilation on the Decrease of Dead Space in Rabbits with Acute Respiratory Failure / 대한마취과학회지

BACKGROUND: A technique that improves the efficiency of alveolar ventilation should decrease the pressure required and reduce the potential for lung injury during mechanical ventilation. High PaCO2 can be permitted to lower airway pressures as in permissive hypercapnia (PH). Intratracheal pulmonary ventilation (ITPV) was developed to allow a decrease in physiological dead space during mechanical ventilation. We compared the effect of hybrid ventilation (HV) as a modification of ITPV with PH on the decrease of tidal volume and airway pressures in rabbits with acute respiratory failure. METHODS: Tracheostomy was performed in 7 rabbits ventilated under volume-controlled mode in the supine position. Arterial blood gas analysis, airway pressures, and dead space ventilation were measured at respiratory rate of 20/min as control values. Oleic acid (OA) of 0.06 ml/kg was injected to induce acute respiratory failure. Tidal volume (VT) was elevated to maintain PaCO2 in the normal range. The same parameters were measured as OA values. Then VT was reduced to the control level to allow PH. HV was initiated by inserting a reverse thrust catheter (RTC) into the endotracheal tube. HV consists of a pressure-controlled mode of mechanical ventilation and ITPV while flushing fresh gas continuously via the RTC. Respiratory parameters were compared under control, OA, PH and HV conditions. RESULTS: Oleic acid injection decreased PaO2 from 401+/-35 mmHg to 129+/-39 mmHg, increased VT from 42+/-5 ml to 52+/-10 ml, and increased VD/VT ratio from 0.65+/-0.07 to 0.71+/-0.07. During PH, the increase in PaCO2 was accompanied by the increase in VD/VT ratio from 0.71+/-0.07 to 0.79+/-0.03 and by the decrease of peak inspiratory pressure (PIP) from 19.4+/-4.0 cmH2O to 16.8+/-3.1 cmH2O. PaCO2 was lowered from 50+/-5 mmHg in PH to 39+/-5 mmHg in HV with a lower VT. VD/VT ratio in HV was as low as that in control. CONCLUSION: HV is an effective and easy-to-use ventilatory modality to reduce PaCO2 and airway pressures by the reduction in VD/VT ratio in acute respiratory failure model.

A Comparison of Pressure Controlled Ventilation and Hybrid Ventilation in Rabbits / 대한마취과학회지

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.