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

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.

The Ventilatory Effect of Hybrid Ventilation in Rabbits

PURPOSE: Intratracheal pulmonary ventilation (ITPV) is developed to decrease dead space ventilation. A reverse thrust catheter (RTC) is introduced into an endotracheal tube through an adapter. Bias gas through the RTC exits from the catheter tip. The flow of gas is redirected outward away from the lung. Gas is intermittently introduced into the lung as tidal volume (VT) by an expiratory valve. ITPV can be combined with pressure control mode, resulting in hybrid ventilation (HV). We hypothesized that HV might decrease VT, compared with volume controlled ventilation (VCV) or pressure controlled ventilation (PCV) alone. METHODS: HV was compared with VCV and PCV in 7 tracheostomized rabbits. We aimed at maintaining PaCO2 levels normal as the respiratory rates (RR) were set at 20, 40, 80, and 120/min. Blood pressure and airway pressures were monitored and dead space ratio was calculated. RESULTS: The dead spaces (VD) of VCV are 30+/-4 mL, 18+/-4 mL, 14+/-4 mL, and 12+/-5 mL and the VD of PCV are 24+/-6 mL, 16+/-3 mL, 15+/-4 mL and 12+/-4 mL at the respiratory rates of 20/min, 40/min, 80/min, and 120/min, respectively. The VD of HV are 13+/-6 mL, 9+/-3 mL, 7+/-2 mL, and 5+/-1 mL, respectively. The VT and PIP of HV are significantly lower than those of VCV and PCV at the same RR. CONCLUSION: It can be concluded that HV can be applied to minimize the airway pressures and dead space ventilation of VCV and PCV.

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.

The Effect of Intratracheal Pulmonary Ventilation on Dead Space and Airway Pressures in Rabbits with Acute Respiratory Failure Induced by Oleic Acid Injection / 대한마취과학회지

BACKGROUND: Intratracheal pulmonary ventilation (ITPV) was developed to allow a decrease in physiological dead space during mechanical ventilation. To reduce anatomic dead space, a reverse thrust catheter (RTC) is introduced into an endotracheal tube (ETT) through an adapter and positioned just above the carina inside the ETT. ITPV can be combined with pressure control mode of mechanical ventilation to make hybrid ventilation(HV). The effect of HV on the reduction of dead space was compared with that of conventional mechanical ventilation(CMV) in rabbits with acute respiratory failure. METHODS: Oleic acid of 0.06 ml/kg was injected to induce acute respiratory failure in 7 rabbits. PaO2 and PaCO2 were measured 30 minutes after the injection. Oleic acid was injected in another 7 rabbits to compare CMV with HV while increasing the respiratory rate(RR). Tidal volume, dead space(VD) and peak inspiratory pressure(PIP) were measured at the same RR. RESULTS: PaO2 decreased significantly from 467+/- 68 mmHg to 156 +/-26 mmHg at FIO2 1.0 after the injection of oleic acid. In another 7 rabbits, the VD's of CMV were 34+/- 10 ml, 27 +/-10 ml, 20+/- 6 ml, and 18+/- 3 ml at respiratory rate of 20/min, 40/min, 80/min and 120/min, respectively. The VD's of HV were 28 +/-11 ml, 16+/- 8 ml, 9+/- 4 ml, and 7+/- 3 ml at the same respiratory rates as in CMV. The VD's of HV were lower than those of CMV. The PIP's were lower in HV than in CMV. CONCLUSION: We conclude that HV, as the modification of ITPV, can be applied to acute respiratory failure to minimize the airway pressures and dead space of CMV.