Introduction: Mechanical ventilation of intubated patients is standard to meet oxygenation and ventilation goals. This can require significant energy and oxygen resources. In military operations and mass casualty disasters, oxygen conserving strategies may be important. Low flow tracheal insufflation of oxygen (TRIO) is a technique that provides adequate oxygenation while conserving oxygen during apnea. This technique, however, is limited by increases in carbon dioxide (CO2) when used for extended periods. The addition of passive pressure release ventilation could potentially improve CO2 elimination and the acceptance of this technique. The purpose of this study was to determine whether TRIO combined with the novel configuration of a portable ventilator used to provide passive pressure release ventilation improves CO2 levels during apneic oxygenation.
Methods: Animals (n = 7) were anesthetized, paralyzed, and intubated. Oxygen (O2) was insufflated through the capillary lumen of the Boussignac endotracheal tube at 2 L/min. The low flow O2 was the only source of power and gas for ventilation. A modified Oxylator EMX transport ventilator connected to the endotracheal tube was configured to release when pressure in the subjects lungs reached 30 cm H2O. No electrical or pneumatic sources were required. Hemodynamic measurements and arterial blood gases were taken at various intervals for 2 hours.
Results: All pigs remained adequately oxygenated with Pao2 >390 mm Hg in all subjects at every blood gas measurement and survived the 2-hour experiment. Baseline Paco2 (43 ± 4 mm Hg) increased and pH (7.48 ± 0.03) decreased to 72 ± 5 mm Hg and 7.29 ± 0.02 at 1 hour and 83 ± 8, 7.24 ± 0.03 at 2 hours. This is significantly less than would be expected during apnea over this time period. Hemodynamic measurements remained stable.
Conclusion: The combination of low flow TRIO with a modified Oxylator in this novel configuration provides acceptable Pao2, Paco2, and hemodynamic parameters for 2 hours in apneic swine. This could be a valuable technique in situations where oxygen and power are limited.
From the Brooke Army Medical Center (I.H.B., J.A.L., K.W.G.); and San Antonio Uniformed Services Health Education (J.A.L.), Consortium, San Antonio, Texas.
Submitted for publication May 9, 2007.
Accepted for publication December 31, 2007.
The opinions or assertions contained herein are the private views of the authors and are not to be constructed as official or reflecting the views of the Department of the Army or the Department of Defense.
Address for reprints: Ian H. Black, MD, Brooke Army Medical Center, Department of Anesthesiology and Operative Services, 3851 Roger Brooke Drive, Fort Sam Houston, TX 78234; email: firstname.lastname@example.org.