Bench Test of the Dräger Babylog 8000plus Neonatal Ventilator with Heliox Mixtures.

Background: Helium-oxygen (heliox) gas mixtures are of a lower density than air/oxygen mixtures. Inhalation of gas with a low-density such as heliox can reduce airway resistance. This enables improved ventilation and the potential to increase expiratory flow and to decrease lung hyperinflation and auto-PEEP. There are several studies documenting the beneficial effects for neonatal patients with heliox therapy. I sought to determine if the Dräger Babylog 8000plus ventilator could deliver heliox via the 50-psi air connection of the ventilator. Also, the feasibility of leaving the flow sensor in line to potentially enable patient triggering and synchrony, and the accuracy of the oxygen blender and analyzer in the presence of heliox. In addition, what technical difficulties might be encountered, due to the degree of inaccuracy in volumes measured by the hot wire anemometer flow sensor?

Methods: An 80/20-heliox mixture was connected via the 50-psi air inlet of the ventilator. The SIMV and A/C modes were utilized, pressures 20/5, r 30, 0.4 inspiratory time with heliox mixtures in 5-10% increments from 10/90 to 79/21. FiO₂ was measured externally with a Maxtec MaxO₂ electrochemical analyzer (Salt Lake City, Utah). Volumes were measured with the Novametrix Co₂smo plus Respiratory Mechanics Monitor (Wallingford CT), which contains software programmed for compensation of heliox mixtures. The hot wire flow sensor was left in line for all concentrations except 75/25 and 79/21, when the high minute alarm maximal threshold was breached (15 L/min) and could not be disabled.

Results: The Dräger Babylog 8000plus cycled consistently with all heliox mixtures. Once heliox concentrations reached 50/50 the ventilator flow sensor was no longer able to display any tidal volume on the test settings and the apnea alarm had to be disabled. When heliox concentrations reached 75/25 the flow sensor had to be removed enabling IMV ventilation only. The ventilator oxygen analyzer was within 1% of the external analyzer, but the blender was as much as 9% off causing audio and visual alarms, due to internal alarm limits of ± 4% of the internal oxygen analyzer. The ventilator flow sensor tidal volumes were either erroneous or unable to read any volumes, at all concentrations of heliox.

Conclusion: The Dräger Babylog 8000plus gas mixing system has a zero internal bleed flow, enabling heliox mixtures to be introduced through the 50 psi air inlet, without wasting gas and allowing consistent cycling of the ventilator. The ventilator oxygen analyzer is accurate, but has to be disabled to overcome the constant alarm condition caused by the disagreement between blender setting and FiO₂ delivered. The flow sensor can be left active to facilitate patient triggering and synchrony until the ventilator flow sensor measures exhaled minute volumes of 15 L/min. Tidal volume measurements by the ventilator flow sensor are erroneous or absent and a supplemental monitor such as the Co₂smo plus should be utilized. Once the flow sensor is removed, IMV ventilation with heliox can be provided. More research should be done evaluating the ability of the ventilator?s flow sensor to accurately detect neonatal triggering efforts with heliox gas mixtures.