PS-378 Impact Of Amplitude, Frequency And I:e Ratio On Tidal Volume In High Frequency Ventilation (vthf) Using Different Hybrid Neonatal Ventilators

Background and aims High frequency ventilation (HFV) is frequently used in both term and preterm newborns. Hybrid neonatal ventilators capable of both HFV and conventional ventilation are currently available with different mechanisms for generating the required high frequency oscillation. In HFV, carbon dioxide elimination is directly correlated with VThf. The aim of the current study was to describe the impact of changes in amplitude, frequency and inspiratory-expiratory ratio (I:E) on VThf using different hybrid neonatal ventilators. Methods Three different hybrid neonatal ventilators were tested: Drager Babylog® VN500, Acutronic Fabian and SLE 5000. Each ventilator was calibrated using a new disposable ventilator circuit with a Drager pneumatic test lung leaving the humidifier dry to standardise all measurements. The VThf measured by the device was recorded after the system stabilised for 3 min. Each experiment was done using 21% oxygen, 8 cm H 2 O of pressure and repeated 3 times with negligible differences between measurements. Results In this setting, there is an expected inverse relationship between frequency and achieved VThf in all devices when using maximum amplitude. All three ventilators were more efficient at lower frequencies achieving higher VThf. In the two ventilators that allow I:E modification, the 1:1 ratio achieves higher VThf than 1:2 ratio. This becomes more evident at lower frequencies and higher amplitudes. Conclusions In tested ventilators the highest impact on VThf was achieved with frequency reduction. When modifiable, an I:E ratio of 1:1 optimises VThf at higher amplitudes. Clinicians need to be aware of these characteristics for optimising ventilation strategy.