Abstract
Background The Dräger Babylog 8000 ventilator calculates the delivered pressure from inspiratory and expiratory transducers. It alarms “pressure out of range” when the difference between the transducer exceeds 20 cm H2O in at least 20 of 30 measurements during the most recent second. To provide a neonatal ventilator circuit that delivers optimal temperature and humidity with no condensation in the inspiratory or expiratory limb Fisher and Paykel developed a dual heated neonatal breathing circuit No. RT235 (Dry Circuit). However the resistance of this circuit during high frequency ventilation (HFOV), when the circuit flow may rise to 30 L/min, causes alarms at certain ventilatory settings. These alarms rarely occurred with conventional circuits in our NICU.
Aim To find the mean airway pressure, frequency and amplitude at which the Dräger 8000 plus ventilator alarmed “pressure out of range” when used in HFOV mode with the Dry Circuit.
Methods Laboratory studies used the ventilator in HFOV mode with the F&P Dry Circuit attached to an MR290 humidifier chamber at 37oC with the circuit at 40oC. At a set mean airway pressure (MAP) the frequency and amplitude were altered from minimum to maximum and the settings where the “pressure out of range” alarmed were recorded. 6000 combinations of all pressures and frequencies were studied. These were repeated with the 36cm inspiratory extension removed from the circuit.
Results: The results are shown in the table, for frequencies from 5 to 20 Hz and MAP from 5 to 25 cm H2O. Loud speaker symbol indicates settings where the alarm sounded. The ventilator cannot be used at those settings with this circuit. It did not alarm at settings with no loud speaker symbol. Changing amplitude at any MAP and frequency combination did not cause the alarm. Removing the inspiratory extension tube did not alter the MAP and frequency combinations where the alarm sounded.
Conclusion: The F&P Dry Circuit can be used with the Dräger Babylog 8000 in HFOV mode at some MAP and frequency settings and not at others. This table can help clinicians decide which HFOV MAP frequency combinations can be used.
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Morley, C., Mishra, U. 192 Investigations of The F & P Neonatal Dry Ventilator Circuit in High Frequency Mode on the Dräger 8000 Plus Ventilator. Pediatr Res 56, 496 (2004). https://doi.org/10.1203/00006450-200409000-00215
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DOI: https://doi.org/10.1203/00006450-200409000-00215