The Science Journal of the American Association for Respiratory Care

2005 OPEN FORUM Abstracts

HIGH FREQUENCY POSITIVE PRESSURE VENTILATION (HFPPV) USING THE DRAGER EVITA XL VENTILATOR

Mark Siobal BS RRT, Julin Tang MD MS, Respiratory Care Services San Francisco General Hospital, UCSF Department of Anesthesia.

Background: High frequency ventilation is an alternative method of mechanical ventilation that theoretically achieves the goals of lung protective ventilation by potentially preventing over distension injury, and cyclic recruitment and derecruitment shear injury to the lungs. Commonly used high frequency ventilators lack conventional ventilation mode capabilities thus requiring two separate ventilators to transition between conventional ventilation and high frequency ventilation. We bench tested the Drager XL Ventilator set to deliver HFPPV on a mechanical test lung.

Method: Using the Airway Pressure Release Ventilation mode with a 0.1 second time at high pressure and a 0.15 second time at low pressure (cycle frequency of 240 /min or 4 Hz), slope set to zero, delta pressures (Δ P)of 20, 30, 40, and 50 cm H2O above 10, 15, and 20 cm H2O PEEP were used to ventilate a single compartment of a Michigan TTL test lung (compliance set at 0.02 mL/ cm H2O), through a 7.0 mm ETT. A Ventrak 1550 Respiratory Mechanics Workstation with an auxiliary pressure port positioned between the distal end of the ETT and the test lung chamber (surrogate for simulated carinal pressure), and the flow sensor positioned between the proximal end of the ETT and the ventilator "Y" was used to record test lung ventilation parameters. Tidal volume measured by the ventilator and at the ETT connection (VTvent and VTaw), mean airway pressure (MAP), PIP, and PEEP, were recorded from the ventilator display and at the distal end of the ETT (MAPvent, MAPcar, PIPvent, PIPcar, PEEPvent, PEEPcar) were recorded.

Results: The mean ± STDEV of VTaw was 87 ± 2.0, 118 ± 1.2, 143 ± 0.6, and 161 ± 1.0 mL at Δ P of 20, 30, 40, and 50 cm H2O above PEEP at all settings. VTaw was 5.0%. 10.8%, 17.2%, and 29.6% lower than VTvent at each Δ P setting due to volume compression in the circuit. MAPvent correlated closely to MAPcar (r = .9958) at all settings. Indirect control of MAP was possible by incremental adjustment of Δ P and PEEP. Pressure amplitude measured at the distal end of the ETT (PIP-PEEPcar) was 81% to 88% lower than the pressure amplitude measured by the ventilator (PIP-PEEPvent) due to pressure attenuation across the ETT. High PEEP alarms occurred due to dynamic hyperinflation of the test lung when PEEP measured by the ventilator was > 6 above set PEEP. Low Pressure alarms occurred when target PIP could not be achieved.

Conclusion: HFPPV using the Drager XL Ventilator appears to be technically feasible. Further investigation and testing using different ETT diameters, cycle frequencies, circuit compliances, test lung variables, and triggered alarm conditions are necessary before implementation of this technique into the clinical setting can be safely recommended.
  Δ P 20 Δ P 30 Δ P 40 Δ P 50  Δ P 20 Δ P 30 Δ P 40 Δ P 50
PEEP 10 PEEP 10
MAPvent 17 22 27 33 PIP-PEEPvent 16 26 36 48
MAPcar 16 21 26 31 PIP-PEEPcar 3 4 5 6
PEEP 15 PEEP 15
MAPvent 22 26 32 38 PIP-PEEPvent 17 26 36 48
MAPcar 22 26 31 36 PIP-PEEPcar 3 4 5 6
PEEP 20 PEEP 20
MAPvent 27 31 37 43 PIP-PEEPvent 16 26 36 47
MAPcar 27 31 36 41 PIP-PEEPcar 3 4 5 6
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