The Science Journal of the American Association for Respiratory Care

2008 OPEN FORUM Abstracts

COMPARISON OF AIRWAY RESISTANCE CALCULTIONS DURING MECHANICAL VENTILATION OF A TEST LUNG MODEL UTILIZING TWO DIFFERENT INSPIRATORY FLOW PROFILES

Lindsey Rash1,2, Lori Boylan1,2, David Horney1,2, Joseph Ciarlo1.2, Tom Blackson1,2



Background: Many RC departments incorporate airway resistance (Raw) calculations into assessment based protocols for ventilator patient liberation. Airway resistance calculations during volume controlled ventilation (VCV) have traditionally been performed using a constant flow profile. The LTV-1200 ventilator incorporates a decelerating flow profile as the sole option during VCV. The purpose of this study was to determine if airway resistance calculations performed using the LTV-1200 ventilator with a decelerating flow waveform provide data consistent with that from the Drager XL (DXL) ventilator which utilizes a constant flow profile.

Materials & Methods: We conducted a bench study comparing calculated inspiratory airway resistances when utilizing an LTV-1200 versus a DXL to ventilate a Michigan test lung. VT (0.5 L), f (12/min) and compliance (0.04 L/cm H2O), remained constant for all test conditions. Raw was varied using parabolic resistors #5, #20, and #50 in conjunction with three separate inspiratory times, 0.5, 0.7, and 1.0 seconds. VT, PIP, PPLAT, PEEP, and peak flow were recorded using each ventilators monitoring system. Raw calculations were averaged over five consecutive breaths. The equation used to calculate Raw with the DXL was (PIP-PPLAT/set flow), and (PIP-PPLAT/calculated flow) for the LTV-1200.

Results: The airway resistances calculated from the LTV trials were significantly lower than the airway resistances calculated during the DXL trials under all test conditions, (p < 0.01).

Conclusion: The calculation of Raw varies significantly when a constant flow versus a decelerating flow profile is used to ventilate an identical test lung model. Raw calculations performed using the LTV-1200 underestimated the airway resistance calculated by conventional approaches under all test conditions. Raw calculations from the LTV-1200 should not be used interchangeably with those measured from the DXL for purposes of protocol driven decision making.