Utilization of the Volume Diffusive Respirator in Upper Airway Obstruction and Acute Lung Injury
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Utilization of the Volume Diffusive Respirator in Upper Airway Obstruction and Acute Lung Injury
Providing adequate gas exchange in patients exhibiting upper airway obstruction or acute lung injury remains a clinical challenge. The goal of improving both ventilation and oxygenation without causing ventilator-induced trauma can be difficult to attain.
Introduced recently to Lehigh Valley Hospital Center by Dr. William Dougherty, the Volume Diffusive Respirator (VDR) has made a tremendous difference in patient care. Currently Lehigh’s burn unit medical director, Dougherty had previously used the VDR in his medical practice and successfully met physiological end points without negative impact to his patients.
Dr. Forest Bird’s brainchild, the VDR was introduced in the U.S. in the late 1980s, and has been utilized at clinical sites. The VDR is classified as a pneumatically powered, time-cycled, pressure limited ventilator and incorporates a high-flow interrupter. Delivering high frequency volumes between 200-900 times per minute, the percussive nature of the oscillations facilitates gas diffusion and internal percussion enhances mucokinesis.
The VDR’s unique Phasitron is a sliding venturi acting as both an inhalation and exhalation valve with a mechanical /physiological interface. Oscillatory breaths are precisely stacked to a selected inspiratory pressure with an equilibrium established enhancing diffusion and mixing of gases. Compared to jet ventilators, the VDR provides for a convective component independent of any special jet cannula or endotracheal tube. Unlike high-frequency oscillatory ventilation, exhalation is passive.
Ventilator adjustments to correct arterial blood gas derangements require a solid knowledge of pressure limited ventilation and high frequency ventilation, which is also true of the VDR. Initial ventilator settings include: convective or phase rate, I:E ratio, peak inspiratory pressure, demand and oscillatory PEEP, oscillatory rate, and FIO2. The pulsatile flow rate setting, oscillatory frequency, and gas entrainment are the variables determining patient tidal volume.
Peak inspiratory pressure and mean airway pressure are both measured at the proximal airway. But exhaled gas cannot be measured, and utilizing a continuous ETCO2 monitor determines the level of ventilation and airway obstruction. Airway obstruction is minimized, however, with a high output aerosol generator providing patient airway humidification.
Since early August, the VDR has ventilated 11 patients including patients with significant upper airway obstruction secondary to thermal injury who have failed conventional lung ventilation strategies, including a patient who received a thermal burn and a patient with a closed head injury.
Ventilator management of patients with upper airway obstruction or acute lung injury can be often complex and problematic. The VDR has proven useful, and is another weapon in the war against respiratory insufficiency.
Ken Miller is a staff therapist at Lehigh Valley Medical center, Allentown, Pa.
