The Science Journal of the American Association for Respiratory Care

2002 OPEN FORUM Abstracts

FACTORS AFFECTING OXYGEN DELIVERY BY BIPAP.

Andrew R. Schwartz, RRT, CPFT; Robert M. Kacmarek, PhD, RRT, FAARC; Dean R. Hess, PhD, RRT, FAARC. Massachusetts General Hospital and Harvard Medical School, Boston, MA.

Background: Oxygen administration is usually required for patients with acute respiratory failure requiring noninvasive ventilation. For the BiPAP ventilator, this is accomplished by O2 titration into the mask or ventilator circuit. We have anecdotally noted that arterial oxygen saturation varies with the leak port and BiPAP settings.

Hypothesis: Oxygen delivery during BiPAP is affected by the leak port and BiPAP settings.

Methods: A Puritan-Bennett 7200 ventilator (Tyco, Carlsbad, CA) was attached to one chamber of a dual-chambered test lung (Michigan Instruments, Grand Rapids, MI). A lift bar was placed between the chambers such that the ventilator triggered simulated spontaneous breathing of the second chamber. The second chamber was connected to the head of a manikin. A Mirage oronasal face mask (Resmed, Poway, CA) was attached to the manikin. A single limb circuit was attached between the mask and a Synchrony BiPAP ventilator (Respironics, Pittsburgh, PA). Three leak ports were compared: leak in the Mirage mask, Respironics Plateau Exhalation Valve (PEV) with Mirage mask leak port occluded, and Respironics Disposable circuit with Exhalation Port (EP) and Mirage mask leak port occluded. BiPAP settings of 10/5, 15/5, 20/5, 15/10/ 20/10, and 25/10 cm H2O were used at respiratory rates of 15 and 25/min. O2 was titrated into the mask or into the circuit at the ventilator outlet using flows of 5 and 10 L/min. CO2 was titrated into the lung model to produce an end-tidal PCO2 of 40 or 75 mm Hg. O2 concentration was measured between the manikin head and the test lung (PB 7820 oxygen monitor).

Results: The O2 concentration was greater when O2 was titrated into the circuit with the leak port in the mask, whereas O2 concentration was greater when O2 was titrated into the mask for the PEV and EP (see Table). O2 concentration was lower with the leak port in the mask (P<0.001), a higher IPAP (P<0.001), and a higher EPAP (P<0.001). Delivered O2 concentration was not affected by respiratory rate (P=0.22) or exhaled PCO2 (P=0.74).

Effect of Leak Port and O2 Titration Site on Delivered O2 Concentration
  Mask PEV EP
O2 into mask      
5 L/min 22±1% 36±6% 39±8%
10 L/min 26±2% 52±11% 58±14%
O2 into circuit      
5 L/min 31±3% 35±2% 37±4%
10 L/min 40±5% 48±4% 50±6

Conclusions: Delivered O2 concentration during BiPAP is a complex interaction between the site of the leak port, the site of O2 titration, the settings on the BiPAP ventilator, and the O2 flow. Because of this, it is important to continuously estimate arterial oxygen saturation using pulse oximetry when patients with acute respiratory failure are receiving noninvasive ventilation using a BiPAP ventilator.

OF-02-082

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