The Science Journal of the American Association for Respiratory Care

Original Contributions

August 2002 / Volume 47 / Number 8 / Page 887

Maintaining Oxygenation via Demand Oxygen Delivery During Rest and Exercise

Brian L Tiep MD, James Barnett RRT, George Schiffman MD, Oscar Sanchez, Rick Carter PhD MBA

BACKGROUND: Oxygen-conserving devices have been the foundation of highly portable oxygen systems that enable hypoxemic chronic lung disease patients to live active lives. Pulsing demand oxygen delivery systems (DODS) can adequately oxygenate most patients at rest and usually during exercise. However, some patients desaturate during exercise at DODS settings equivalent to continuous-flow oxygen. OBJECTIVE: Determine if design enhancements of the Oxymatic 401 DODS (including increased sensitivity, earlier inspiratory delivery, larger pulse volume, modified pulse contour, and higher settings) better maintain blood oxygen saturation (measured via pulse oximetry [SPO2]) in patients who severely desaturate during exercise. METHODS: We compared patients receiving DODS oxygen and patients receiving continuous-flow oxygen, during both rest and iso-exercise. SETTING: This study was conducted in the Pulmonary Rehabilitation Program at Mission Hospital, Regional Medical Center, Mission Viejo, California. SUBJECTS: We studied 10 patients with chronic lung disease and difficulty maintaining exercise SPO2 with DODS. Nine patients had chronic obstructive pulmonary disease and one had restrictive lung disease. The group's (mean ± SD) demographic and physiologic values included: age 67 ± 7 y, forced expiratory volume in the first second 0.79 ± 0.3 L, forced vital capacity 1.7 ± 0.7 L, and SPO2 88%. INTERVENTIONS: Resting SPO2 was measured during continuous oxygen flow and during DODS, at identical settings. SPO2 was allowed to stabilize at each level before recording. During treadmill exercise at identical work loads we measured continuous flow and DODS SPO2 at the same settings. If the DODS SPO2 was less than during the equivalent continuous flow, the DODS setting was increased for another treadmill trial. RESULTS: At rest the DODS was equivalent to continuous flow: SPO2 was 93.7 ± 2.1% with DODS and 93.8 ± 1.9% with continuous flow. During exercise at corresponding settings DODS SPO2 was 90.5 ± 3.8% and continuous-flow SPO2 was 93.1 ± 3.1%. Six subjects had SPO2 > 90%, with 4 of them achieving equivalency. At higher DODS settings SPO2 became equivalent: 92.5 ± 2.8%. The DODS oxygen-use efficiency advantage was 6.7-fold at rest and 5.6-fold during exercise, except with subjects who required a higher exercise DODS setting, with whom the DODS advantage was 4.3-fold. CONCLUSIONS: The redesigned Oxymatic 401 DODS maintains adequate SPO2 during rest and exercise, but some patients require the higher delivery settings. We recommend that all patients prescribed DODS undergo exercise evaluation with the prescribed DODS to ensure efficacy and determine the DODS settings required to maintain SPO2 at the prescribed limits.
Key words: oxygen delivery, oxygen conservation, exercise, treadmill, oxygen saturation.
[Respir Care 2002;47(8):887–892]

Introduction

The primary goals of medical care for patients with chronic lung disease are to manage the disease, improve physical and psychological function, and enhance quality of life. Oxygen therapy for patients with chronic obstructive pulmonary disease and hypoxemia is directed toward maintaining oxygen saturation at rest and preventing desaturation during exercise and sleep. Several portable oxygen systems have been designed to provide adequate oxygenation while minimizing the size and weight of the oxygen system. Further benefit is achieved through the use of portable systems that promote ambulation away from the home.

See The Related Editorial on Page 879

Portable oxygen supports chronic lung disease patients' ability to maintain an active lifestyle and participate in many of life's pleasures, thus improving quality of life. Oxygen conservation technology is among the most important developments in portable oxygen therapy in recent years. As the efficiency of oxygen delivery devices improve, these devices become smaller and more portable, thereby reducing the burden on the patient, from both an economic and physical perspective. A variety of oxygen-conserving devices, including reservoir cannulas, transtracheal catheters, and demand oxygen delivery systems (DODS), have provided the hypoxemic patient with choices and tradeoffs. The most efficient of these systems is the DODS, which delivers oxygen early in the inhalation phase, ensuring that a bolus of oxygen reaches the alveoli and avoiding the waste of oxygen that occurs with systems that deliver oxygen throughout inhalation and exhalation. DODS oxygen-use efficiency ranges from 2-fold to 7-fold better than continuous-flow oxygen delivery. That is, DODS can achieve the same oxygen saturation levels as continuous flow while using only one half to one seventh the oxygen.

Previous studies found DODS effective during rest, sleep, and exercise. Recently, however, it became apparent that some DODS users desaturate during exercise at DODS settings that correspond to continuous flow. In other words, DODS settings equivalent to continuous flow were insufficient to achieve equivalent oxygen saturation. That difference in equivalency between rest and exercise appears to result from several physiologic and mechanical factors. In an attempt to improve on several of those factors and fully meet the oxygenation needs of patients who do not adequately saturate with existing DODS during exercise, one of the DODS models, the Oxymatic 401 (CHAD Therapeutics, Chatsworth, California), was redesigned. Specifically, the pulse volume and sensitivity to inspiratory flow were increased, the delivery waveform was modified, and higher flow settings were added, all while retaining the DODS oxygen-use efficiency advantage.

The present study was designed to investigate if those design modifications achieve adequate oxygenation in DODS patients who desaturate during exercise.

The entire text of this article is available in the printed version of the August 2002 RESPIRATORY CARE.

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