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Guide to Prescribing Home Oxygen
by Thomas L. Petty, M.D.
Contents
The Key to Prescibing Home Oxygen
Introduction
Patient Considerations in Selecting Equipment
INTRODUCTION
The purpose of this guide is to direct the physician and other healthcare providers in deciding which oxygen modality is best for each long-term oxygen therapy (LTOT) patient. This document provides information on how to match the appropriate piece of oxygen equipment to the right patient.
COPD Disease State
Chronic hypoxemia results in reactive pulmonary hypertension, which increases right ventricular afterload. This results in limitation of cardiac output of the right ventricle and eventual cor pulmonale and right heart failure. An expanded red cell mass and increased plasma volume due to salt and water retention by the kidneys in response to hypoxemia add to the hemodynamic burden. However, pulmonary pressures are only modestly elevated in COPD and in most interstitial lung diseases. The levels of pulmonary hypertension in COPD are considerably less severe than the pulmonary pressures associated with primary and thromboembolic forms of pulmonary hypertension. Why cor pulmonale in COPD carries such a poor prognosis is somewhat difficult to comprehend. The answer may lie in the fact that the consequences of chronic hypoxemia are not just cardiovascular, hematologic and renal in origin. Thus, the presence of cor pulmonale in COPD may simply be a surrogate marker of disease severity. The multiorgan deterioration in advanced COPD and other chronic pulmonary problems appears to be global and likely is an interaction between hypoxemia and nutritional-metabolic abnormalities. Subtle, but progressive multiorgan dysfunction occurs in advanced stages of COPD and related disorders such as interstitial fibrosis and cystic fibrosis, which are also characterized by chronic progressive hypoxemia. In any case, correction of hypoxemia results in improved hemodynamics, reduction of red cell mass, dry weight gain and improved exercise tolerance.' Improved brain function and quality of life accompany these physiologic improvements in response to LTOT.2
Indications for LTOT
Table 1 lists the commonly accepted indications for LTOT and the requirements for oxygen prescription from the Health Care Finance Administration (HCFA) and certain insurance plans. When daytime normoxia is present, but sleep-related hypoxemia has been established by continuous nocturnal monitoring of oxygen saturation, oxygen can be prescribed during the hours of sleep when there is clinical evidence of harm from the consequences of hypoxemia, i.e., morning headaches, clinical evidence of pulmonary hypertension and erythrocytosis. Similarly, if exercise-related hypoxemia is demonstrated by pulse oximetry, ambulatory oxygen can be prescribed and is particularly appropriate if it can be demonstrated those improved exercise-tolerance results are from ambulatory oxygen therapy
| Patient Selection Criteria |
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| Oxygen Dose |
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| Expected Outcomes |
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Controlled Clinical Trials of LTOT
Two major randomized controlled clinical trials conducted in the late 1970's firmly established the scientific basis for LTOT. The Nocturnal Oxygen Therapy Trial (NOTT) studied what was intended to be continuous oxygen therapy (COT), using an ambulatory system which was most often liquid portable oxygen compared with nocturnal oxygen therapy (NOT) for 12 hours per day which most commonly employed a concentrator. In a few patients, high pressure oxygen tanks were used for NOT.3 This study was conducted in six North American cities (n=203). The general conclusion that can be made from this study is that patients who used continuous Oz therapy had more benefits than those who used intermittent Oi therapy.
The second study was the British Medical Research Council (MRC) controlled clinical trials conducted in the United Kingdom. This study compared 15 hours of oxygen from a stationary source with no oxygen in a random assignment of patients with severe COPD and chronic stable hypoxemia. Since the severity of disease and the demographics of the NOTT and MRC studies were similar, it is reasonable to compare the outcomes of the four study groups. The survival data are presented in Figure I.5 These data indicate that the survival in advanced COPD with chronic stable hypoxemia was poor with no supplemental oxygen. It was better to a statistically significant degree with oxygen delivered approximately 12 hours per day in the NOTT trial or 15 hours per day in the British MRC Clinical Trial. Survival was much better with more continuous oxygen therapy (COT). However, in the NOTT, review of diaries used in COT patients showed that the median duration of oxygen actually delivered was 19.4 hours per day and the average use was 17.7 hours per day. (See Figure 1.)
The improved survival in the LTOT patients compared with the other groups could have resulted from the longer duration of oxygen administration. It is a reasonable hypothesis that ability to ambulate and participate in more activities of daily living while using ambulatory oxygen resulted in improved physical conditioning and psychosocial adjustments that contributed to the improved survival and quality of life.