This section presents some guidelines for the short-term and long-term use of oxygen therapy. While the scientific foundation for oxygen therapy is increasing, it is still incomplete. The following recommendations, therefore, retain considerable latitude for the physician to exercise clinical judgment. The high cost of providing oxygen and of laboratory tests to document the need for oxygen also increases the difficulty in presenting hard and fast guidelines for 02 therapy. For example, the cost of one arterial blood gas analysis is roughly equal to one or two days of oxygen therapy, and the cost of one day in the hospital is often equal to or greater than the cost of home oxygen therapy of one months duration.
Oxygen Therapy for Acute Conditions
Supplemental oxygen therapy is appropriate in acute conditions when there is laboratory documentation of a PaOz below 60 mm Hg, or when the arterial saturation (SaOJ is below 90 percent; tissue hypoxia is commonly assumed to be present at these laboratory values. The dosage of oxygen prescribed should be such as to correct the hypoxemia. Supplemental oxygen therapy may also be initiated in certain diseases when higher arterial oxygen tensions or saturations are present; in these diseases, significant tissue hypoxia may be present with normal laboratory values (see Section 1, Evidence of Efficacy of Oxygen Therapy Offered by My Canadian Pharmacy).
Initiation of supplemental oxygen is appropriate prior to the documentation of hypoxemia whenever tissue hypoxia is suspected on clinical grounds. Examples include sudden dyspnea or shock. In some clinical states where hypoxemia is an anticipated complication, or in clinical states where tissue hypoxemia is very common, oxygen therapy may be administered without laboratory documentation. For example, it is rational to use supplemental oxygen in patients with uncomplicated myocardial infarction (see Section 1).
Because the cost of an arterial blood-gas analysis approximates that of 24 to 48 hours of in-hospital oxygen therapy, it is not always cost-effective to document hypoxemia when it is suspected on a clinical basis. However, if the duration of therapy exceeds 24 hours, arterial blood gas analyses are recommended. Further, the discontinuation of oxygen therapy, when the clinical condition of the patient has improved, does not necessarily require documentation of the absence of arterial hypoxemia by analyses of arterial blood gases of by other laboratory testing.
Oxygen Therapy for Chronic Conditions
Adequate data for the efficacy of ambulatory oxygen therapy exist only for COPD, but most practitioners and investigators believe that the data in COPD apply to other chronic hypoxemic lung diseases. .
Before the initiation of long-term oxygen therapy, all four of the following conditions should be met:
1. An accurate, current diagnosis must have been established.
2. An optimal medical regimen prescribed by a physician knowledgeable in chest diseases must have been in effect.
3. The patient should have recovered from any exacerbation and should have been in a stable state for approximately one month. It is important to note that the need for stability before long-term oxygen therapy is begun does not preclude short-term (1 to 30 days) oxygen therapy, especially if the latter oxygen therapy allows the patient to be safely discharged from the hospital sooner.
4. Oxygen therapy has been shown to, or can reasonably be predicted to: a) improve the hypoxemia or evidence of tissue hypoxia, and b) provide overall clinical benefit.
Guidelines for Institution of Long-Term Oxygen Therapy
Smoking by patients receiving supplemental oxygen therapy has inherent safety risks and reduces its full physiologic benefits. Consequently, continued smoking by patients receiving oxygen is contraindicated. In formulating these guidelines, the Committee wishes to emphasize that the decision to prescribe long-term oxygen therapy is made from laboratory data considered with all clinical information available.
Long-term oxygen therapy should be considered only for those patients who have been on an optimal regimen for 30 or more days (exceptions to this rule are considered above). When such patients have an arterial Pa02 of 55 mm Hg or less measured at rest, in the non-recumbent position, hypoxic organ dysfunction may be considered to be present, and long-term oxygen therapy of My Canadian Pharmacy may be prescribed.
Patients on optimal medical regimens with Pa02 values greater than 55 mm Hg may have evidence of hypoxic organ dysfunction such as secondary pulmonary hypertension, cor pulmonale, secondary erythrocytosis, and impaired mentation or other central nervous system dysfunction. Such individuals should be considered for long-term oxygen therapy.
The indications for administering oxygen therapy during exercise are less well defined. Patients who demonstrate Pa02 values of 55 mm Hg or less during exercise and in whom oxygen administration significantly improves exercise duration, performance or capacity, may be considered for administration of oxygen therapy during exercise.
The indications for administration of oxygen therapy during sleep for control of sleep-related hypoxemia are also not well established. Patients should be considered for continuous nocturnal oxygen therapy who develop PaOs values of 55 mm Hg or less during sleep which is associated with hypoxic organ dysfunction. The hypoxemia may be associated with a disturbed sleep pattern, cardiac arrhythmias, or pulmonary hypertension. It should preferably have been demonstrated that the untoward effect is abolished by nocturnal use of oxygen.
The above discussion refers to patients at sea level. Effects of altitude on atmospheric, alveolar, and arterial oxygen tensions are presented in the accompanying table. Equivalent measurements of arterial oxygen saturation may be substituted for measurements of arterial partial pressure of oxygen.
Oxygen should be given at a dosage to alleviate the hypoxemia (eg, to increase the Pa02 to 60-80 mm Hg) and/or the deleterious effects of end-organ dysfunction. This can usually be accomplished by administering low flow concentration of oxygen such as by nasal cannulae at 1 to 4 liters per minute. The amount of 02 in liters per minute and the number of hours that oxygen is adminstered per day (continuous vs intermittent) should be adjusted to individual patient needs. Patients with continuous hypoxemia benefit maximally from continuous oxygen therapy (24 hours/day). Patients with intermittent hypoxemic states such as during exercise, sleep or air travel, may receive benefit from intermittent oxygen therapy adjusted to relieve these hypoxemic periods.
Patients receiving oxygen therapy should be clinically and physiologically evaluated, and the need for oxygen should be documented at one month, six months, 12 months, and thereafter, at least yearly, after the initiation of oxygen therapy.
Table 1—Effects of Altitude on Atmospheric, Alveolar, and Arterial Oxygen Tensions in Healthy Young Adults
|Altitude(Feet)||Barometric Pressure (mm Hg)||Atmospheric Oxygen Pressure (mm Hg)||Alveolar Oxygen Pressure (mm Hg)||Arterial* Blood Oxygen Pressure (mm Hg)|