OXYGEN THERAPY IN CHRONIC RESPIRATORY FAILURE (AMBULATORY AND HOME USE
Supplemental oxygen was the first treatment shown to improve survival in patients with chronic obstructive pulmonary disease (COPD). A multicenter clinical trial published in 1980 demonstrated the benefit of oxygen used continuously compared with oxygen only administered nocturnally. The current recommendations for oxygen therapy in patients with COPD are (1) partial pressure of oxygen in arterial blood (Pao2) of 55 mm Hg or below (or pulse oxygen saturation [Spo2] ≤88%) or (2) Pao2 of 56 to 60 mm Hg (Spo2, 89%) with erythrocytosis (hematocrit >56 mL/dL) or cor pulmonale. Because of the benefits of oxygen, reimbursement is available from most medical insurance payers. The long-term benefit of oxygen in patients with less severe hypoxemia is unknown.
Three types of oxygen systems are available: (1) gaseous
oxygen stored under high pressure in lighter weight aluminum or steel
cylinders, (2) oxygen stored in liquid form, and (3) concentrators that
are electrically powered and concentrate the oxygen in ambient air. To use
oxygen 24 hours a day, patients need systems that will provide oxygen in the
home and where they work during the day, at night, and during ambulation when
out of the house during the day. Oxygen systems can reliably and conveniently
provide oxygen in all of these circumstances. Smaller, lightweight oxygen
systems are more appropriate for use during ambulation, and it has been
recommended that systems designed for use during ambulation should weigh 5 lb
or less. Each patient should be evaluated individually and provided with an
oxygen system that best fills his or her needs. When prescribing oxygen, health
care providers should order the flow rate of oxygen needed to ensure an Spo2
of about 90%-92% at rest, during ambulation, and nocturnally. Home care oxygen
suppliers, health care providers, and patients should carefully consider which
oxygen system is best for each individual. The optimal oxygen system for each
patient is the one that best fulfills that person’s medical needs and allows him
or her to pursue an independent and functional lifestyle with careful
consideration of the oxygen flow rate and amount of time spent in various
activities inside and outside the home.
Oxygen concentrators were originally designed for use
in the home and are still widely used in that setting because of their
reliability, durability, and low maintenance requirements. Newer units are
smaller and quieter and can provide higher flow rates than previous models.
Battery-powered concentrators can be used for mobility and are allowed for use
on many commercial airliners.
Gaseous oxygen cylinders are available in a wide
variety of sizes. Small cylinders are convenient and light enough for patients to
carry over their shoulder. Larger cylinders contain more oxygen and provide a
longer duration of use, but they are heavier and thus more difficult for
patients to carry. Traditionally, gaseous cylinders had to be delivered to
patients by a home care oxygen company. However, some oxygen systems now
provide oxygen via concentrator while also filling a gaseous oxygen tank.
Liquid oxygen can be provided in a large tank for use
during the day. Smaller liquid tanks weighing 5 lb or less can be filled by
patients from the larger reservoir. One disadvantage of liquid oxygen is the need for
delivery on a regular basis.
To reduce the amount of oxygen used by patients,
oxygen conservers are commonly used in the home. These devices take advantage
of the fact that oxygen is only needed during inspiration and is wasted during
expiration. Moreover, only oxygen delivered during the early portion of
inspiration reaches gas-exchanging alveoli.
Oxygen is most often delivered to the nares by an
oxygen cannula. To be less obtrusive, the cannula can be embedded into eyeglass
frames. Oxygen can also be delivered transtracheally (i.e., through a catheter
placed through the neck into the trachea). Advantages of transtracheal oxygen
include a reduction in the flow rates needed compared with a nasal cannula,
elimination of nasal adverse effects, and the ability to conceal the catheter.
