Supplemental oxygen therapy increases the amount of oxygen in the bloodstream when the lungs cannot adequately supply it. This therapy treats hypoxemia, the medical term for low blood oxygen levels. Because oxygen is considered a drug, it must be used under the direction and supervision of a healthcare provider and requires a formal prescription.
How Oxygen Saturation is Measured
Measuring the percentage of oxygen saturation (SpO2) in the blood determines the need for supplemental oxygen. This is most commonly done using a pulse oximeter, a small, non-invasive device clipped onto a finger or earlobe. The device works by emitting two different wavelengths of light, which pass through the tissue to a sensor. Oxygen-carrying and non-oxygen-carrying hemoglobin absorb these light wavelengths differently, allowing the oximeter to calculate the saturation percentage.
For most healthy individuals, normal oxygen saturation ranges between 95% and 100%. A reading below 90% is considered hypoxemia and requires medical attention. Healthcare providers typically prescribe supplemental oxygen when SpO2 levels persistently drop to 88% or 90% or below, especially during rest, sleep, or activity. The goal of therapy is to maintain a saturation level above 90%.
The most accurate measurement of blood oxygen levels is obtained through an Arterial Blood Gas (ABG) test. This invasive test involves drawing a blood sample from an artery to measure the partial pressure of oxygen (PaO2) dissolved in the blood. A PaO2 value below 60 millimeters of mercury (mm Hg) is considered hypoxemic and indicates the need for oxygen therapy. ABG testing is the gold standard for assessing respiratory function.
Common Causes of Low Oxygen Levels
Low oxygen levels occur when the body’s gas exchange process is disrupted, preventing sufficient oxygen from moving from the lungs into the bloodstream. This disruption often stems from a ventilation-perfusion (V/Q) mismatch, an imbalance between the air reaching the alveoli and the blood flow surrounding them. Another element is diffusion impairment, where damage to the lung tissue makes it harder for oxygen to pass into the blood.
Chronic Obstructive Pulmonary Disease (COPD), which includes emphysema and chronic bronchitis, is a primary cause of persistent hypoxemia. In emphysema, the air sacs are permanently damaged and lose elasticity, significantly reducing the surface area available for gas exchange. Interstitial Lung Diseases, such as pulmonary fibrosis, cause scarring and stiffness in the lung tissue, leading to diffusion impairment that slows the rate of oxygen uptake.
Acute medical events can also trigger a sudden need for supplemental oxygen. Severe pneumonia causes inflammation and fluid buildup in the alveoli, blocking oxygen transfer into the blood. A pulmonary embolism is an acute condition where a blood clot lodges in the lung’s arteries, creating a V/Q mismatch. Oxygen is also used in acute exacerbations of asthma, where bronchospasm severely limits the air reaching the gas-exchanging units.
Conditions involving temporary drops in oxygen saturation include obstructive sleep apnea, where repeated airway collapse causes brief periods of hypoxemia during sleep. Environmental factors can also induce hypoxemia in healthy individuals, as the lower atmospheric pressure at high altitudes reduces the concentration of oxygen available for absorption.
Delivery Systems for Supplemental Oxygen
Several systems are available to deliver supplemental oxygen, categorized by their source and the interface used by the patient. Oxygen concentrators are the most common stationary device for home use, operating electrically to filter nitrogen from ambient air and deliver purified oxygen. These units provide an uninterrupted supply, limited only by electricity.
For use outside the home, patients utilize compressed gas cylinders, which store oxygen under high pressure in metal tanks, or liquid oxygen systems. Portable oxygen concentrators (POCs) offer a battery-powered alternative that generates oxygen on demand, making them a popular choice for active individuals, including for air travel.
Oxygen is delivered through an interface, with the nasal cannula being the most common low-flow device, consisting of two small prongs that sit inside the nostrils. For patients requiring higher concentrations, simple face masks or non-rebreather masks are used, which cover both the nose and mouth. Delivery can be continuous flow, where oxygen flows steadily, or a pulse dose method, which delivers a burst of oxygen only when the patient inhales.
Home Use and Safety Considerations
Using supplemental oxygen at home requires strict adherence to safety protocols. Since oxygen is a prescribed medication, the flow rate, measured in liters per minute (LPM), should never be adjusted without explicit direction from a physician. For some patients with chronic respiratory failure, particularly those with COPD, receiving too much oxygen can suppress the drive to breathe, leading to dangerously high carbon dioxide levels.
The primary safety concern is the risk of fire, as oxygen intensely supports combustion. Users must maintain a distance of at least five to ten feet between the oxygen unit and any heat source or open flame, including gas stoves, candles, and electric heaters. Smoking or allowing others to smoke near the equipment is strictly prohibited, and “No Smoking” signs should be posted prominently.
Patients should also avoid using oil-based products like petroleum jelly, hand creams, or aerosol sprays near the oxygen, as these materials can ignite easily. Tanks must be secured upright to prevent them from falling, and concentrators should be placed in well-ventilated areas away from walls or curtains to ensure proper airflow.