Chronic Obstructive Pulmonary Disease (COPD) is a progressive lung condition characterized by restricted airflow, making breathing increasingly difficult over time. As COPD advances, the lungs struggle to transfer sufficient oxygen into the bloodstream, leading to hypoxemia, or low blood oxygen. When a patient’s oxygen levels fall below a certain threshold, supplemental oxygen therapy (SOT) becomes a necessary treatment. This therapy ensures the body’s organs receive the oxygen they require.
Medical Criteria for Long-Term Oxygen Therapy
Qualification for Long-Term Oxygen Therapy (LTOT) is based on specific, measurable levels of oxygen in the blood, determined when a patient is clinically stable. The primary criterion for LTOT prescription is a resting partial pressure of oxygen in arterial blood (PaO2) of 55 millimeters of mercury (mm Hg) or lower. This measurement is equivalent to an oxygen saturation level (SpO2) of 88% or less, measured while the patient is breathing room air. These low levels must be confirmed on at least two separate occasions to ensure the hypoxemia is persistent.
A patient may also qualify for LTOT with a resting PaO2 between 56 and 59 mm Hg, or an SpO2 of 89%, if they exhibit signs of related complications. These complications include peripheral edema suggesting right-sided heart failure (Cor Pulmonale). Other qualifying conditions at this intermediate level include evidence of pulmonary hypertension or polycythemia, indicated by a hematocrit greater than 55%. Continuous LTOT is defined as using supplemental oxygen for a minimum of 15 hours per day to achieve a proven survival benefit.
Diagnostic Testing Procedures to Confirm Hypoxemia
Determining a patient’s oxygen status involves two primary diagnostic tools: Arterial Blood Gas (ABG) analysis and pulse oximetry. The ABG test is considered the gold standard. It involves drawing a blood sample from an artery to directly measure the partial pressure of oxygen (PaO2) and carbon dioxide. This invasive test also provides the blood’s pH level, which is necessary to evaluate the body’s acid-base status and ventilation efficiency.
Pulse oximetry, or SpO2 measurement, is a non-invasive method that uses a sensor to estimate the percentage of hemoglobin carrying oxygen. While less precise than an ABG, oximetry is easy to use and provides continuous monitoring of oxygen saturation. For qualification purposes, all testing must be performed when the patient is in a stable clinical state, meaning they are not experiencing an acute COPD exacerbation.
Beyond resting measurements, oxygen needs during physical activity are assessed using a 6-minute walk test (6MWT). During this procedure, the patient walks while a pulse oximeter monitors their saturation levels. If the patient’s SpO2 drops below 90% or falls significantly from their baseline reading, supplemental oxygen may be prescribed for use during exertion, known as ambulatory oxygen. Nocturnal oximetry records oxygen levels continuously overnight to detect desaturation during sleep, which can occur even if daytime levels are normal.
Understanding Oxygen Delivery Systems and Usage Schedules
Once supplemental oxygen is prescribed, the patient receives one of three main types of delivery systems for home use:
- Oxygen Concentrators: These electrical devices filter nitrogen from the air to deliver concentrated oxygen flow. Stationary concentrators provide continuous supply at home, while Portable Oxygen Concentrators (POCs) are battery-operated units that increase mobility.
- Compressed Gas: Oxygen is stored as a gas in metal tanks of various sizes. These tanks are simple to use and are often kept as a backup, but they contain a finite supply and require regular deliveries to be refilled.
- Liquid Oxygen Systems: These systems store oxygen as a super-cooled liquid, offering high capacity in a small volume. This provides excellent portability for those needing higher flow rates, though the liquid evaporates over time.
Oxygen is prescribed according to specific schedules tailored to the patient’s needs. Continuous usage is the most common prescription for LTOT. Some patients only require nocturnal oxygen, used during sleep to combat desaturation that occurs naturally overnight. Intermittent, or ambulatory, usage is reserved for patients who require supplemental oxygen only when performing physical activities like walking or exercise.
Health Consequences of Untreated Low Oxygen Levels
Ignoring the need for prescribed oxygen therapy exposes the body to chronic hypoxemia, which can lead to long-term health complications. The heart and lungs are especially vulnerable to the effects of persistently low oxygen levels. One consequence is the development or worsening of pulmonary hypertension, where the arteries in the lungs constrict in response to low oxygen, raising pressure in the pulmonary circulation.
This increased pressure forces the right side of the heart to work harder to pump blood through the lungs, eventually leading to right-sided heart failure (Cor Pulmonale). Chronic hypoxemia also stimulates the excessive production of red blood cells, resulting in secondary polycythemia. This condition thickens the blood, increasing the risk of blood clots and strokes.
Untreated oxygen deprivation contributes to systemic inflammation and skeletal muscle dysfunction, leading to diminished physical endurance and a lower overall quality of life. Chronic hypoxemia significantly increases the risk of hospitalization and death. Consistent use of supplemental oxygen is the only proven therapy to slow the progression of these consequences and improve long-term survival in patients with severe COPD.