Chronic respiratory failure is a condition where your lungs can no longer move enough oxygen into your blood, remove enough carbon dioxide, or both. Unlike acute respiratory failure, which strikes suddenly, the chronic form develops over weeks, months, or years as an underlying lung or neuromuscular disease slowly worsens. It’s defined by specific blood gas levels: an oxygen level (PaO2) below 60 mmHg or a carbon dioxide level (PaCO2) above 45 mmHg on an arterial blood gas test, persisting over time.
Two Types of Chronic Respiratory Failure
There are two forms, and the distinction matters because they have different causes and different treatment priorities.
Type 1 (hypoxemic): Your blood oxygen drops too low, but carbon dioxide levels stay roughly normal. This happens when parts of your lungs fill with fluid, collapse, or become scarred, so blood passes through without picking up oxygen. The oxygen level in that blood is only about 40 mmHg, and when it mixes with properly oxygenated blood, overall oxygen content drops significantly. Conditions like interstitial lung disease and advanced heart failure are common culprits.
Type 2 (hypercapnic): Both oxygen and carbon dioxide are affected. Your lungs can’t move enough air in and out, so carbon dioxide builds up while oxygen falls. This is the pattern seen in severe COPD, obesity-related breathing problems, and neuromuscular diseases that weaken the muscles responsible for breathing. Normal PaCO2 sits between 35 and 45 mmHg. In type 2 failure, it rises above 45 mmHg and stays there.
What Causes It
Chronic respiratory failure is almost always the end result of another long-standing condition. The most common cause is COPD, where mucus buildup and airway narrowing progressively reduce airflow over years. Interstitial lung diseases, which scar and stiffen the tissue between the air sacs, are another major cause. Cystic fibrosis, severe asthma, and bronchiectasis can also lead to it.
Not all causes originate in the lungs themselves. Neuromuscular diseases like ALS (amyotrophic lateral sclerosis), muscular dystrophy, myasthenia gravis, and Guillain-Barré syndrome weaken the diaphragm and chest wall muscles that power breathing. Spinal cord injuries can do the same. In these cases, the lungs may be structurally healthy, but the body simply can’t ventilate them properly, leading to carbon dioxide retention.
Severe obesity is an underrecognized cause. Excess weight around the chest and abdomen restricts lung expansion, gradually leading to chronically elevated carbon dioxide levels, a pattern sometimes called obesity hypoventilation syndrome.
How Gas Exchange Breaks Down
Healthy lungs match airflow and blood flow precisely across millions of tiny air sacs. Each one receives a constant stream of fresh air and a constant stream of blood, and gases diffuse across the thin membrane between them. Chronic respiratory failure disrupts this in several ways.
When air sacs collapse or fill with fluid or scar tissue, blood flows past them without exchanging gases. This is called shunting, and it directly lowers blood oxygen. When the walls of the air sacs thicken from inflammation or scarring, oxygen takes longer to cross into the bloodstream, and some blood passes through only partially oxygenated.
The reverse problem also occurs. When blood vessels in the lungs become blocked or destroyed (as in emphysema), air reaches parts of the lung that have no blood flow. That ventilation is wasted, creating “dead space” that reduces the body’s ability to clear carbon dioxide. Over time, the body compensates by breathing faster or harder, but eventually those compensatory mechanisms run out.
Symptoms and Warning Signs
Because chronic respiratory failure develops gradually, early symptoms are easy to dismiss. Shortness of breath during activity is usually the first sign, eventually progressing to breathlessness at rest. Many people develop a pattern of breathing through pursed lips, which instinctively helps keep airways open longer during exhalation.
Low oxygen levels cause a bluish tint to the lips, fingertips, or skin (cyanosis), along with fatigue, poor exercise tolerance, and morning headaches. When carbon dioxide builds up, it affects the brain: you may notice confusion, difficulty concentrating, daytime sleepiness, or personality changes. In more advanced cases, visible use of neck and shoulder muscles to breathe becomes apparent, and even holding a conversation can leave you winded.
Complications Over Time
Living with chronically low oxygen triggers a cascade of secondary problems. The body responds to persistent hypoxia by producing more red blood cells, a condition called secondary polycythemia. While this sounds like a helpful adaptation, the thicker blood actually increases the workload on the heart and raises the risk of clots.
The lungs’ blood vessels constrict in response to low oxygen, raising pressure in the pulmonary arteries. Over time, this forces the right side of the heart to pump harder, eventually leading to right-sided heart failure, known as cor pulmonale. Polycythemia accelerates this process. Together, pulmonary hypertension and cor pulmonale are among the most serious complications of chronic respiratory failure and are linked to significantly worse outcomes.
How It’s Diagnosed
The primary diagnostic tool is an arterial blood gas (ABG) test, a blood sample taken from an artery (usually at the wrist) that measures oxygen, carbon dioxide, and pH levels. Normal arterial oxygen sits between 75 and 100 mmHg, and normal pH is 7.35 to 7.45. In chronic respiratory failure, the pH is often closer to normal despite elevated carbon dioxide, because the kidneys gradually compensate by retaining bicarbonate. This is one way clinicians distinguish chronic failure from an acute episode, where pH drops sharply.
Pulmonary function tests, chest imaging, and overnight pulse oximetry (which tracks oxygen levels during sleep) help identify the underlying cause and severity. Sleep studies are particularly important for people whose oxygen drops mainly at night, a common pattern in neuromuscular diseases and obesity hypoventilation.
Long-Term Oxygen Therapy
Supplemental oxygen is the cornerstone treatment for chronic hypoxemic respiratory failure. You qualify for long-term oxygen therapy if your resting PaO2 is at or below 55 mmHg (roughly equivalent to a pulse oximeter reading in the mid-to-upper 80s). If your levels are slightly higher, between 56 and 59 mmHg, oxygen is still recommended when there are signs of complications like an elevated red blood cell count or cor pulmonale.
For people whose oxygen drops mainly during sleep, therapy is indicated when saturation falls below 90% for two hours or more overnight. In practice, this means many people use oxygen through a nasal cannula while sleeping and during physical activity, while some need it continuously. Landmark trials have shown that using oxygen for at least 15 hours a day improves survival in people with severe chronic hypoxemia.
Breathing Support at Home
When carbon dioxide levels remain elevated despite other treatments, noninvasive ventilation (NIV) becomes an important option. This involves a mask worn over the nose or face, connected to a machine that delivers pressurized air to assist each breath. It works by doing some of the mechanical work of breathing, allowing tired respiratory muscles to rest and helping flush out carbon dioxide.
For people with severe COPD and persistent carbon dioxide levels above 53 mmHg, long-term home NIV has been shown to improve lung function, reduce breathlessness, improve sleep quality, and lower hospital readmission rates. In one major trial, COPD patients who used NIV at home after a hospitalization for respiratory failure had significantly fewer readmissions over the following year. NIV is also a standard long-term treatment for neuromuscular diseases that affect breathing, where it can sustain quality of life for years.
What the Prognosis Looks Like
Prognosis depends heavily on the underlying disease, its severity, and how well it responds to treatment. The numbers are sobering for advanced COPD with respiratory failure: one large study found a 1-year mortality rate of about 44% among COPD patients hospitalized for acute-on-chronic respiratory failure requiring ventilatory support, rising to 56% at two years. A separate study reported 5-year mortality of 74% in a similar population. These figures reflect the most severe end of the spectrum, where patients have already been hospitalized for a crisis.
Earlier-stage chronic respiratory failure, managed with oxygen therapy and breathing support before repeated hospitalizations, carries a better outlook. The key modifiable factors are staying on prescribed oxygen therapy consistently, using NIV as directed, treating the underlying disease aggressively, maintaining physical activity through pulmonary rehabilitation, and avoiding respiratory infections through vaccination. Smoking cessation, for those with COPD, remains the single most impactful intervention at any stage.