A partially collapsed lung happens when part of the lung deflates, either because air sacs lose their ability to stay open or because air leaks into the space surrounding the lung. The two main conditions behind it are atelectasis (where airways get blocked or compressed, causing lung tissue to deflate inward) and pneumothorax (where air escapes into the space between the lung and chest wall, pressing the lung inward from the outside). The causes range from something as routine as general anesthesia to something as sudden as a ruptured air blister on the lung’s surface.
Blocked Airways: Obstructive Causes
The most straightforward cause of a partially collapsed lung is a physical blockage inside an airway. When air can’t flow past the obstruction, the lung tissue beyond it gradually absorbs its remaining air and deflates. Three common culprits stand out.
Mucus plugs are buildups of thick phlegm that block airways, particularly after surgery when coughing is painful and breathing is shallow. They’re the single most common cause of atelectasis in hospitalized patients. Foreign objects cause partial collapse most often in young children who inhale small items like peanuts or toy parts. Tumors growing inside or pressing against an airway can narrow or seal it off entirely, trapping air on the other side until the tissue collapses.
Compression and Fluid Buildup
A lung can also collapse without any blockage in the airways. Outside pressure is enough. When fluid collects between the lung and the chest wall (a pleural effusion), or when a large mass pushes against the lung from outside, it forces air out of the tiny air sacs and compresses them flat. This is compression atelectasis, and it can happen alongside conditions like heart failure, pneumonia, or cancer that produces fluid around the lungs.
A related mechanism involves the loss of contact between the two thin membranes that line the chest cavity and the lung surface. Normally these membranes slide against each other and help keep the lung expanded. When fluid or air separates them, the lung loses the mechanical support holding it open and partially deflates on its own.
Surfactant Loss
Your lungs produce a slippery substance that coats the inside of each air sac and keeps it from collapsing in on itself, much like how soap in a bubble keeps the bubble from popping. When this substance breaks down or isn’t produced in sufficient quantities, smaller air sacs empty their air into larger ones and collapse. This is a key factor in acute respiratory distress syndrome and in premature infants whose lungs haven’t matured enough to produce adequate amounts.
Scarring and Tissue Damage
Severe lung infections or chronic inflammatory diseases can leave behind scar tissue that permanently shrinks part of the lung. As the scarring tightens, it pulls surrounding tissue inward and reduces the volume of that section. Conditions like tuberculosis and necrotizing pneumonia are common causes. In rare cases, a tumor can fill an entire lobe of the lung, replacing normal air sacs with dense tissue and causing that lobe to lose volume.
General Anesthesia: A Surprisingly Common Trigger
Even routine surgery under general anesthesia causes partial lung collapse in most patients. Roughly 10 to 15 percent of lung tissue collapses during an uneventful procedure. Several forces combine to make this happen.
When you’re lying flat and unconscious, your abdominal organs push your diaphragm upward, reducing the air your lungs can hold by nearly a liter compared to sitting upright. Paralytic drugs used during surgery shut down the muscles between your ribs, further shrinking lung capacity. On top of that, breathing pure oxygen (standard during anesthesia) accelerates collapse: oxygen absorbs into the blood faster than regular air, so if an airway gets even slightly blocked, the trapped oxygen disappears quickly and the tissue behind it deflates.
Post-surgical atelectasis is usually mild and resolves on its own as you wake up and start breathing deeply again. But in patients who are weak, in pain, or have underlying lung disease, it can persist and lead to low oxygen levels or infection.
Spontaneous Pneumothorax in Healthy People
Sometimes a partially collapsed lung strikes without any injury or illness. Primary spontaneous pneumothorax occurs when small air-filled blisters called blebs, which form on the surface of the lung, rupture and release air into the space around the lung. That escaped air presses against the lung from the outside, causing it to partially deflate.
Blebs can sit on the lung surface for years without causing problems. They’re invisible without imaging and produce no symptoms. A sudden change in air pressure, a sharp deep breath, or sometimes nothing identifiable at all can cause one to pop. A person can have anywhere from a single bleb to more than thirty.
This type of collapse disproportionately affects tall, thin young men. Researchers believe that rapid chest growth during adolescent growth spurts stretches lung tissue in ways that make blebs more likely to form. Smoking also significantly increases the risk, even in young people.
Traumatic Causes
Blunt force to the chest (car accidents, falls, contact sports) or penetrating injuries (stab wounds, broken ribs puncturing the lung) can allow air to leak into the pleural space and cause a partial collapse. Medical procedures can also trigger it. Inserting a central line into a vein near the collarbone, performing a lung biopsy, or even aggressive mechanical ventilation can accidentally puncture the lung surface.
How a Partial Collapse Is Detected
A chest X-ray is the first-line tool. Doctors look for direct signs like a visible white area where the collapsed tissue has become dense, or a shifted boundary between lung lobes. Indirect signs include the windpipe or heart shifting toward the collapsed side, the diaphragm sitting higher on that side, or the ribs appearing closer together. CT scans pick up smaller areas of collapse that X-rays miss and help distinguish between different causes.
How It’s Treated
Treatment depends entirely on the cause and severity. Small areas of collapse, especially after surgery, often resolve with deep breathing exercises using a handheld device called an incentive spirometer. You breathe in slowly through the device, which gives you visual feedback on how deeply you’re inhaling, then cough to clear loosened mucus. Positioning yourself so your head is lower than your chest can help drain secretions from affected areas.
For stubborn mucus plugs, doctors may use chest physiotherapy: rhythmic tapping on the chest wall over the collapsed area to shake mucus loose, sometimes combined with a vibrating vest or handheld vibration device. If that doesn’t work, a bronchoscopy lets a doctor thread a thin, flexible tube into the airway to suction out the blockage directly or, if a tumor is responsible, to remove or shrink it.
Patients who are too weak to cough effectively or who have dangerously low oxygen levels may be placed on continuous positive airway pressure (CPAP), which delivers a steady stream of pressurized air to help keep air sacs open. For pneumothorax, treatment ranges from observation for very small leaks to inserting a tube between the ribs to drain the trapped air and let the lung re-expand.