Some degree of lung collapse after open heart surgery is not just common, it is closer to the rule than the exception. In a recent audit of over 6,000 cardiac surgery patients at a single center, atelectasis (the medical term for partial or complete lung collapse) was the single most frequent pulmonary complication, affecting roughly one in four patients before they left the hospital. The reasons are layered: the chest is opened wide, the lungs are deflated during bypass, nerves can be chilled by ice used to protect the heart, and post-surgical pain discourages the deep breathing needed to keep lung tissue inflated. Understanding what drives this complication and how it is managed helps explain why respiratory therapy starts so quickly after surgery and why most patients recover their lung function over weeks to months.
How Often It Happens
The numbers depend on how aggressively doctors look for the problem and how they define it. A tertiary-center audit covering 6,138 cardiac surgery patients found that about 32.5 percent developed some form of pulmonary complication before discharge, and atelectasis alone accounted for 23.7 percent of all patients, making it the most common lung problem by a wide margin. Respiratory failure (18.5 percent) and pleural effusion (10.5 percent) were the next most frequent issues.1Annals of Thoracic Surgery Short Reports. Pulmonary Complications After Cardiac Surgical Procedures: A Tertiary Centre Audit of Elective and Urgent Cases Other reviews place the overall rate of pulmonary complications after surgery involving cardiopulmonary bypass at 20 to 35 percent.2PubMed Central. Lung injury after cardiopulmonary bypass: Alternative treatment prospects
Most of this collapse is partial, not total. A complete collapse of an entire lung during or after open heart surgery is far less common and typically makes the news in a patient’s chart because it demands urgent attention. The everyday version is a more subtle loss of volume, often concentrated in the lower left lobe, that may show up on a routine post-operative chest X-ray without causing dramatic symptoms. Still, even partial collapse reduces oxygen exchange and can set the stage for pneumonia if it lingers, so surgical teams treat it seriously.
Why Open Heart Surgery Is Uniquely Hard on the Lungs
Several features of cardiac surgery converge to make lung collapse far more likely than it would be after, say, a hip replacement or even most abdominal operations.
The most direct factor is the use of cardiopulmonary bypass, the heart-lung machine. While the machine takes over circulation, the lungs are essentially parked: ventilation is stopped or drastically reduced, and the lung tissue sits partially deflated, sometimes for hours. During that idle period, the small air sacs begin to stick together and lose volume. On top of that, the bypass circuit triggers a body-wide inflammatory response. Blood passing through the machine’s tubing activates immune pathways that can damage the delicate lining of the lungs, compounding the collapse with swelling and fluid accumulation.2PubMed Central. Lung injury after cardiopulmonary bypass: Alternative treatment prospects
General anesthesia itself also contributes. Anesthetic drugs relax the diaphragm and chest wall muscles, allowing the weight of the heart and abdominal organs to compress the lower portions of the lungs. This compression-driven collapse begins within minutes of induction and can persist for days afterward. Patients who are obese or who have undergone cardiothoracic procedures are at especially high risk for clinically meaningful collapse after surgery.3PubMed Central. Perioperative Pulmonary Atelectasis: Part II. Clinical Implications
Then there is pain. A sternotomy (the vertical cut through the breastbone) and chest tube sites make it painful to take a full breath or to cough effectively. Without those deep breaths, collapsed regions of the lung tend to stay collapsed. This is why nurses and respiratory therapists start encouraging patients to use incentive spirometers and practice deep-breathing exercises as soon as they are awake enough to cooperate.
Opening the Pleura During Artery Harvesting
Many coronary artery bypass operations involve harvesting the left internal mammary artery, which runs just behind the front of the chest wall near the left lung. Surgeons sometimes need to open the pleural membrane, the thin sac surrounding the lung, to access this artery. Whether or not the pleura stays intact turns out to have a measurable effect on post-operative lung collapse.
A study of 1,141 bypass patients found that atelectasis on the fifth and seventh days after surgery was significantly less common in patients whose pleura had been left intact compared with those whose pleura had been opened.4PubMed Central. Effects of pleurotomy on respiratory sequelae after internal mammary artery harvesting A separate trial comparing the two approaches found that patients with preserved pleural integrity had better lung function measurements at five days, at discharge, and at 30 days, along with lower rates of both atelectasis and pleural effusion.5PubMed. Open Versus Closed Pleura Internal Mammary Artery Harvesting and Early Pulmonary Function After Coronary Artery Bypass Grafting
A third study quantified the severity difference. Among patients whose pleura was opened, about 75 percent had moderate or severe atelectasis on the second post-operative day, compared with roughly 32 percent in the group where the pleura was kept intact.6PubMed Central. Impact of Intact Pleura during Left Internal Mammary Artery Harvesting on Clinical Outcome By day five, the picture improved for both groups, but the gap persisted. The upshot is that when anatomically feasible, preserving the pleural membrane during mammary artery harvesting offers a real lung-function benefit.
Phrenic Nerve Injury and Diaphragm Paralysis
A less obvious but potentially serious driver of post-operative lung problems is damage to the phrenic nerve, which controls the diaphragm, the dome-shaped muscle responsible for most of your breathing effort. During open heart surgery, surgeons traditionally used ice slush to cool the heart and protect it from damage. That ice sits in the pericardial sac, right next to where the phrenic nerves run, and cold exposure can injure or temporarily paralyze them.
One prospective study of 133 patients found that when no effort was made to shield the phrenic nerves from ice slush, diaphragm paralysis occurred in 73 percent of patients. Life-threatening respiratory complications developed in 14 percent of the unshielded group, frequently requiring multiple reintubations, tracheostomy, or prolonged time on a ventilator.7PubMed. The effect of pericardial insulation on hypothermic phrenic nerve injury during open-heart surgery Another study of 100 patients confirmed the pattern: 82 percent of those who received topical ice slush had partial left lower lobe collapse within the first post-operative week, compared with 32 percent of those who did not receive ice. Diaphragm paralysis was seen in 32 percent of the ice group versus just 2 percent of the no-ice group.8The Annals of Thoracic Surgery. Diaphragm paralysis following cardiac surgery: Role of phrenic nerve cold injury
Modern cardiac surgery has largely moved away from liberal ice slush use, and many teams now employ insulating pads or cold-saline irrigation that is less extreme. But phrenic nerve injury can also result from mechanical stretching, electrocautery, or retractor pressure during surgery. It remains a recognized complication, particularly concerning in children and in adults with pre-existing lung disease such as COPD, where even modest diaphragm weakness can tip the balance toward respiratory failure.9Heart, Lung and Circulation. Phrenic Nerve Injury Complicating Cardiac Surgery
On-Pump Versus Off-Pump Surgery
Because cardiopulmonary bypass itself drives so much of the lung injury, surgeons have investigated whether performing coronary artery bypass without the heart-lung machine, called “off-pump” surgery, protects the lungs. The answer appears to be yes, at least for pulmonary function in the early recovery period. A study comparing the two approaches found that off-pump patients showed significantly greater improvement in lung function than on-pump patients.10PubMed. Off-pump versus on-pump coronary artery revascularization: effects on pulmonary function
Off-pump surgery is not suitable for every patient or every type of heart operation, and the decision involves trade-offs that go well beyond lung outcomes. But for patients at high baseline risk of respiratory complications, the pulmonary benefit of avoiding bypass may factor into the surgical plan.
What Surgical Teams Do to Prevent and Treat Collapse
The most important preventive measure happens in the operating room itself. “Recruitment maneuvers” are controlled episodes where the anesthesiologist temporarily inflates the lungs to high pressure, essentially popping open collapsed air sacs before the chest is closed. A meta-analysis of randomized trials found that patients who received recruitment maneuvers had a dramatically lower incidence of atelectasis. When higher-pressure maneuvers were used, the risk dropped by about 80 percent. Lower-pressure recruitment still cut the risk roughly in half. These maneuvers also reduced post-operative pneumonia and episodes of low oxygen without causing drops in blood pressure or cardiac output.11PubMed. Recruitment maneuvers to reduce pulmonary atelectasis after cardiac surgery: A meta-analysis of randomized trials
After surgery, the standard treatment toolbox includes several layers:
- Incentive spirometry and early mobilization: Getting patients sitting up, walking, and taking deep breaths is the first line of defense. Simply being upright reduces compression on the lower lobes.
- Positive-pressure breathing support: When atelectasis is already established, devices that deliver continuous positive airway pressure (CPAP) or noninvasive pressure-support ventilation (NIPSV) can help re-expand collapsed tissue. One trial comparing the two found that NIPSV improved radiological atelectasis scores in 60 percent of patients versus 40 percent with CPAP, though both approaches produced similar oxygenation levels and hospital stays.12PubMed. Continuous positive airway pressure versus noninvasive pressure support ventilation to treat atelectasis after cardiac surgery
- Bronchoscopy: In cases where a mucus plug physically blocks a bronchus, causing a lobe or an entire lung to collapse, a bronchoscope can be threaded into the airway to clear the obstruction. A case report described total left lung collapse during repair of an atrial septal defect in a child, caused by a mucous plug in the left main bronchus. Bronchoscopy performed while cardiopulmonary bypass continued was able to clear the blockage and fully re-expand the lung.13The Turkish Journal of Pediatrics. Development of bronchial mucous plugs under anesthesia and removal by bronchoscopy during open-heart surgery
How Lung Collapse Is Detected After Surgery
The traditional first look is a bedside chest X-ray, which most patients receive within hours of arriving in the ICU. Chest X-rays are convenient but not especially sensitive for spotting smaller areas of collapse, especially in a patient lying flat with surgical dressings and tubes in the way. Lung ultrasound is emerging as a more accurate alternative. A study comparing the two methods against CT scans as the gold standard found that ultrasound had a substantially higher diagnostic accuracy for detecting consolidation and atelectasis after cardiac surgery, with an area under the curve of 0.808 compared with 0.608 for chest X-ray.14PubMed Central. Lung ultrasound as a diagnostic tool for pulmonary consolidation and atelectasis after cardiac surgery Because ultrasound is portable, radiation-free, and can be repeated as often as needed, it is increasingly being used at the bedside in cardiac ICUs.
How Long the Lung Effects Last
The sharpest drop in lung function happens in the first week. One study found that vital capacity and the volume of air patients could force out in one second both fell to about 61 to 65 percent of pre-operative values within a week of surgery, a severe restrictive pattern.15PubMed Central. Long-term pulmonary functional status following coronary artery bypass grafting surgery Most patients experience a substantial recovery over the following months, but recovery may not be complete. The same study found that at six months, some measures of lung capacity and gas-exchange efficiency were still lower than they had been before surgery.
A separate study tracking patients for a full year after cardiac surgery found that forced vital capacity and the one-second forced exhalation volume remained about 4 to 5 percent below pre-operative levels at the 12-month mark. Blood oxygen saturation, on the other hand, had returned to baseline by that point.16PubMed Central. Pulmonary function and health-related quality of life 1-year follow up after cardiac surgery For most people, a 4 to 5 percent drop in lung capacity is not noticeable in daily life and does not limit activity. For someone with pre-existing lung disease, though, even a small permanent reduction can feel significant.
Risk Factors in Children
Pediatric heart surgery carries its own set of risk factors for post-operative atelectasis. A study of 254 children undergoing congenital heart surgery through a small right-sided incision identified younger age, higher body mass index, longer anesthesia time, and higher doses of certain muscle-relaxing and pain medications as independent risk factors for developing atelectasis. The severity of collapse also tended to worsen progressively during prolonged procedures.17Wiley. Risk Factors for Atelectasis Following Right Subaxillary Small-Incision Congenital Heart Surgery in Children
Children face an additional vulnerability: their airways are smaller, making them more susceptible to mucus plugging, and their chest walls are more compliant, meaning the lungs compress more easily under the weight of fluid or a distended heart. Phrenic nerve injury is also more consequential in small children because infants and toddlers rely almost entirely on the diaphragm for breathing, so even unilateral paralysis can cause serious respiratory distress. Careful anesthetic dosing, meticulous airway management, and early post-operative chest physiotherapy are especially important in this population.
The Difference Between Atelectasis and Pneumothorax
Patients and families often use the phrase “collapsed lung” to mean two quite different things, and the distinction matters. Atelectasis is a collapse caused by the lung tissue itself deflating or being compressed. It is extremely common after cardiac surgery, as all the evidence above shows. Pneumothorax, by contrast, is a collapse caused by air leaking into the space between the lung and the chest wall, which pushes the lung inward. Pneumothorax can occur after open heart surgery, particularly when the pleura has been opened during internal mammary artery harvesting, but it is far less frequent than atelectasis and is usually caught quickly by post-operative imaging. When a small pneumothorax is detected, it may resolve on its own; larger ones require a chest tube to drain the trapped air.
Pleural effusion, a buildup of fluid rather than air in the space around the lung, is another common post-operative finding that can compress lung tissue and mimic or worsen atelectasis. In the large audit mentioned earlier, pleural effusion was found in about 10.5 percent of cardiac surgery patients. All three conditions can coexist, and the treatment for each is different, which is why accurate imaging in the days after surgery is so important.