Air Leak

Etiology

The etiology of air leaks and ALS is varied. The following are some causes of ALS.[6][7][8]

Iatrogenic

• Mechanical ventilation and positive pressure ventilation - This is usually from barotrauma and polytrauma.
• Central venous catheterization - The insertion of a subclavian line might lead to the introduction of air into the pleural cavity. After placement of a subclavian line, a chest X-ray is necessary to confirm the proper position and also to check for the presence of pneumothorax.
• A surgical procedure in the thoracic cavity for example ligation of PDA or resection of a tumor in the thoracic cavity.
• Thoracoscopy either therapeutic or diagnostic has been linked to the development of air leaks.
• A laparoscopic procedure can cause the development of air leaks.
• Tracheostomy – If a false track is created with the insertion of a tracheostomy tube, subcutaneous emphysema can develop.

Lung Diseases 

The following lung diseases can cause air leak and ALS:

Restrictive lung diseases

• Adult respiratory distress syndrome
• Respiratory distress syndrome
• Cystic fibrosis
• Idiopathic pulmonary fibrosis

Obstructive lung diseases

• Asthma
• Bronchiolitis
• Chronic obstructive lung disease (COPD)

Other lung diseases

• Bronchopleural fistula
• Bullous lung diseased
• Necrotizing pneumonia
• Sarcoidosis
• Sarcoma
• Marfan syndrome
• Pulmonary hemorrhage
• Pulmonary contusion
• Tuberculosis
• Aspergillosis

Epidemiology

In a recent study with a total of 21,150 patients who underwent lung resection, the overall incidence of air leak complication is about 24.26% (95% confidence interval). [9][10]The following are identifiable risk factors:

• Resection type - lobectomy, segmentectomy, wedge resection
• Type of surgical approach
• Age
• Gender
• Presence of chronic obstructive pulmonary disease

The incidence of persistent air leak (PAL) is not known. In patients undergoing lung volume reducing surgery (LVRS), the incidence of PAL is as high as 46%.

After lobectomy, the incidence of PAL can range from 5.6% to 26% from various analyses to 34% to 38%.

Pathophysiology

To understand the pathophysiology of air leak and air leak syndrome, a basic understanding of pulmonary mechanics is important. The pressure in the pleural cavity is affected by the dynamics of chest wall movement. Changes in body posture and motion affect the pressure in the pleural cavity. The pleural pressure is related to the intrathoracic pressure. Pressure is also exerted on the conducting airway; this is known as the airway pressure. The difference in the airway pressure and the pressure in the pleural cavity is known as transpulmonary pressure. During spontaneous respiratory on a native airway, the transpulmonary pressure maintains a tidal ventilation secondary to the cyclic variability in pleural pressure. For patients on mechanical ventilation, the transpulmonary pressure that determines the tidal ventilation is controlled by cyclic changes in the mean airway pressure (PAW).[11][12][13]

The determination of the transpulmonary pressure in a patient breathing spontaneously or on mechanical ventilation requires the measurement of the intrathoracic pressure. This is achieved by using an esophageal balloon catheter position in the distal thirds of the esophagus. The airway pressure can be determined by measuring the pressure near the mouth or the endotracheal tube. Other use values for pulmonary dynamics are lung volume and airflow. Lung volume can be measured using plethysmography.

Measurement of the transpulmonary pressure requires the expiratory flow to be intermittently occluded after the insertion of the esophageal balloon catheter. The difference between the mouth, which is the airway pressure (PAW), and esophageal balloon pressure (PES) is the transpulmonary pressure (PTP).

In air leak and air leak syndrome, there is a presence of air in the pleural cavity that causes changes in the pleural pressure. Two types of pneumothoraxes are of clinical importance from this standpoint.

1. Stable pneumothorax - The presence of air in the pleural cavity with no significant change in the volume of air.
2. Unstable pneumothorax - The presence of air in the pleural cavity that is rapidly changing in volume and expanding. The presence of an air leak is mostly seen in pulmonary surgery but can arise spontaneously from a bleb or trauma.

During normal spontaneous respiration, the tidal volumes and airflow are determined by the cyclic variation in the pleural cavity pressure (PPL). The presence of air leaks will cause a decrease in lung volume, decreased airflow, and increased pleural pressure. This is related to an increase in lung resistance and elastance. The pressure in the pleural cavity is around 0 to -10 cm H20. Placement of a chest tube in the pleural cavity will reverse all the physiological changes associated with the accumulation of air in the pleural cavity. There will be lung expansion with improved airflow and decrease resistance and elastance. To evacuate the air associated with an air leak, a pressure greater than 10cm H20 is usually applied. In most practices, a pressure of -20 cm H20 is usually applied.

The presence of air leaks also affects oxygenation and carbon dioxide retention. The presence of a large air leak with no evacuation will compromise oxygenation. The loss of lung volume with air leak causes a "steal" phenomenon, with smaller lung volume compromising gas exchange and causing hypoxemia.

Large air leak and air leak syndrome negatively affect ventilation and gas exchange with carbon dioxide retention. Evacuation of the air leak will remove carbon dioxide and decrease the partial pressure of carbon dioxide in the blood, causing respiratory alkalosis.

In primary spontaneous pneumothorax, bullae are the primary culprit in about 76% to 100% of cases. This is usually from smoking. Bullae formation follows a particular pathway. Destruction of the elastic fibers in the lung is induced by macrophages and neutrophils, which are activated by exposure to smoke inhalation. The breakdown of elastin causes a disbalance between the oxidant and the antioxidant system as well as the protease-antiprotease system. Once the bullae are formed, they cause inflammation of the airway. The obstruction from inflammation causes the bullae to rupture, causing pneumomediastinum and later pneumothorax.[14][15]

In patients on mechanical ventilation on high-pressure settings, barotrauma causes leakage of air into the perivascular interstitium. At a critical level of the pressure gradient between the alveolus and the interstitial space, the alveolus ruptures, and air can escape and accumulate in the mediastinum pericardium or pleural cavity. The critical pressure that gives rise to this all depends on (1) the severity of lung injury and (2) the tidal volume used in mechanical ventilation.

To evacuate pneumothorax secondary to an air leak or ALS, a chest tube with drainage usually is connected to the pleural cavity. The level of fluid in the fluid column in the chest tube drainage system changes with the respiratory mechanism. During inspiration, the column rises; during expiration, the level falls. Loss of variability in the fluid column is associated with a loss of connection between the chest tube system and pleural cavity. The following are causes: 

• Tube kinking
• Blood clot
• Pus or fibrin
• System blocks

History and Physical

The history and physical examination can help to elucidate the cause of air leaks.

Symptoms

The onset, duration, and location of symptoms and other associated signs should be elicited from the patient.

History

From the history, the clinician should be able to determine the underlying disease that caused the development of air leak syndrome.

Wheezing and difficulty breathing is highly suggestive of obstructive lung diseases like asthma and COPD.

Coughing, dyspnea, and fever might point towards pneumonia or acute respiratory distress syndrome.

Weight loss, hemoptysis, and nighttime fever might indicate tuberculosis or lung cancer. A history of recent thoracic surgery, especially procedures that involve the bronchi, lungs, and pleural cavity, might be related to the development of air leak and ALS.

In an intubated patient on mechanical ventilation at high settings, a sudden change in the clinical status of the patient, like the development of hypoxia, desaturation, and change in hemodynamics, might be related to the development of pneumothorax.

Chief Complaint

Most patients with pneumothorax will have a sudden onset of chest pain with dyspnea. If the pneumothorax is very large, the discomfort and respiratory distress might be severe.

Physical Assessment

The physical assessment of a patient with an air leak, ALS begins with an evaluation of the general appearance. If the air leak is small, the patient might be totally asymptomatic. The presence of moderate to large size pneumothorax might produce the following physical signs:

• Dyspnea
• Tachypnea
• Tachycardia

Subcutaneous emphysema produces a painless swelling of the skin and subcutaneous tissue. Palpation of the skin produces the feeling of tissue paper in the hands. Subcutaneous emphysema may track deeper into the mediastinum, peritoneum, retroperitoneal space, scrotal wall, and even the extremities.

Percussion of the chest wall will elicit hyper-resonance in the area of the chest cavity filled with air. Auscultation might demonstrate diminished breath sounds or total absence if the pneumothorax is very large.

Evaluation

The evaluation and diagnosis of air leak start with a detailed history and physical examination. Ancillary studies are necessary to confirm the diagnosis.[2][6][12]

Chest X-ray

This is the most common and readily available study for the diagnosis of air leaks. The presence of a radiolucent area of air in the lung field with the absence of lung marking is highly suggestive of a pneumothorax. Pneumothorax can have different appearances in a supine and upright chest X-ray. Pneumothoraxes in a patient on mechanical ventilation might enlarge and become a tension pneumothorax. Radiological signs in tension pneumothorax are a mediastinal shift, loss of lung volume or “shrinking" of the lung, flattening of the heart, and vascular shadow.

Pneumomediastinum radiologically can be seen as a column of air in the mediastinum. If the amount of air is large enough, it can displace the thymus to produce the thymic sail sign.

Pneumopericardium is seen as a collection of air around the pericardial sac on routine chest X-ray.

Chest Ultrasound

This imaging is gaining popularity in the diagnosis of pneumothoraxes. It has close to 95% sensitivity and 100% specificity for the diagnosis of pneumothorax when compared to a CT scan.

It can be useful for the diagnosis of pneumothorax not seen on plain X-ray. The presence of subcutaneous emphysema can impair the accuracy of the ultrasound reading.

The sonographic sign of pneumothorax is the absence of lung sliding. In the presence of a pneumothorax. This sliding is absent. In the ultrasonographic assessment to identify pneumothorax, two ribs are identified with the pleural space between them. The normal back-and-forth movement or "shimmering" of the pleural line is usually absent.

CT Scan

CT scan is a useful imaging study for a patient with a persistent air leak. CT of the chest helps to differentiate bullous disease of the lung from pneumothorax. It also helps to differentiate other lung and pleural pathologies. CT scan is considered the gold standard in the diagnosis of air leak and ALS. The risk of CT is radiation. Also, this imaging study can be challenging on a critically ill patient on mechanical ventilation and vasoactive drips because the transport of the patient to facilitate the imaging study can be potentially dangerous.

Treatment / Management

The presence of air leak and ALS in a patient is sometimes a diagnostic and management challenge. A review of the literature did not show any specific guidelines for management. The overall consensus is to get a surgical consultation if the air leak persists after 4 days.[6][16][17](A1)

Simple Aspiration

Simple aspiration is the recommended therapy for most primary pneumothoraxes. Aspiration of air from the pleural cavity is performed in a sterile condition. The site of needle insertion is the fourth or fifth intercostal space along the anterior, middle auxiliary line. After accessing the pleural space with the needle, usually an 18-gauge, a three-way stopcock is attached. A 50 mL syringe is attached to the stop clock, and the other end is attached to an intravenous tubing with is connected to a water seal. Aspiration is completed when the practitioner feels a resistance to pulling, excessive coughing from the patient, or a sensation that the lung has fully expanded.

Needle Thoracostomy

For tension pneumothorax which is a medical emergency, it is recommended to use a needle that is about 3 to 6 cm long as the thickness of the chest wall is around 4 to 4.5 cm. The site of insertion is the second intercostal space along the midclavicular line. The cannula should be left in place and, if possible, connected to an underwater seal. The presence of an air bubble will indicate proper functioning.  

Chest Tube Insertion

If simple aspiration fails, the next option is to insert a chest tube and connect it to a chest tube drainage system. A large-bore or small-bore tube can be inserted. If there is no associated hemothorax, a small-bore tube is adequate. The most common site for insertion is the middle auxiliary line. This minimizes the potential damage to the internal mammary artery as well as the soft tissue of the breast. The chest tube with the drainage system should be in place until there is full lung re-expansion and no further air leak. If suction is required for the drainage of air from the pleural cavity, a pressure of between 10 to 20 cm H20 is applied.

Prevention

To prevent reaccumulation or recurrence of pneumothoraxes, three methods can be utilized.

1. Medical pleurodesis This is the instillation of bleomycin or talc into the pleural cavity. This creates an inflammatory response and causes the sealing of the visceral and parietal pleura, and permanently seals the pleural cavity. 
2. Pleural tentingThis idea was first suggested by Miscall in 1956 and Hansell in 1957. It is also called extrapleural apicolysis and parietal pleurolysis. It is performed at the same time with lobectomy. The parietal pleura is partially separated from the chest wall. This tent or sheet of pleural tissue is then attached to the surface of the non resected lung. This tent separates the non resected lung from the extrapleural space that is surgically created. Phrenoplasty is sometimes done in conjunction with pleural tenting. The pericardium and diaphragm are divided allow the hemidiaphragm to rise, thus reducing the pleural dead space. The function of the diaphragm is not impaired by this procedure.
3. Surgical PleurodesisThis method entails the stripping and abrasion of the parietal pleural. An inflammatory response is produced that also seals the pleural cavity.

Prolonged air leak (PAL) is the presence of an air leak that persists for more than 4 to 5 days postoperatively. PAL is the most common complication following operative intervention in the thoracic cavity, followed by pneumonia, respiratory failure, and bleeding. The mortality is between 1% to 12%.

In PAL, the first thing to determine is the origin of the leak. Air leaks can occur from the following structures:

Alveolus

This air leak originates from a peripheral lesion via the alveolus.

Bronchial Structure

This air leak arises from the bronchial stump or anastomosis, creating a bronchopleural fistula. If this is the case, a bronchoscopy is indicated. In most instances, air leak originates from the alveolus, and the initial treatment should be directed towards the correction of alveolar air leak.

Treatment of PAL (Persistent Air Leak)

The pneumoperitoneum method has been in existence since the early eighties. During surgery, if, after resection of the lung, the remaining part of the lung cannot completely fill the chest cavity, PAL can develop. To correct this, a pneumoperitoneum is artificially created through a transdiaphragmatic route which is closed by a pouch string suture. Air leaks will resolve within a few days, and the peritoneal air is absorbed within a couple of weeks.

Blood Patch

The infusion of autologous blood into the pleural cavity as a sealant has been used to treat persistent PAL.

Intrabronchial Valve

This is a less invasive therapy where a one-way endobronchial valve is introduced into the bronchus for the treatment of bronchopleural fistula.

Heimlich Valve (Flutter Valve)

Henry Jay Heimlich is an American who invented the Heimlich valve. It is a flutter valve that has a one-way valve. This allows air to flow in one direction. Air from the pleural cavity enters the valve when the sleeve opens and closes to prevent backward flow of air from the valve. It can be connected to the tube in the pleural cavity, and the patient can be managed in an outpatient setting. The use of this valve can significantly reduce the length of inpatient stay.

Surgical Intervention

If all these interventions are not successful, a video-assisted thoracoscopy (VAT) is carried out. VAT can be used to visualize the pleural cavity, identify the leak, and apply sclerosing agents. In some instances, pleurotomy is done.[18][19][20](A1)

Differential Diagnosis

The differential diagnosis of air leak and air leak syndrome should address all of the causes of pneumothorax, including the following:

1. Iatrogenic
2. Spontaneous
3. Traumatic
4. Direct and indirect causes of pneumothoraxes

Primary and secondary causes of pneumothoraxes also should be factored in the differential diagnosis.