Pleura: Anatomy, Function, and Clinical Significance

The pleura is a thin membrane that covers the lungs and lines the inner surface of the chest. Although it occupies very little space, it is essential for normal breathing because it allows the lungs to move smoothly and remain mechanically connected to the chest wall.

The pleural space normally contains only a small amount of fluid and remains under negative pressure.

When air, blood, pus, lymphatic fluid, or excess serous fluid enters this space, lung expansion may become restricted and respiratory function can deteriorate.

What Is the Pleura?

The pleura consists of two thin, smooth serous membranes associated with each lung. These membranes are known as the visceral pleura and the parietal pleura. Together, they form a low-friction system that allows the lungs to expand and recoil within the thoracic cavity.

The two pleural layers are normally positioned very close together. A thin layer of fluid between them permits movement while helping the surfaces remain attached. This relationship allows the lungs to follow the movements of the chest wall and diaphragm during breathing.

Each lung is enclosed within its own pleural sac. The right and left pleural spaces are normally separated by the mediastinum and do not communicate with one another. As a result, a pleural disorder may affect only one side of the chest.

Visceral Pleura

The visceral pleura directly covers the outer surface of the lungs. It closely follows the contours of the lung and extends into the fissures that separate the lobes.

Because the visceral pleura is firmly attached to lung tissue, it moves with the lung during inspiration and expiration. It cannot normally be separated from the lung without damaging the underlying tissue.

The visceral pleura is structurally different from the parietal pleura. It contains a relatively dense layer of connective tissue and blood vessels. However, it does not contain the lymphatic stomata that are present in the parietal pleura.

The visceral pleura also lacks pain-sensitive sensory innervation. For this reason, irritation or manipulation of the visceral surface does not usually cause sharp pleural pain. Most pain associated with pleural inflammation originates from the parietal pleura.

Parietal Pleura

The parietal pleura lines the structures surrounding the lungs. It covers the inner chest wall, the upper surface of the diaphragm, and the lateral borders of the mediastinum.

The parietal pleura is divided into regions based on the structure it covers:

• The costal pleura lines the ribs and inner chest wall.
• The diaphragmatic pleura covers the thoracic surface of the diaphragm.
• The mediastinal pleura borders the mediastinum.
• The cervical pleura extends over the apex of each lung into the lower neck.

The visceral and parietal pleura become continuous at the lung hilum. The hilum is the area where the major bronchi, pulmonary blood vessels, lymphatic vessels, and nerves enter or leave the lung.

The parietal pleura contains capillaries and lymphatic openings called stomata. These structures play an important role in pleural fluid production and removal.

Sensory Innervation of the Pleura

The parietal pleura is richly supplied with sensory nerves and is highly sensitive to pain. The location of discomfort depends on which area of the parietal pleura is irritated.

The costal pleura is supplied by intercostal nerves. Inflammation in this region usually produces localized chest pain that may follow the distribution of an intercostal space.

The peripheral portion of the diaphragmatic pleura is also supplied by intercostal nerves. However, the central diaphragmatic pleura is supplied by the phrenic nerve. Irritation in this central region may produce referred pain in the shoulder or neck.

Note: This referred pain occurs because sensory fibers from the phrenic nerve enter the spinal cord at cervical levels that also receive sensation from the shoulder region.

The Pleural Space

The pleural space is located between the visceral and parietal pleura. Under normal conditions, it is considered a potential space rather than an open cavity because the two membranes remain closely opposed.

Only a small amount of pleural fluid is normally present. An average adult may have approximately 8 mL of fluid in each hemithorax, although the exact amount varies.

This fluid forms a thin lubricating film that allows the pleural surfaces to slide across one another with minimal friction. At the same time, surface tension within the fluid helps keep the layers attached.

The relationship is sometimes compared to two wet pieces of glass. The glass surfaces can slide over one another easily, but they resist being pulled apart. Similarly, the pleural membranes move smoothly while remaining mechanically linked.

Although the normal pleural space is extremely narrow, it can expand during disease. Large quantities of air, blood, pus, or other fluid may collect within it.

Normal Pleural Pressure

Pressure within the pleural space is normally lower than atmospheric pressure. This is called negative intrapleural pressure or subatmospheric pleural pressure.

Negative pleural pressure results from opposing elastic forces. The lungs naturally tend to recoil inward because of their elastic tissue and surface tension. The chest wall tends to recoil outward. These forces pull in opposite directions and create negative pressure between the pleural surfaces.

Normal pleural pressure generally ranges from approximately 0 to −5 cm H2O during quiet breathing, although the value changes throughout the respiratory cycle.

During inspiration, the diaphragm contracts and moves downward. The chest cavity enlarges, pulling the parietal pleura outward. Because the visceral pleura remains attached through the pleural fluid layer, the lungs are pulled outward as well.

As the lungs expand, alveolar pressure falls, allowing air to flow through the airways and into the lungs. During expiration, the diaphragm relaxes and the chest cavity becomes smaller. The elastic recoil of the lungs helps move air out. The pleural layers continue to slide against one another throughout this process.

Note: Pleural pressure is not uniform throughout the chest. In an upright person, it is more negative near the lung apex and less negative near the base. Gravity and the weight of the lung contribute to this pressure gradient.

Pleural Fluid Formation and Removal

Pleural fluid is mainly produced by capillaries in the parietal pleura. Fluid moves from these capillaries into the pleural space through normal filtration processes. The fluid is primarily removed by lymphatic stomata in the parietal pleura. These openings connect the pleural space with lymphatic vessels that transport excess fluid away from the chest.

Pleural fluid is normally produced at a rate of approximately 0.01 mL/kg per hour. The lymphatic system can remove fluid at a much greater rate, potentially close to 0.20 mL/kg per hour. This means lymphatic drainage capacity may be nearly 20 times greater than the usual rate of pleural fluid formation. Pleural fluid therefore does not accumulate under normal conditions.

Note: A pleural effusion develops when fluid production exceeds lymphatic drainage or when lymphatic removal becomes impaired.

Functions of the Pleura

The pleura performs several important mechanical and protective functions.

• Reducing Friction: The lubricating pleural fluid minimizes friction between the lungs and surrounding structures. Without this fluid, the pleural surfaces would rub directly against one another during every breath.
• Supporting Lung Expansion: Negative pleural pressure helps keep the lungs expanded against the chest wall. This pressure opposes the natural tendency of the lungs to recoil inward.
• Transmitting Chest-Wall Movement: The pleural fluid and pressure relationship allow movement of the chest wall and diaphragm to be transmitted to the lungs. When the thoracic cavity expands, the lungs expand with it.
• Separating the Lungs: Each lung is enclosed in a separate pleural sac. This separation may help prevent a disorder affecting one pleural space from immediately spreading to the other side.

Pleurisy

Pleurisy, also called pleuritis, is inflammation of the pleural membranes. It may develop with bacterial pneumonia, viral infection, tuberculosis, fungal disease, pulmonary embolism, autoimmune disorders, trauma, or malignancy.

When the pleura becomes inflamed, the normally smooth surfaces become rough. Movement during breathing causes the inflamed membranes to rub together.

The most common symptom is sharp, stabbing chest pain that worsens with deep inspiration. The pain may also become worse with coughing, sneezing, or movement of the chest.

Patients may begin breathing rapidly and shallowly to reduce pleural movement and discomfort. The pain may be localized to one area or referred to the shoulder when the diaphragmatic pleura is involved.

Pleural Friction Rub

A pleural friction rub is an abnormal sound produced when inflamed pleural surfaces move against each other. It may be described as:

• Grating
• Creaking
• Rasping
• Rough
• Leather-like

The sound may be heard during inspiration, expiration, or both. It is often localized over the area where the patient reports pain.

A pleural friction rub does not usually clear after coughing or suctioning. This helps distinguish it from rhonchi caused by secretions in the larger airways.

Pleural Effusion

A pleural effusion is an abnormal accumulation of fluid within the pleural space. The fluid separates the visceral and parietal pleura and may compress the underlying lung.

Small effusions may produce few symptoms. Larger effusions can restrict lung expansion, reduce lung volume, increase the work of breathing, and impair gas exchange.

Symptoms and Physical Findings

Common findings include:

• Dyspnea
• Pleuritic chest discomfort
• Increased work of breathing
• Reduced chest movement on the affected side
• Decreased or absent breath sounds
• Decreased tactile fremitus
• Dullness to percussion
• Hypoxemia

Fluid in the pleural space dampens the transmission of sound and vibration from the lung to the chest wall. This explains why breath sounds and tactile fremitus are commonly reduced.

Percussion over pleural fluid produces a dull note because fluid is denser than normally aerated lung tissue.

A large effusion may push the trachea, heart, and mediastinum away from the affected side. However, if the effusion occurs with significant atelectasis or lung-volume loss, mediastinal structures may be pulled toward the abnormal side. The direction of shift must therefore be interpreted along with other findings.

Transudative Pleural Effusion

A transudative effusion develops when the pleural membranes are relatively normal but systemic pressure or protein abnormalities cause fluid to move into the pleural space.

Common causes include:

• Congestive heart failure
• Cirrhosis
• Nephrotic syndrome
• Severe hypoalbuminemia
• Atelectasis
• Some forms of lymphatic obstruction

Congestive Heart Failure

Congestive heart failure is one of the most common causes of pleural effusion. Increased pulmonary venous pressure raises fluid pressure within the pulmonary circulation.

Fluid may move into the lung interstitium and then enter the pleural space. Elevated systemic venous pressure may also interfere with lymphatic drainage.

Effusions caused by heart failure are often bilateral and relatively small. However, they may become large enough to compress a significant portion of one or both lungs.

Note: Treatment of the underlying heart failure frequently causes the fluid to resolve.

Hypoalbuminemia and Nephrotic Syndrome

Plasma proteins, particularly albumin, help maintain oncotic pressure within the blood vessels. When albumin levels fall significantly, fluid is more likely to leave the circulation and enter tissues or body cavities.

Severe hypoalbuminemia and nephrotic syndrome may therefore contribute to pleural effusion, peripheral edema, and other fluid accumulations.

Hepatic Hydrothorax

Patients with advanced liver disease may develop ascites and pleural effusion. Ascitic fluid may pass through small defects in the diaphragm because abdominal pressure is greater than pleural pressure.

This condition is called hepatic hydrothorax. It occurs most commonly on the right side.

Atelectasis

Atelectasis may create more negative pressure within part of the pleural space. This can draw a small amount of fluid into the region and contribute to effusion formation.

Exudative Pleural Effusion

An exudative effusion develops because of inflammation, infection, injury, or malignancy involving the lung or pleura.

Common causes include:

• Bacterial pneumonia
• Tuberculosis
• Viral pleurisy
• Malignancy
• Pulmonary embolism
• Connective tissue disease
• Chest trauma
• Thoracic surgery
• Gastrointestinal disease
• Medication reactions

Note: Inflammation increases capillary permeability, allowing proteins, inflammatory cells, and fluid to enter the pleural space.

Parapneumonic Effusion

An effusion associated with bacterial pneumonia is called a parapneumonic effusion. Some of these effusions remain sterile and resolve with antibiotic therapy.

Others become complicated because bacteria enter the pleural fluid, glucose decreases, pH falls, and fibrin begins dividing the collection into separate compartments.

Empyema

Empyema is infected pleural fluid containing pus. It usually develops as a complication of pneumonia, thoracic surgery, trauma, or another infection.

Empyema may produce fever, chest pain, dyspnea, leukocytosis, and systemic illness. Drainage may appear thick, cloudy, yellow, or green.

Treatment commonly includes antibiotics and pleural drainage. Loculated or organized collections may require more advanced interventions.

Malignant Pleural Effusion

A malignant pleural effusion occurs when cancer involves the pleura or interferes with lymphatic drainage. Lung cancer, breast cancer, lymphoma, and metastatic cancers are common causes.

Malignant effusions frequently recur and may prevent the lung from expanding normally. Repeated drainage, an indwelling pleural catheter, or pleurodesis may be considered.

Other Pleural Fluid Collections

Not every pleural collection is a simple transudative or exudative effusion.

Hemothorax

A hemothorax is an accumulation of blood in the pleural space. It may result from chest trauma, surgery, vascular injury, malignancy, or rupture of a blood vessel. Blood in the pleural space may compress the lung and contribute to hypovolemia. Drainage is usually red or dark red.

Significant hemothorax often requires chest tube placement and close monitoring of drainage volume and hemodynamic status.

Chylothorax

A chylothorax is the accumulation of chyle, a lymphatic fluid rich in fat. It commonly results from disruption or obstruction of the thoracic duct.

Causes may include thoracic surgery, trauma, lymphoma, malignancy, or congenital abnormalities. The fluid often appears white or milky because of its fat content. However, appearance alone is not sufficient for diagnosis.

Effects of Pleural Effusion on Gas Exchange

Moderate or large pleural effusions compress the adjacent lung. This decreases the amount of lung tissue available for ventilation.

Some blood may continue flowing through compressed or poorly ventilated regions. This creates ventilation-perfusion mismatch and may cause hypoxemia.

The patient may compensate by increasing respiratory rate and effort. If the effusion becomes very large, respiratory distress may develop.

Large pleural collections can also increase intrathoracic pressure and compress major veins. Reduced venous return may decrease cardiac output, particularly when the accumulation is rapid or under pressure.

Diagnosing Pleural Effusion

Pleural effusions may be identified with chest radiography, thoracic ultrasound, or computed tomography.

Chest Radiography

On an upright chest radiograph, pleural fluid commonly settles at the base of the lung. Early findings may include blunting of the costophrenic angle.

As the collection enlarges, a curved upper border known as a meniscus may appear. A very large effusion may produce extensive opacity throughout the affected hemithorax.

Thoracic Ultrasound

Ultrasound is highly useful for detecting pleural fluid, including smaller collections that may not be obvious on chest radiography.

It can help:

• Confirm the presence of fluid
• Estimate the size of the collection
• Distinguish fluid from consolidated lung
• Identify loculations
• Guide thoracentesis
• Reduce the risk of puncturing the lung

Computed Tomography

Computed tomography provides detailed information about the pleura, lungs, mediastinum, and chest wall. It may be useful when pleural thickening, malignancy, infection, trauma, loculated fluid, or another underlying disorder is suspected.

Thoracentesis

Thoracentesis is a procedure in which a needle or catheter is inserted through the chest wall and into the pleural space.

It may be performed for diagnostic or therapeutic purposes.

Diagnostic Thoracentesis

Diagnostic thoracentesis obtains pleural fluid for laboratory examination. Testing may include:

• Protein
• Lactate dehydrogenase
• Glucose
• pH
• Red and white blood cell counts
• Differential cell count
• Gram stain
• Bacterial culture
• Tuberculosis testing
• Cytology for malignant cells
• Triglycerides when chylothorax is suspected

Note: These results help determine whether the effusion is transudative or exudative and may identify infection, malignancy, bleeding, or lymphatic fluid.

Therapeutic Thoracentesis

Therapeutic thoracentesis removes fluid that is causing dyspnea, hypoxemia, pain, or significant lung compression.

Fluid removal may improve lung expansion and decrease the work of breathing. However, removing a large volume too rapidly may increase the risk of re-expansion pulmonary edema.

Patient Positioning

The patient is commonly seated upright at the edge of the bed and asked to lean forward over an over-bed table. Another option is to sit backward on a chair with the arms and head supported on the chair back.

A patient who cannot sit may be positioned on the side with the unaffected lung downward, depending on the clinical situation and chosen procedure site. The patient should remain still and avoid coughing while the needle is in place.

Needle Placement

The needle or catheter is generally inserted immediately above the upper border of a rib.

The intercostal vein, artery, and nerve travel along the lower border of each rib. Inserting the needle above the rib reduces the risk of injuring these structures. Ultrasound guidance improves site selection and reduces the risk of complications.

Complications of Thoracentesis

Possible complications include:

• Pneumothorax
• Hemothorax
• Intercostal vessel injury
• Infection
• Re-expansion pulmonary edema
• Vasovagal reaction
• Hypotension
• Subcutaneous emphysema
• Air embolism
• Injury to the liver or spleen
• Coughing or respiratory distress

Note: Patients should be monitored during and after the procedure for new chest pain, hypoxemia, dyspnea, diminished breath sounds, hemoptysis, hypotension, or other signs of deterioration.

Pneumothorax

A pneumothorax is the presence of air in the pleural space. The air separates the pleural surfaces and disrupts negative intrapleural pressure.

Once the normal pressure relationship is lost, the lung recoils inward and may partially or completely collapse.

Causes of Pneumothorax

Pneumothorax may result from:

• Chest trauma
• Rupture of a pulmonary bleb or bulla
• Mechanical ventilation
• Barotrauma
• Volutrauma
• Central venous catheter placement
• Lung biopsy
• Thoracentesis
• Thoracic surgery
• Severe emphysema

Note: A spontaneous pneumothorax occurs without an obvious external injury. It may develop when a small bleb near the lung surface ruptures.

Clinical Findings

Common findings include:

• Sudden pleuritic chest pain
• Dyspnea
• Decreased chest movement on the affected side
• Reduced or absent breath sounds
• Reduced tactile fremitus
• Hyperresonance to percussion
• Tachycardia
• Hypoxemia
• Subcutaneous emphysema

Note: Subcutaneous emphysema occurs when air enters the soft tissues. It may produce swelling and a crackling sensation called crepitus.

Radiographic Findings

On chest radiography, pleural air appears more radiolucent, or darker, than normal lung tissue.

A thin pleural line may be visible, with no vascular markings beyond it. The collapsed lung may appear displaced inward toward the hilum.

Correct film exposure is important because an overexposed image may make a small pneumothorax difficult to recognize.

Pneumothorax in Mechanically Ventilated Patients

Positive-pressure ventilation can force air through damaged lung tissue and into the pleural space. A sudden rise in peak inspiratory pressure and plateau pressure may indicate decreased lung compliance caused by a pneumothorax.

During volume-controlled ventilation, both pressures may increase while the set tidal volume continues to be delivered. During pressure-controlled ventilation, the delivered tidal volume may fall because the ventilator cannot overcome the reduced compliance within the selected pressure limit.

Sudden hypoxemia, hypotension, unilateral loss of breath sounds, or unexplained ventilator alarms should raise immediate concern.

Treatment of Simple Pneumothorax

Treatment depends on the size of the pneumothorax, the cause, the patient’s symptoms, and the patient’s overall condition.

A small pneumothorax in a stable patient may be treated with supplemental oxygen and close observation. Pleural air may gradually be reabsorbed.

Larger, symptomatic, traumatic, persistent, or ventilator-associated pneumothoraces generally require drainage.

Treatment options may include:

• Observation
• Supplemental oxygen
• Needle aspiration
• Small-bore catheter placement
• Chest tube drainage

Note: Restoring negative pleural pressure allows the lung to re-expand.

Tension Pneumothorax

A tension pneumothorax occurs when air enters the pleural space but cannot escape. Pressure increases with each breath.

The expanding air collection compresses the affected lung and shifts the mediastinum toward the opposite side. It may also compress the heart and major blood vessels.

Venous return to the heart decreases, causing reduced cardiac output, hypotension, obstructive shock, and possible cardiac arrest.

Signs of Tension Pneumothorax

Important findings include:

• Sudden severe respiratory distress
• Rapid hypoxemia
• Hypotension
• Tachycardia
• Markedly reduced or absent breath sounds on one side
• Unilateral hyperresonance
• Reduced chest movement on the affected side
• Tracheal deviation away from the affected side
• Distended neck veins in some patients
• Worsening ventilator pressures
• Rapid reduction in tidal volume during pressure-controlled ventilation

Note: Tracheal deviation is generally a late sign and should not be required before treatment.

Emergency Treatment

Treatment must not be delayed for imaging when an unstable patient has findings strongly suggesting tension pneumothorax.

Emergency needle decompression is performed to release trapped air. One described approach uses a large-bore catheter placed in the second or third intercostal space at the midclavicular line, passing over the upper border of the rib.

Clinical practice may also use an anterolateral approach based on patient anatomy, local protocol, and available equipment.

A rush of air and improvement in the patient’s condition support successful decompression. Needle decompression is temporary. A chest tube must then be inserted for definitive and continuous drainage.

Chest Tube Drainage

Chest tubes provide ongoing removal of air, blood, pus, or other fluid from the pleural space. A tube intended to remove air is generally directed toward the upper chest because air rises.

A tube intended to remove fluid is directed toward a dependent posterior or inferior region because fluid settles with gravity. After insertion, the chest tube is secured and connected to a pleural drainage system.

Components of a Chest Drainage System

Most chest drainage systems contain three main components.

Collection Chamber

The collection chamber receives pleural fluid and allows the drainage volume to be measured. The amount, color, and character of the drainage should be monitored and documented. A sudden increase in bloody drainage may indicate active bleeding and must be reported promptly.

Water-Seal Chamber

The water seal functions as a one-way valve. It allows air to leave the pleural space but prevents atmospheric air from returning to the patient. Traditional wet systems commonly use a water-seal depth of approximately 2 cm.

The fluid level may rise and fall with breathing or with the mechanical ventilator cycle. This movement is called tidaling. Absence of tidaling may indicate lung re-expansion, obstruction, a kinked tube, or incorrect system position. The finding must be interpreted in context.

Suction-Control Mechanism

Suction may be applied when additional negative pressure is needed to evacuate pleural air or fluid.

In a wet suction system, the suction-control chamber may be filled to a prescribed level, often 20 cm H2O. Wall suction is increased until gentle bubbling occurs. In a dry suction system, the prescribed suction level is set using a mechanical regulator.

Increasing wall suction does not necessarily increase the amount of suction delivered to the patient when the drainage unit is functioning properly.

Bubbling and Air Leaks

Bubbling in the water-seal chamber may indicate that air is leaving the pleural space. Intermittent bubbling may occur with coughing or exhalation when a pneumothorax is resolving.

Continuous bubbling may indicate:

• An active pleural air leak
• A bronchopleural fistula
• A loose connection
• A leak within the drainage system

Note: The entire system should be assessed when continuous bubbling is observed. When bubbling stops, it may indicate that the air leak has healed. However, it could also mean the tube is obstructed or kinked.

Chest Tube Safety

The drainage unit should always remain upright and below the level of the patient’s chest.

Tubing should be free from:

• Kinks
• Dependent loops
• Compression
• Clots
• Obstruction

The chest tube should not be routinely clamped. Clamping may trap air within the pleural space and cause a tension pneumothorax. The tube should also not be stripped aggressively because this may create excessive negative pressure.

During transport, the drainage system should remain below chest level and secured in an upright position.

After chest tube removal, the patient should be monitored for recurrence of pneumothorax or pleural fluid. New dyspnea, chest pain, reduced breath sounds, hypoxemia, or crepitus may indicate a complication.

Pleurodesis

Pleurodesis is a procedure used to cause the visceral and parietal pleura to adhere to one another. A chemical agent or mechanical irritation produces inflammation and fibrosis, eliminating the pleural space.

Pleurodesis may be used for recurrent pneumothorax or recurrent malignant pleural effusion. The goal is to prevent air or fluid from repeatedly accumulating between the pleural layers.

Clinical Assessment of Pleural Disorders

Pleural disorders often produce recognizable patterns during physical assessment.

Breath Sounds

Air or fluid in the pleural space separates the lung from the chest wall. Breath sounds are therefore commonly decreased or absent over the affected area.

Tactile Fremitus

Tactile fremitus is usually reduced because pleural air or fluid interferes with the transmission of vocal vibrations.

Percussion

The percussion note depends on the material within the pleural space.

• Air produces hyperresonance.
• Fluid produces dullness.
• Blood and pus also produce dullness.

Chest Movement

The affected side may move less during breathing because the underlying lung is compressed or collapsed.

Mediastinal Shift

Large accumulations of air or fluid may push the mediastinum away from the affected side. Conditions involving severe loss of lung volume, such as major atelectasis, may pull the mediastinum toward the affected side.

Note: This distinction is important when interpreting chest radiographs and physical findings.

Role of the Respiratory Therapist

Respiratory therapists often participate in the assessment and management of patients with pleural disorders.

Responsibilities may include:

• Evaluating breath sounds and chest movement
• Monitoring oxygen saturation and vital signs
• Recognizing signs of pneumothorax or tension pneumothorax
• Assessing ventilator pressure and volume changes
• Administering supplemental oxygen
• Assisting with thoracentesis
• Monitoring patients during pleural procedures
• Observing chest drainage systems
• Measuring and documenting drainage
• Identifying air leaks or tubing obstruction
• Preparing emergency equipment
• Supporting patients during chest tube insertion or removal

Note: Rapid recognition is especially important in mechanically ventilated patients because a pneumothorax may enlarge quickly under positive pressure.

Pleura Practice Questions

1. What is the pleura?
The pleura is a two-layered serous membrane that covers the lungs and lines the inside of the thoracic cavity.

2. What are the two layers of the pleura?
The two layers are the visceral pleura and the parietal pleura.

3. Which pleural layer directly covers the surface of the lungs?
The visceral pleura directly covers the lungs and extends into the fissures between the lobes.

4. Which pleural layer lines the inner surface of the chest wall?
The parietal pleura lines the chest wall, diaphragm, and mediastinum.

5. Where do the visceral and parietal pleura become continuous?
They become continuous at the hilum of the lung.

6. What structures pass through the lung hilum?
The major airways, blood vessels, lymphatic vessels, and nerves pass through the hilum.

7. What is the costal pleura?
The costal pleura is the portion of the parietal pleura that lines the ribs and inner chest wall.

8. What is the diaphragmatic pleura?
The diaphragmatic pleura is the portion of the parietal pleura that covers the upper surface of the diaphragm.

9. What is the mediastinal pleura?
The mediastinal pleura is the portion of the parietal pleura that borders the mediastinum.

10. Which nerves provide sensory innervation to the costal pleura?
The intercostal nerves provide sensory innervation to the costal pleura.

11. Why may irritation of the central diaphragmatic pleura cause shoulder pain?
The central diaphragmatic pleura is supplied by the phrenic nerve, which can refer pain to the shoulder.

12. Why does visceral pleural irritation usually not cause direct pain?
The visceral pleura lacks pain-sensitive sensory innervation.

13. What is the pleural space?
The pleural space is the narrow potential space located between the visceral and parietal pleura.

14. Why is the pleural space called a potential space?
It is called a potential space because the two pleural surfaces normally remain closely opposed rather than widely separated.

15. Approximately how much pleural fluid is normally present in each hemithorax?
Approximately 8 mL of pleural fluid is normally present in each hemithorax.

16. What is the main function of normal pleural fluid?
Pleural fluid lubricates the pleural surfaces and reduces friction as the lungs expand and recoil.

17. Why do the right and left pleural spaces normally not communicate?
They are separated by the mediastinum.

18. What creates negative pressure within the pleural space?
Negative pleural pressure results from the lungs recoiling inward while the chest wall recoils outward.

19. How does negative intrapleural pressure support breathing?
It helps keep the lungs expanded against the chest wall and allows them to follow thoracic movement.

20. What happens to pleural pressure during inspiration?
Pleural pressure becomes more negative as the diaphragm contracts and the thoracic cavity expands.

21. Where is pleural pressure most negative in an upright person?
Pleural pressure is most negative near the apex of the lung.

22. Which pleural layer is primarily responsible for producing pleural fluid?
Capillaries in the parietal pleura are primarily responsible for producing pleural fluid.

23. How is pleural fluid normally removed?
Pleural fluid is removed through lymphatic stomata in the parietal pleura.

24. What causes a pleural effusion to develop?
A pleural effusion develops when fluid production exceeds lymphatic drainage or when fluid removal becomes impaired.

25. What is a pleural effusion?
A pleural effusion is an abnormal accumulation of fluid within the pleural space.

26. What is a transudative pleural effusion?
A transudative pleural effusion develops when systemic pressure or protein abnormalities cause fluid to enter the pleural space without primary pleural inflammation.

27. What is a common cause of transudative pleural effusion?
Congestive heart failure is one of the most common causes of transudative pleural effusion.

28. How can congestive heart failure cause pleural fluid accumulation?
Increased pulmonary and systemic venous pressures promote fluid movement into the pleural space and may reduce lymphatic drainage.

29. How does severe hypoalbuminemia contribute to pleural effusion?
Low plasma albumin reduces oncotic pressure, allowing fluid to leave the blood vessels and collect in tissues and the pleural space.

30. What is hepatic hydrothorax?
Hepatic hydrothorax is a pleural effusion caused by ascitic fluid moving through small diaphragmatic defects, usually into the right pleural space.

31. How can atelectasis contribute to a pleural effusion?
Atelectasis may create more negative pleural pressure, which can draw fluid into the pleural space.

32. What is an exudative pleural effusion?
An exudative pleural effusion results from inflammation, infection, injury, or malignancy involving the lung or pleura.

33. What is a parapneumonic effusion?
A parapneumonic effusion is a pleural effusion associated with pneumonia.

34. What is an empyema?
An empyema is an infected pleural collection that contains pus.

35. What is a hemothorax?
A hemothorax is an accumulation of blood within the pleural space.

36. What is a chylothorax?
A chylothorax is an accumulation of chyle, a fat-rich lymphatic fluid, in the pleural space.

37. What commonly causes a chylothorax?
A chylothorax commonly results from disruption or obstruction of the thoracic duct.

38. What is a malignant pleural effusion?
A malignant pleural effusion occurs when cancer directly involves the pleura or obstructs pleural lymphatic drainage.

39. How can a large pleural effusion impair ventilation?
It compresses the underlying lung and reduces the volume available for expansion.

40. Why can pleural effusion cause hypoxemia?
Compressed or poorly ventilated lung regions may continue to receive blood flow, producing ventilation-perfusion mismatch.

41. What percussion finding is expected over a pleural effusion?
Dullness to percussion is expected over a pleural effusion.

42. What happens to breath sounds over a pleural effusion?
Breath sounds are usually decreased or absent over the fluid-filled area.

43. What happens to tactile fremitus over a pleural effusion?
Tactile fremitus is usually decreased because fluid separates the lung from the chest wall.

44. What chest radiograph finding commonly suggests a pleural effusion?
Blunting of the costophrenic angle commonly suggests pleural fluid.

45. What is the meniscus sign?
The meniscus sign is a curved upper border of pleural fluid seen on an upright chest radiograph.

46. Why is thoracic ultrasound useful in pleural effusion?
It can detect small fluid collections, estimate their size, identify loculations, and guide thoracentesis.

47. When might computed tomography be useful in evaluating pleural disease?
It may be useful when pleural thickening, malignancy, trauma, loculated fluid, or infection is suspected.

48. What is thoracentesis?
Thoracentesis is the insertion of a needle or catheter into the pleural space to remove air or fluid.

49. Why may thoracentesis be performed diagnostically?
It may be used to obtain pleural fluid for laboratory testing and determine the cause of an effusion.

50. Why may thoracentesis be performed therapeutically?
It may be used to remove fluid that is causing dyspnea, hypoxemia, pain, or lung compression.

51. What laboratory measurements are commonly obtained from pleural fluid?
Pleural fluid is commonly tested for protein, lactate dehydrogenase, glucose, pH, cell counts, microorganisms, and malignant cells.

52. Why is a thoracentesis needle inserted just above the upper border of a rib?
The intercostal vein, artery, and nerve run along the lower border of each rib, so inserting above the rib reduces the risk of injury.

53. What is a common patient position for thoracentesis?
The patient is commonly seated upright and leaning forward over an over-bed table.

54. Why should the patient avoid coughing or moving during thoracentesis?
Movement or coughing can shift the needle and increase the risk of puncturing the lung or injuring nearby structures.

55. What is re-expansion pulmonary edema?
Re-expansion pulmonary edema is fluid accumulation in a lung that has been rapidly re-expanded after a large amount of pleural air or fluid is removed.

56. What signs after thoracentesis may suggest a pneumothorax?
New chest pain, dyspnea, hypoxemia, diminished breath sounds, or respiratory distress may suggest a pneumothorax.

57. What is a pneumothorax?
A pneumothorax is the presence of air within the pleural space.

58. How does a pneumothorax cause lung collapse?
Pleural air eliminates the normal negative-pressure relationship, allowing the lung to recoil inward away from the chest wall.

59. What are common causes of pneumothorax?
Common causes include trauma, rupture of a pulmonary bleb, mechanical ventilation, and invasive thoracic procedures.

60. What percussion note is expected over a pneumothorax?
Hyperresonance is expected because air has accumulated in the pleural space.

61. What chest radiograph finding is typical of pneumothorax?
A visible pleural line with no normal lung markings beyond it is typical of pneumothorax.

62. Why may subcutaneous emphysema occur with pneumothorax?
Air may escape from the pleural space or damaged lung into the soft tissues beneath the skin.

63. How may a pneumothorax affect chest movement?
The affected side usually expands less than the unaffected side.

64. How may pneumothorax affect mechanically ventilated patients?
It may suddenly decrease lung compliance and cause increases in peak and plateau pressures.

65. What may occur during pressure-controlled ventilation when a pneumothorax develops?
Delivered tidal volume may decrease because the lung becomes less compliant.

66. How may a small, stable pneumothorax be managed?
It may be managed with observation, supplemental oxygen, and close monitoring for enlargement.

67. When is chest tube drainage generally needed for pneumothorax?
It is generally needed when the pneumothorax is large, symptomatic, traumatic, persistent, or associated with mechanical ventilation.

68. What is a tension pneumothorax?
A tension pneumothorax occurs when air enters the pleural space and cannot escape, causing pressure to rise progressively.

69. How does tension pneumothorax reduce cardiac output?
Increasing intrathoracic pressure compresses the great vessels and reduces venous return to the heart.

70. In which direction does the mediastinum usually shift during tension pneumothorax?
It usually shifts away from the affected side.

71. Why is tension pneumothorax especially dangerous during positive-pressure ventilation?
Each ventilator breath may force additional air into the pleural space and rapidly increase pressure.

72. What vital-sign changes may occur with tension pneumothorax?
The patient may develop tachycardia, hypotension, severe hypoxemia, and rapid cardiovascular deterioration.

73. Should treatment of suspected tension pneumothorax wait for a chest radiograph?
No, treatment should not be delayed when an unstable patient has strong clinical signs of tension pneumothorax.

74. What is the purpose of emergency needle decompression?
It releases trapped pleural air and temporarily reduces pressure on the lung, heart, and great vessels.

75. Why is chest tube placement required after needle decompression?
Needle decompression is temporary, while a chest tube provides continuous drainage and definitive management.

76. What is the purpose of a chest tube?
A chest tube continuously removes air, blood, pus, or other fluid from the pleural space so the lung can re-expand.

77. Where is a chest tube for pneumothorax usually directed?
A chest tube used to remove air is generally directed toward the upper or anterosuperior chest because air rises.

78. Where is a chest tube for pleural fluid usually directed?
A chest tube used to remove fluid is generally directed toward a dependent posteroinferior region because fluid settles with gravity.

79. What are the three main components of a chest drainage system?
The three main components are the collection chamber, the water-seal chamber, and the suction-control mechanism.

80. What is the function of the collection chamber?
The collection chamber receives pleural drainage and allows its amount and appearance to be measured.

81. What is the function of the water-seal chamber?
The water-seal chamber allows air to leave the pleural space while preventing atmospheric air from flowing back into the patient.

82. What is tidaling in a chest drainage system?
Tidaling is the rise and fall of fluid in the water-seal chamber with breathing or the mechanical ventilator cycle.

83. What may cause absent tidaling in a chest drainage system?
Absent tidaling may indicate lung re-expansion, a kinked or obstructed tube, or incorrect system positioning.

84. What can continuous bubbling in the water-seal chamber indicate?
Continuous bubbling may indicate an active pleural air leak, bronchopleural fistula, loose connection, or leak in the drainage system.

85. What may intermittent bubbling in the water-seal chamber represent?
Intermittent bubbling may occur when pleural air leaves the chest during coughing or exhalation as a pneumothorax resolves.

86. Why must a chest drainage unit remain below chest level?
Keeping the system below chest level promotes gravity drainage and prevents fluid from flowing back into the pleural space.

87. Why should dependent loops be avoided in chest tube tubing?
Dependent loops can collect fluid, obstruct drainage, and interfere with pressure transmission.

88. Why should chest tubes not be routinely clamped?
Routine clamping may trap pleural air and cause a tension pneumothorax.

89. Why should chest tubes not be aggressively stripped?
Aggressive stripping may create excessive negative pressure and damage pleural tissue.

90. What should be done if chest tube drainage suddenly becomes heavily bloody?
The change should be reported immediately because it may indicate active bleeding.

91. What drainage appearance is commonly associated with chylothorax?
Chylothorax drainage is often white or milky because it contains fat-rich lymphatic fluid.

92. What drainage appearance is commonly associated with empyema?
Empyema drainage is often thick, cloudy, yellow, or green because it contains infected material and pus.

93. What drainage appearance is typical of an uncomplicated serous pleural effusion?
Uncomplicated pleural effusion fluid is often clear or straw-colored.

94. What is pleurodesis?
Pleurodesis is a procedure that causes the visceral and parietal pleura to adhere, eliminating the pleural space.

95. Why may pleurodesis be performed?
It may be performed to prevent recurrent pneumothorax or repeated malignant pleural effusion.

96. How does a pleural friction rub differ from rhonchi?
A pleural friction rub does not usually clear with coughing or suctioning, while rhonchi caused by airway secretions may improve.

97. What happens to the mediastinum with a very large pleural collection?
A large pleural collection may push the mediastinum, trachea, and heart away from the affected side.

98. How does mediastinal movement differ in severe atelectasis?
Severe atelectasis causes volume loss that may pull the mediastinum toward the affected side.

99. Why is the direction of mediastinal shift clinically important?
It helps distinguish space-occupying pleural conditions from disorders that cause major lung-volume loss.

100. What findings should be integrated when evaluating a suspected pleural disorder?
Assessment should integrate breath sounds, percussion, tactile fremitus, chest movement, imaging, oxygenation, ventilator data, and the patient’s clinical trend.

Final Thoughts

The pleura supports normal breathing by reducing friction, transmitting chest-wall movement, and maintaining the negative-pressure relationship that keeps the lungs expanded. Its visceral layer covers the lungs, while its parietal layer lines the chest wall, diaphragm, and mediastinum.

Pleural inflammation may cause sharp pain and a friction rub, while pleural air or fluid can compress the lungs and impair ventilation. Careful assessment of breath sounds, percussion, chest movement, imaging, oxygenation, and ventilator data helps identify these disorders.

Prompt thoracentesis, chest drainage, or emergency decompression may be necessary to restore lung expansion and prevent severe cardiopulmonary compromise.