Next Lesson - Lung Cancer
Core
The pleural space is defined as the potential space between the visceral and parietal pleura (the visceral pleura covers the lung and the parietal pleura lines the chest wall). It is called a potential space because the two layers normally lie almost touching. The space holds only a tiny amount of fluid. Its pressure is normally negative, which means lower than atmospheric pressure, because the lungs recoil inwards while the chest wall pulls outwards. A pneumothorax is defined as the presence of air in the pleural space.
Pneumothoraces can be grouped by their aetiology (cause):
A primary spontaneous pneumothorax is, as the name suggests, a pneumothorax that occurs seemingly spontaneously, and not due to any underlying pulmonary pathology. Primary spontaneous pneumothoraces most commonly occur in young, tall, thin males, with no predisposing lung disease or history of trauma. It isn’t fully understood how primary spontaneous pneumothoraces occur. The most common line of thinking is that some people have small blebs (bubble-like structures) on the lung surface that can rupture. What triggers the rupture is unclear, and effort does not seem to be the cause. In one study of 219 people with a first spontaneous pneumothorax, more than 87% had been inactive when the symptoms began. Smoking greatly increases the risk. In one Swedish study, smoking raised the risk of a first spontaneous pneumothorax about ninefold in women and 22-fold in men. These figures are relative risks: how many times more likely a first spontaneous pneumothorax is, compared with people who do not smoke.
A secondary spontaneous pneumothorax occurs spontaneously as a consequence of underlying lung pathology. This is due to underlying conditions such as COPD (chronic obstructive pulmonary disease), asthma, cystic fibrosis (an inherited condition that makes lung mucus thick and sticky) or interstitial lung disease (scarring of the lung tissue). Pneumothoraces caused by trauma (for example a fractured rib or blunt chest trauma) are classified separately from primary and secondary spontaneous ones. So are iatrogenic pneumothoraces, which are caused by a medical procedure or treatment. An example is a pneumothorax after central venous line insertion (a long drip placed in a large vein in the neck, chest or groin).
A tension pneumothorax occurs when a one-way valve system is created at the place where the pleural membrane has been breached. Air can enter the pleural space on inspiration, but can’t leave during expiration. This is because the change in pressure on expiration causes the newly created valve to close.
The trapped air causes an increase in intrapleural pressure (the pressure inside the pleural space), to the point where it exceeds atmospheric pressure, and starts to collapse the lung. This is a medical emergency because the rising intrapleural pressure severely compromises ventilation and venous return (the flow of blood back to the heart), leading to rapid cardiorespiratory collapse.
A person with a pneumothorax will typically present with a sudden onset of pleuritic chest pain, a cough and breathlessness. Pleuritic chest pain is pain that gets worse with deep breathing, sneezing or coughing.
On examination the patient may be dyspnoeic (short of breath) and tachycardic (with a fast heart rate), but some people with a pneumothorax have few symptoms or none. On the affected side there may be reduced chest movements, hyper-resonance (a hollow, drum-like note) on percussion and reduced breath sounds on auscultation. Low blood pressure (hypotension) raises the possibility of a tension pneumothorax rather than a simple one (see below), but a tension pneumothorax can be present before the blood pressure falls.
Additional signs and symptoms suggesting a tension pneumothorax include severe respiratory distress, tracheal deviation (the windpipe pushed to one side) away from the pneumothorax, fatigue, a raised JVP (jugular venous pressure, the pressure in the large neck veins) and hypotension. These need to be checked for in any case of suspected pneumothorax because a tension pneumothorax is a medical emergency. Tracheal deviation is an inconsistent finding and is often absent, so its absence does not rule out a tension pneumothorax.
Diagnosis of a pneumothorax is usually confirmed with a chest x-ray. This will show an area without lung markings (the fine branching lines of the blood vessels in the lung) where the lung is usually seen. A tension pneumothorax is a clinical diagnosis (made from the history and examination, not from tests) and should be treated immediately without waiting for imaging; chest x-ray findings such as tracheal deviation may be seen if imaging is obtained.
Image - A chest radiograph (x-ray) showing a left-sided pneumothorax, which can be seen by the absent lung markings in the left lung field (the part of the x-ray where the left lung is seen). The arrow points to the outer edge of the collapsed left lung
Public Domain Source by Mynameisderek [Public domain]
Management of a pneumothorax depends on the type, the symptoms, the size and how stable the patient is. Conservative management (observation alone, with oxygen therapy if needed) can be considered for an adult with a primary pneumothorax who has no symptoms or is only minimally symptomatic, whatever the size. Minimally symptomatic means no significant pain or breathlessness and no physiological compromise (the body’s vital signs are stable). These patients need follow-up, and a chest drain should be considered if the pneumothorax enlarges or symptoms develop. If conservative management is not suitable, the options are aspiration (drawing air out with a needle and syringe) or insertion of a chest drain (a tube placed through the chest wall to let air or fluid out). Chest drains are used mainly when there are high-risk features. These are a tension pneumothorax, significant hypoxia (a low blood oxygen level), a pneumothorax on both sides, underlying lung disease, age 50 or over with a significant smoking history, or blood in the pleural space (haemopneumothorax). The size of the pneumothorax no longer decides by itself whether to intervene. The size mainly shows whether it is safe to insert a needle or a drain. When a drain is needed, it is inserted through the triangle of safety. This is the safe area on the side of the chest wall, with the edge of pectoralis major (the large chest muscle) in front and the edge of latissimus dorsi (the broad muscle of the back) behind. The drain goes in directly above a rib, so that the nerve and blood vessels running below each rib are not damaged. A common site is the fifth intercostal space (the gap between two ribs) at the mid-axillary line (the vertical line down the side of the chest from the middle of the armpit).
In comparison, a tension pneumothorax is a medical emergency. It should be treated as soon as possible by inserting a wide-bore cannula into the pleural space (needle decompression) until a chest drain can be inserted.
The traditional site is the second intercostal space at the mid-clavicular line (the vertical line down from the middle of the collarbone). In a review that pooled the results of observational studies, decompression with a 5 cm cannula failed in about 38% of cases at this site, compared with about 13% at the fourth or fifth intercostal space on the anterior axillary line (the vertical line down from the front fold of the armpit). The authors concluded that the fourth or fifth intercostal space on the anterior axillary line has the lowest predicted failure rate, so check which site your local protocol uses. After major trauma, NICE advises open thoracostomy (a small cut made through the chest wall into the pleural space) followed by a chest drain, rather than needle decompression, where the expertise is available.
A pleural effusion is a collection of fluid in the pleural space. Fluid accumulates when its formation exceeds its clearance. There are two types of effusion. Transudates (watery, low-protein fluid) usually arise from systemic (whole-body) changes in hydrostatic pressure (the pressure pushing fluid out of vessels) or oncotic pressure (the protein pull that keeps fluid in). Exudates (protein-rich fluid) arise from local disease that increases permeability or impairs lymphatic drainage. The type depends on the cause and is confirmed by analysing the fluid (see Light’s criteria below), not by whether fluid forms too fast or drains too slowly.
Classify an effusion by measuring protein and LDH (lactate dehydrogenase, an enzyme released by damaged cells) in both the pleural fluid and the blood serum. Then apply Light’s criteria (listed below) and interpret the result alongside the patient’s history and examination. Light’s criteria can wrongly label a transudate as an exudate, especially in heart failure treated with diuretics (drugs that make the kidneys pass more urine). This is because diuretics can raise the protein and LDH in the pleural fluid.
A transudate often has relatively low protein, but a pleural-fluid protein concentration <30 g/L alone is not definitive. Common transudative causes include heart failure, with raised hydrostatic pressure, and nephrotic syndrome (a kidney condition in which protein is lost in the urine), with reduced plasma oncotic pressure. Cirrhosis (scarring of the liver) can also cause an effusion. The most widely accepted explanation for how cirrhosis causes an effusion is that ascitic fluid (fluid in the abdomen) passes through small defects in the diaphragm into the pleural space. The resulting effusion is called a hepatic hydrothorax.
An exudate usually contains more protein because of local inflammation, increased permeability or impaired lymphatic drainage. Causes include malignancy (cancer), infection and pulmonary embolism. Protein concentration alone is insufficient to classify an effusion reliably.
Light’s criteria classify pleural fluid as an exudate if any of the following apply:
- Pleural fluid protein to serum protein ratio > 0.5
- Pleural fluid LDH to serum LDH ratio > 0.6
- Pleural fluid LDH greater than two thirds of the upper limit of normal serum LDH
Bilateral effusions often have a systemic transudative cause, such as raised hydrostatic pressure in heart failure or reduced oncotic pressure in hypoalbuminaemia (low blood albumin). A unilateral effusion may suggest a local exudative process, but either type can be unilateral or bilateral. Whether the effusion is on one side or both is a clue, not a substitute for determining the cause and analysing the fluid when indicated.
Symptoms of pleural effusion usually come on gradually, and include breathlessness, chest pain, a cough and symptoms of the underlying cause.
On examination, there may be ‘stony dullness’ (a flat, solid note when the chest is tapped) on percussion, reduced breath sounds, reduced vocal resonance (the voice sounds quieter through the chest wall) over the effusion, and reduced lung expansion. In a large effusion there may also be tracheal deviation away from the site of the effusion. ‘Stony dullness’ is characteristic of an effusion, but it is not pathognomonic (a sign that proves the diagnosis by itself): pleural thickening can produce similar findings. Chest imaging, particularly ultrasound, confirms whether pleural fluid is present.
Pleural effusions can be imaged using a chest x-ray. It may show blunting (a sharp corner becoming rounded or filled in) of the costophrenic and cardiophrenic angles (the sharp corners where the diaphragm meets the ribs and the heart). It may also show a meniscal line (a curved upper edge to the fluid, higher at the sides) where the fluid ends. On an upright film, blunting of the costophrenic angle usually needs about 200 mL of fluid, so small effusions can be missed.
Ultrasound-guided fluid aspiration (drawing fluid out with a needle, using ultrasound to find a safe site) is advised for an undiagnosed one-sided effusion. The fluid is sent for tests such as cytology (examination of the cells), protein, LDH, glucose, pH and culture. These tests show whether the fluid is a transudate or an exudate and help to find the cause. Fluid can also be removed to relieve breathlessness (therapeutic aspiration), but unless the underlying cause is treated the effusion is likely to recur.
Large pleural effusions that cause symptoms can be drained. One way is therapeutic aspiration. In general, the British Thoracic Society (BTS) advises removing no more than 1.5 L in one attempt. It also advises stopping if chest tightness, pain, persistent cough or worsening breathlessness develop. These limits help to prevent re-expansion pulmonary oedema (fluid in the lung after it re-expands too quickly). A chest drain may be used in some cases, for example a small tube to drain pleural infection (infected fluid or pus in the pleural space). For recurrent malignant (cancer-related) effusions, two options can be offered. One is an indwelling pleural catheter (a thin tube left in place so that fluid can be drained at home). The other is talc pleurodesis (using talc to make the two pleural layers stick together). However, definitive management is through treating the underlying cause.
Image - A chest radiograph (x-ray) showing a right-sided pleural effusion. The cardiophrenic and costophrenic angles are completely lost, and a meniscus can be seen at the superior margin of the effusion
Creative commons source by Yale Rosen [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]
Edited by: Dr. Maddie Swannack
Reviewed by: Dr. Thomas Burnell and Dr. Marcus Judge
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