Thoracentesis

Partly covered in the module: Medical Fundamentals >Body >Criticaltrauma patients (see THORACIC TRAUMA ).

Link to 'Skills': (Needle Thoracocentesis)

The pleural space is defined as a ‘potential’ space between the visceral pleura, which is adherent to the lung, and the parietal pleura, which is adherent to the chest wall (Pfenninger JL, Fowler GC (eds), 2003) , (Mathur PN, 2002) . Normally, the pleural surfaces are lined by a thin film of lubricating fluid, and intrapleural pressure is negative to that of atmospheric pressure. When the pleural space becomes filled with air (‘pneumothorax’) or extra fluid (‘pleural effusion’), the lung becomes compressed and the work of breathing increases (Pfenninger JL, Fowler GC (eds), 2003) .Air or fluid can be removed from the pleural space by simple aspiration (‘thoracentesis’) or chest tube drainage (Mathur PN, 2002) . Clinical differentiation between pneumothorax and pleural effusion is summarised in Tab. 1.

Thoracentesis (also known as ‘pleural tap’) is an invasive procedure, first described in 1852, to remove air or fluid from the pleural space for diagnostic or therapeutic purposes.
Spontaneous pneumothorax occurs in patients without a history of any event known to cause pneumothorax (e.g. trauma or physician intervention). It is nearly always caused by rupture of an apical bleb (bulla) during strenuous exertion, coughing, or air travel. Up to 80% of patients are tall young adults, more commonly smokers; male to female ratio is 6:1 (Doherty GM, Lowney JK, Mason JE, Reznik SI, Smith MA, editors, 2002) .

Evidence (according to the 2003 BTS guidelines) (Henry M, Arnold T, Harvey J, 2003)

• A lateral chest or lateral decubitus radiograph should be performed if the clinical suspicion of pneumothorax is high, but a PA chest X-ray is normal [Evidence level B].
• Observation should be the treatment of choice for small closed pneumothoraces without significant breathlessness [Evidence level B].
• Simple aspiration is recommended as first line treatment for all primary pneumothoraces requiring intervention [Evidence level A]
• Simple aspiration is less likely to succeed in secondary pneumothoraces and, in this situation, is only recommended as an initial treatment in small (<2 cm) pneumothoraces in minimally breathless patients under the age of 50 years [Evidence level B]
• Patients with secondary pneumothoraces treated successfully with simple aspiration should be admitted to hospital and observed for at least 24 hours before discharge [Evidence level C].
• Repeated aspiration is reasonable for primary pneumothorax when the first aspiration has been unsuccessful (i.e. patient still symptomatic) and a volume of <2.5 l has been aspirated on the first attempt [Evidence level B],
• Catheter aspiration of pneumothorax (CASP) can be used where the equipment and experience is available [Evidence level B].
• Catheter aspiration kits with an integral one way valve system may reduce the need for repeat aspiration [Evidence level C].
• If simple aspiration or catheter aspiration drainage of any pneumothorax is unsuccessful in controlling symptoms, then an intercostal tube should be inserted [Evidence level B].

It should be noted that iatrogenic pneumothorax may frequently occur after invasive thoracic procedures such as thoracentesis, transthoracic or transbronchial lung biopsy, pacemaker placement, and central venous access attempts (e.g. subclavian vein catheterization). Usually it is the result of inadvertent pleural injury during these procedures, therefore a post-procedure chest X-rays is mandatory in these cases (see Fig. 1) (Doherty GM, Lowney JK, Mason JE, Reznik SI, Smith MA, editors, 2002) .

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Fig. 1. Iatrogenic pneumothorax after thoracentesis for malignant pleural effusion (‘hydropneumothorax’)

Posteroanterior (PA) and latero-lateral chest X-ray examination: In the left pleural cavity, a large amount of fluid can be seen, producing an interface with the free air above it (double arrow). Pleural metastases can be detected as several arcuated and round, well-defined, soft tissue shadows on the pleura (arrows).[Courtesy of Prof. András Palkó, Department of Radiology, University of Szeged, Hungary].

Traumatic pneumothorax is generally caused by penetrating or non-penetrating (blunt) chest trauma (e.g. stab wound, rib fracture, bronchial rupture, esophageal injury). Sometimes it may be accompanied by free blood accumulation within the pleural space (‘haemopneumothorax’) (see Fig. 2). Prompt chest tube insertion should be performed to evacuate air and blood. Indications for operation (exploratory thoracotomy) include immediate drainage of more than 1500 ml blood after chest tube insertion or persistent bleeding >200 ml per hour (Doherty GM, Lowney JK, Mason JE, Reznik SI, Smith MA, editors, 2002) .

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Fig. 2. Haemopneumothorax as a result of the two ribs’ fractures

Anteroposterior (A-P) chest X-ray examination: Fractures are visible on the posterior and lateral segment of the 7th and 8th left ribs. Small amount of fluid and a total collapse of the left lung can be observed in the left hemithorax (‘hemopneumothorax’) (arrows).
[Courtesy of Prof. András Palkó, Department of Radiology, University of Szeged, Hungary].

Immediate decompression by transthoracic inserting of a large-bore needle attached to a syringe, followed by prompt insertion of a chest tube, is indicated in cases of a tension pneumothorax. It may appear rapidly and, if untreated, may result in death. Tension pneumothorax is due to continued air entry into the pleural space under high pressures, which collapses the lung, shifts the mediastinum toward the contralateral side (see Fig. 3), and even can compress the uninvolved lung. This unusual situation may occur following rupture of an apical bleb if the visceral pleura tear forms a ‘flap’ (i.e. opening with inspiration and closing with expiration) (Bordow RA, Moser KM (eds), 1991) .

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Fig. 3. Tension pneumothorax

Posteroanterior (PA) chest radiograph: The right lung is totally collapsed (arrow) and the mediastinum is slightly shifted to the left. [Courtesy of Prof. András Palkó, Department of Radiology, University of Szeged, Hungary].

Evidence (according to the 2003 BTS guidelines) (Henry M, Arnold T, Harvey J, 2003)

If tension pneumothorax is present, a cannula of adequate length should be promptly inserted into the 2^nd intercostal space in the mid-clavicular line and left in place until a functioning intercostal tube can be positioned [Evidence level B].

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Fig. 4. Large pleural effusion

PA chest X-ray examination: The transparency of the left hemithorax is homogenously increased; the middle shadow is shifted to the right. [Courtesy of Prof. András Palkó, Department of Radiology, University of Szeged, Hungary].

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Fig. 5. Pleural effusion on chest X-ray in two views

1.PA chest X-ray examination: The right hemidiaphragm is elevated; its contour is sharp and arcuated as a result of the pleural fluid collection (arrow). 2.Friemann-Dahl's left recumbent view chest X-ray examination: Sharply-defined shadow of a free fluid collection can be seen in the right pleural cavity (arrows).[Courtesy of Prof. András Palkó, Department of Radiology, University of Szeged, Hungary].


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Fig. 6. CT examination of a hydropneumothorax

Unenhanced, axial scan: On the right dorsally more, on the left less pleural fluid is visualized (arrows). On the right ventrally pneumothorax is also visible (double arrow). [Courtesy of Prof. András Palkó, Department of Radiology, University of Szeged, Hungary].

Since many diseases produce a pleural effusion, sampling this fluid can help determine the diagnosis (Pfenninger JL, Fowler GC (eds), 2003) .In more than 90% of cases, analysis of pleural fluid yields clinically useful information. A transudate is defined as:

• pleural fluid to serum total protein ratio of less than 0.5,
• pleural fluid to serum lactate dehydrogenase (LDH) ratio <0.6,
• absolute pleural fluid LDH <200 UI or <2/3 of the normal serum level.
An exudate is any pleural fluid that does not meet the criteria listed above. On the other hand, patients may gain relief of their cardiopulmonary symptoms by removal of air or fluid by thoracentesis.

Clinical scenario

Your patient is a young, otherwise healthy individual without previous radiographic evidence of lung disease. He has severe shortness of breath, absent breath sounds on the left, a falling blood pressure (now at 80/50), and a hyperresonance to percussion in the left chest. You suspect the spontaneous pneumothorax that can result from the rupture of a subpleural apical bleb.

Indications for thoracentesis

A. Diagnostic

• To determine the cause of any pleural effusion of unknown aetiology
• To obtain pleural fluid for diagnostic tests (e.g. for analysis and culture in patients with pre-existing pleural effusion who are thought to have an infection [pleuritis])

B. Therapeutic

• To relieve shortness of breath or discomfort from large pleural effusions
• Spontaneous pneumothorax (NB. a minimally symptomatic spontaneous pneumothorax of less than 20% may be observed) (Pfenninger JL, Fowler GC (eds), 2003)

When repeated therapeutic thoracentesis is needed to treat recurrent pleural effusions, chest tube placement and drainage with subsequent pleurosclerosis should be considered (Doherty GM, Lowney JK, Mason JE, Reznik SI, Smith MA, editors, 2002) .

Contraindications to thoracentesis

A. Absolute

• Uncooperative patient
• Uncorrected bleeding diathesis (i.e. coagulopathy or thrombocytopaenia), or patient undergoing anticoagulant therapy)
• Portal hypertension (producing pleural varices) (Chen H, Sonnenday CJ, Lillemoe KD (eds), 2000)

B. Relative

• When chest tube placement is more appropriate
• Infected skin or soft tissue at the intended site of puncture (e.g. thoracic wall cellulitis or abscess, burn, herpes zoster, etc.)
• Bullous disease (e.g. emphysema) at the site of needle insertion
• Use of positive end-expiratory pressure (PEEP) during mechanical ventilation of the patient
• Only one functioning lung in the patient (diminished respiratory reserve)

Complications

• Pneumothorax is the most common complication of thoracentesis; if significant (>10%) or increasing (>20%), it requires a tube thoracostomy and negative suction until the air leak seals (Chen H, Sonnenday CJ, Lillemoe KD (eds), 2000) , (Doherty GM, Lowney JK, Mason JE, Reznik SI, Smith MA, editors, 2002)
• Reexpansion pulmonary oedema occurs when a large amount of fluid is removed at one time; to minimize its occurrence, no more than 1.5-2.0 l should be removed at a time (Doherty GM, Lowney JK, Mason JE, Reznik SI, Smith MA, editors, 2002)
• Hypotension (low blood pressure due to a vasovagal response)
• Haemothorax
• Infection
• Injury to the intercostal neurovascular bundle; the risk is minimized if the needle is introduced directly over the superior edge of the rib
• Subcutaneous haematoma

A chest X-ray should be done after the procedure to detect these and other possible complications.

The most common causes of pleural effusions are: cancer, congestive heart failure, pneumonia, recent surgery, and tuberculosis (in countries where TB is common). Pleural effusions are generally categorized as transudative or exudative. This differentiation is based on microscopic, gross, and biochemical characteristics of pleural fluid (Doherty GM, Lowney JK, Mason JE, Reznik SI, Smith MA, editors, 2002) .As mentioned above, after either penetrating or blunt chest trauma haemothorax (free blood within the pleural space) may occur. Chest computer tomography (CT) is the best radiographic examination for determining the extent and character of the effusion (Fig. 6). Ultrasound is often useful in identifying and localizing pleural effusions for diagnostic or therapeutic drainage (Doherty GM, Lowney JK, Mason JE, Reznik SI, Smith MA, editors, 2002) .

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