Thoracentesis

Thoracentesis (also known as thoracocentesis or pleural tap) is an invasive procedure to remove fluidor airfrom the pleural spacefor diagnostic or therapeutic purposes. A cannula, or hollow needle, is carefully introduced into the thorax, generally after administration of local anesthesia. The procedure was first described in 1852.

Indications

This procedure is indicated when unexplained fluid accumulates in the chest cavity outside the lung. In more than 90% of cases analysis of pleural fluid yields clinical useful information. If a large amount of fluid is present, then this procedure can also be used therapeutically to remove that fluid and improve patient comfort and lung function.

The most common causes of pleural effusions are cancer, congestive heart failure, pneumonia, and recent surgery. In countries where tuberculosisis common, this is also a common cause of pleural effusions.

When cardiopulmonary status is compromised (i.e. when the fluid or air has its repercussions on the function of heart and lungs), due to air (significant pneumothorax), fluid (pleural fluid) or blood(hemothorax) outside the lung, then this procedure is usually replaced with tube thoracostomy, the placement of a large tube in the pleural space.

Contraindications

An uncooperative patient or a coagulationdisorder that can not be corrected are absolute contraindications.

Relative contraindications are site of insertion has known bullous disease (e.g. emphysema), use of positive end-expiratory pressure(PEEP, see mechanical ventilation) and only one functioning lung(due to diminished reserve).

Complications

Major complications are pneumothorax(3-30%), hemopneumothorax, hemorrhage, hypotension (low blood pressure due to a vasovagal response) and reexpansion pulmonary edema.

Minor complications include a dry tap (no fluid return), subcutaneous hematomaor seroma, anxiety, dyspnea and cough (after removing large volume of fluid).

Interpretation of pleural fluidanalysis

Several diagnostic tools are available to determine the etiologyof pleural fluid.

Transudate versus exudate

First the fluid is either transudateor exudate.

A transudate is defined as total protein pleural fluid-serum ratio of 0.5, LDH pleural fluid-serum ratio < 0.6, absolute pleural fluid LDH < 200 IU or < 2/3 of the normal serum level.

An exudate is any pleural fluid that does not meet aforementioned criteria.

Exudate

• Infection
• Inflammation
• Malignancy
• Iatrogenic
• Connective tissue disease
• Endocrine disorders
• Lymphatic disorders vs Constrictive pericarditis

Transudate

• Congestive heart failure
• Nephrotic syndrome
• Hypoalbuminemia
• Cirrhosis
• Atelectasis
• Peritoneal dialysis
• Vena cava superior obstruction

Amylase

A high amylase level (twice the serum level or the absolute value is greater than 160 Somogy units) in the pleural fluid is indicative of either acute or chronic pancreatitis, pancreatic pseudocystthat has dissected or ruptured into the pleural space, canceror esophageal rupture.

Glucose

This is considered low if pleural fluid value is less than 50% of normal serum value. The differential diagnosisfor this is:

• rheumatoid effusion
• lupuseffusion
• bacterial empyema
• malignancy
• tuberculosis
• esophageal rupture (Boerhaave syndrome)

Triglyceride and cholesterol

Chylothorax(fluid from lymph vesselsleaking into the pleural cavity) may be identified by determining triglycerideand cholesterollevels, which are relatively high in lymph. A triglyceride level over 110 mg/dl and the presence of chylomicrons indicate a chylous effusion. The appearance is generally milky but can be serous.

The main cause for chylothorax is rupture of the thoracic duct, most frequently as a result of trauma or malignancy (such as lymphoma).

Cell count and differential

The number of white blood cellscan give an indication of infection. The specific subtypes can also give clues as to the type on infection. The amount of red blood cellsare an obvious sign of bleeding.

Cultures and stains

If the effusion is caused by infection, microbiological culturemay yield the infectious organism responsible for the infection, sometimes before other cultures (e.g. blood cultures and sputum cultures) become positive. A Gram stainmay give a rough indication of the causative organism. A Ziehl-Neelsen stainmay identify tuberculosisor other mycobacterial diseases.

Cytology

Cytologyis an important tool in identifying effusions due to malignancy. The most common causes for pleural fluid are lung cancer, metastasisfrom elsewhere and mesothelioma. The latter often presents with an effusion. Normal cytology results do not reliably rule out malignancy, but make the diagnosis more unlikely.

References

• Thoracentesisfrom THE MERCK MANUAL, Sec. 6, Ch. 65, Special Procedures
• Intensive Care Medicine by Irwin and Rippe
• The ICU Book by Marino
• Procedures and Techniques in Intensive Care Medicine by Irwin and Rippe
• Pulmonary - Critical Care Associates of East Texas

External links

• A photo gallery of thoracentesis showing the procedure step-by-step.

This article is licensed under the GNU Free Documentation License.
It uses material from the http://en.wikipedia.org/wiki/Thoracentesis Wikipedia article Thoracentesis.