Introduction
Thoracentesis is a diagnostic / therapeutic strategy consisting in the partial removal or total removal of pleural fluid, accumulated in excess within the pleural cavity. For this purpose, thoracentesis is the procedure of choice for pleural effusion. However, for therapeutic purposes only, thoracentesis is also indicated for treating accumulations of air undermined in the pleural cavity (pneumothorax).
In this article we will shed light on two main topics: how to interpret the test results? What complications can a patient incur by undergoing thoracentesis?
Interpretation of results
As we know, the analysis of pleural fluid is a necessary diagnostic test to trace the cause that caused the condition.
All pleural fluid samples taken by thoracentesis must be labeled and sent to the analysis laboratory. The most useful tests to check the liquid taken are:
- Amylase: a high level of amylase in pleural fluid, taken by thoracentesis, is an indicator of acute or chronic pancreatitis, esophageal cancer or perforation of the esophagus
- Acid-fast stain differential staining: differential staining used to identify bacteria that do not decolor by acid-alcohol treatment
- Gram stain: offers a general indication of the pathogenic component involved in the infection
- Culture and antibiogram: useful for tracing the pathogen involved in the infection and evaluating its susceptibility to various types of antibiotics
- Cell count: the number of white blood cells can give a rough idea about the type of infection. The detection of red blood cells on the sample may be a light that is lit with ongoing bleeding
- Determination of triglycerides and cholesterol → high levels of triglycerides (> 110mg / dl), the presence of chylomicrons and a milky appearance of the liquid indicate a chylous effusion (chylothorax). Typical consequence of traumas or malignancies
- Cytological examination: important diagnostic tool useful for detecting the possible presence of malignant tumor cells in the pleural fluid taken by thoracentesis
- LDH, pH, specific weight, total proteins: useful tests to distinguish a transudate from an exudate
The investigation of the liquid taken by thoracentesis is aimed at distinguishing an exudate from a transudate: the differential diagnosis allows the identification of the cause that triggered the disorder in a shorter time.
Detection of a transudative pleural fluid is often an expression of cirrhosis, pulmonary embolism, hypoalbuminemia, obstruction of the superior vena cava, congestive heart failure, nephrotic syndrome. The pH of the transudative pleural fluid is generally between 7.4 and 7.55.
The exudate, dependent on an inflammatory process, can instead be due to rheumatoid arthritis, cancer, pulmonary embolism, hemorrhage, lupus erythematosus, infection, endocrine pathologies, pneumonia, Marfan syndrome, trauma and cancer.
The differential diagnosis between exudate and transudate is obtainable by measuring proteins and LDH in pleural fluid and serum.
Complications of thoracentesis
Thoracentesis must be performed by doctors and specialists who are very experienced in the field: in fact, the doctor's inexperience can weigh heavily on the final outcome of the test. The technique with which thoracentesis is performed should not be approximate: only an experienced and prepared medical staff can guarantee the success of the procedure, reducing the risk of complications.
To increase the margin of safety and success, thoracentesis should always be imaging-guided: this means that before proceeding, the patient must undergo thoracic screening tests.
TORACENTESI AND PNEUMOTORACE
Paradoxically, among the most common complications of thoracentesis the pneumothorax stands out, detected in 3-30% of patients undergoing this medical procedure. It has been observed that with the aid of ultrasounds, the risk of pneumothorax is reduced to a minimum (0-3%). According to these words, it is clear how important it is to subject the patient to similar tests BEFORE performing thoracentesis.
In the absence of penetrating thoracic trauma or bronchial pleural fistulas, the risk of developing pneumothorax following thoracentesis increases in three circumstances:
- Lung laceration using the needle used in thoracentesis: similar complications often occur when aspiration of pleural fluid is performed without imaging test
- Involuntary introduction of air through the needle / catheter used in thoracentesis: expression of inattention or inexperience of the doctor performing the procedure
- Inability of the lung to re-expand properly: a similar complication reflects the presence of a bronchial obstruction or a narrowing of the visceral pleural leaflet. If the lung fails to expand properly, it remains trapped inside. Consequently, an extreme negative pressure is established in the pleural cavity: pulmonary pressure variation can favor pulmonary edema.
Even in the presence of a simple suspicion of non-expandable lung, in a patient in whom complete drainage of excess pleural fluid is necessary, it is advisable to proceed with the THORACOTOMY.
TORACENTESI AND OTHER COMPLICATIONS
In addition to "simple" pneumothorax, haemopneumothorax, hemorrhage, pulmonary edema and hypotension are among the major complications of thoracentesis.
When a large quantity of pleural fluid is evacuated (> 1 liter), the lung undergoes a rapid pressure change: in similar circumstances, the patient runs the risk of pulmonary edema. However, the true incidence of this complication is not known after performing thoracentesis.
The hypotension following large volume withdrawals should be treated with the expansion of the intravascular volume.
Even the cough is a complication after the evacuation of large volumes of liquid; fortunately, cough is a self-limiting phenomenon.
The formation of a small hematoma associated with chest pain is another mild complication often reported by patients previously subjected to thoracentesis.
