Friday, 26 December 2014

Pleural Effusion

Pleural effusions are really common. Like a pneumothorax, the size of the effusion doesn't correlate well with the severity of the symptoms. There are two types of pleural effusions - transudate and exudate, and the management and cause of both differs. 

The annual incidence of pleural effusion in the developed world has been estimated at 320 per 100,000 population per year.

Pleural fluid is produced by filtering from systemic capillaries within the parietal interstitium and production is greatest at the lung apex. Approx 0.13 mls/kg bodyweight of pleural fluid lubricates the space between the parietal and visceral pleura.

Pleural fluid is absorbed and drained via parietal lymphatic vessels. Normal pleural fluid is formed from the filtration of plasma by healthy parietal pleural membranes and has the following characteristics:
- a glucose content similar to plasma
- low sodium content (1-2 g/dl)
- low white cell count (<1000 cells / mm3)
- low lactate dehydrogenase (LDH) level (<50% that of plasma)

Drug Causes
granulocyte colony stimulating factor (G-CSF)
Pneumotox Online is a useful website for identifying drug associations with various lung pathologies.

Clinical Features
As well as looking for features of the effusion, remember to look for features of other diseases that may cause the effusion too. 
- bronchial breathing may be heard due to consolidated lung above the level of the effusion
- deviation of mediastinum and trachea to opposite side in large effusions

- Blunting of the costophrenic angle with effusions around 200ml
- 50ml on a lateral produces blunting
- fluid within the horizontal or oblique fissures
- eventually a meniscus will be seen
- mediastinal shift
- subpulmonic effusion (aka infrapulmonary effusion) may be seen when there is previously established pulmonary disease

Transudate vs Exudate
Unilateral effusion = think carefully - is it cancer??
Put a gas through the gas machine unless it's obviously pus.

Light's Criteria: exudate if ratio of fluid protein to serum protein is >0.5
ratio of fluid lactate dehydrogenase (LDH) to serum LDH is >0.6
fluid LDH is greater than two-thirds the upper limit of normal serum LDH

Management is normally based on treating the underlying cause. 

- 50% of patients with pneumonia develop an effusion and will resolve spontaneously. Empyemas need drainage, so you need to sample the effusion.  pH <7.2 = empyema. 

- Malignant effusions - cytology diagnostic in 60% of cases. Lung and breast cancer account for 50 - 65% of metastases, and ovarian and gastric cancer account for the rest. 

Only aspirate if symptomatic, Aspirations normally suffice and a chest drain is rarely needed but if a drain is placed in the ED, leave it in so that pleurodesis can happen through it. 
- Never drain more than 1.5 L at once - may get expansion pulmonary oedema or haemodynamic instability.  
- The triangle of safety is marked here. It is bordered by:
The anterior border of latissimus dorsi
The lateral border of pectoralis major
The superior border of the 6th rib


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