Pleural Effusion

Question 1

What is a pleural effusion?

What is the difference between this, an empyema and haemothorax?

Answer 1

pleural effusion is the accumulation of fluid within the pleural space

empyema is a collection of pus within the pleural cavity

haemothorax is a collection of blood within the pleural cavity

Question 2

What does a clear, a yellow and a bloody pleural fluid sample tell you about the possible cause of illness?

Answer 2

Straw coloured / clear:

• transudate / exudate

Yellow / white , foul smelling:

• empyema / parapneumonic effusion

Blood:

• trauma, malignancy, pulmonary infarct

Question 3

What are the clinical features of pleural effusion?

Answer 3

• reduced chest expansion on affected side
• mediastinal displacement away from the affected side
• stony dull to percussion
• reduced or absent breath sounds
• reduced or absent vocal resonance

Question 4

Why are clinical features not always present in patients with a pleural effusion?

Answer 4

these will generally only be present when the effusion is greater than 500ml

Question 5

What size does an effusion need to be to be seen on chest X-ray?

Answer 5

an effusion of less than 300ml may not be seen on x-ray

an effusion of less than 500ml is unlikely to cause anything other than blunting of the costophrenic recess

>500ml will cause a clear fluid level

Question 6

What do you need to look for when trying to identify a pneumothorax on CXR?

Answer 6

look for the meniscus

this is likely to be a very long curve, perhaps rising all the way to the axilla

if the fluid level appears perfectly horizontal, it is likely to be due to co-existing pneumothorax

Question 7

If a pleural effusion is very large, what may it look like on CXR?

What can fluid below the lung be confused for?

Answer 7

if the effusion is large enough, the whole of one lung field may appear opaque

the mediastinum may be shifted to the opposite side

fluid below the lung can simulate a raised hemidiaphragm

Question 8

Where is a needle inserted when performing a diagnositic aspiration?

How much fluid should be taken?

Answer 8

• percuss the upper border of the effusion, then go 1-2 intercostal spaces below
• use 5-10ml of lideocaine and inject down to the pleura
• insert a 21G needle with syringe just above the ribs upper border (to avoid the neurovascular border)
• take 10-30ml of fluid

Question 9

Where should the fluid collected from diagnostic aspiration be sent?

Answer 9

• clinical biochemistry for presence fo glucose, protein, pH, amylase, LDH
• bacteria culture
• cytology
• immunology

Question 10

If diagnosis is not possible from fluid sampling, what should be done?

Answer 10

diagnosis may be possible with a pleural biopsy

this should be CT guided for the best results

Question 11

What should be looked for on bloods in a suspected pleural effusion?

Answer 11

• protein - to check for hypoalbuminaemia
• glucose - to compare to the pleural fluid sample
• LFTs
• U&Es - to check for renal failure

Question 12

What are exudates?

What is the protein content?

Answer 12

fluids that have left the circulatory system and gone into lesions or areas of inflammation

they are defined by having a protein content >35g/L

Question 13

What are the contents of an exudate like?

Answer 13

the composition varies, but it can include pretty much anything that is in blood

it will nearly always have water and dissolved solutes

it may also have WBCs, RBCs and platelets

exudates have a high protein content

Question 14

What are transudates?

What is the protein content?

Answer 14

transudates are caused by disturbances in oncotic pressure (i.e. increases in venous pressure), and not by inflammation

they are defined by a protein content of <25 g/L

Question 15

What is the composition of transudates like?

Answer 15

they typically have a lower protein content, and will contain fewer cells

the fluid typically only contains mononuclear cells, such as macrophages and lymphocytes

Question 16

What is the difference in the way in which a transudate and exudate is formed?

Answer 16

a transudate is caused by a high pressure forcing plasma and some blood products out of the blood across a membrane

an exudate is formed by the leaking of fluid from one space to another

Question 17

Why is glucose measured in suspected pleural effusion?

Answer 17

a low glucose content in relation to the patient’s current blood glucose indicates the presence of cells (possibly native or foreign) in the fluid

this can indicate the presence of infection

Question 18

Why is pH measured when diagnosing pleural effusion?

Answer 18

a pH of <7.2 suggests empyema (exudate)

Question 19

Why is amylase measured when diagnosing pleural effusion?

Answer 19

raised amylase may indicate carcinoma, pancreatic disease or an oesophageal rupture

Question 21

In practice, what is used to determine the difference between a transudate and an exudate?

Why can it be difficult to tell them apart?

Answer 21

transudates often appear more “clear” than exudates but it is difficult to tell them apart when protein is 25 - 35 g/L

Light’s criteria is used to differentiate them

Question 22

According to Light’s criteria, when is a fluid an exudate?

Answer 22

A fluid is an exudate if:

• [pleural protein : serum protein] > 0.5
• [pleural LDH : serum LDH] > 0.6
• pleural LDH > 200

Question 23

How is pleural effusion managed if there is clear evidence of a transudative cause?

Answer 23

!!! DO NOT DRAIN THE EFFUSION !!!

If there is clear evidence of a transudative cause, the underlying cause should be treated without draining the effusion

e.g. LVF, renal failure, hypoalbuminaemia

Question 24

If you are unsure about what is causing a pleural effusion, what procedure should be performed?

Answer 24

PLEURAL TAP (thoracocentesis)

this is not the same as a chest drain, which often stays in place for several days

this just aspirates a sample of fluid

this fluid is then sent for cytology, LDH, protein, pH, Gram stain and AFB testing

(AFB = acid fast bacilli - TB)

Question 25

What bloods should be sent at the same time as pleural tap?

Answer 25

• LDH
• glucose
• CRP and ESR
• albumin
• amylase

Question 26

If pleural effusion has an exudative cause, how is it treated?

Answer 26

• the underlying disorder needs to be treated
• the effusion should be drained as necessary

this may mean draining the effusion many times

Question 27

Why does fluid need to be removed from a pleural effusion slowly?

Answer 27

large, fast fluid changes can lead to pulmonary oedema

maximum of 2L can be removed every 24 hours

Question 28

What methods can be used to remove fluid from a pleural effusion?

Answer 28

needle aspiration (same method as diagnosis) or chest drain

aspiration is typically used for empyema and haemothorax

no more than 1L should be drained at a time using this method

Question 29

What treatment is considered for draining a pleural effusion in malignancy and why?

Answer 29

pleurodesis or long-term in-dwelling chest drain

this is because most cases will recur within one month

pleurectomy may be used in some circumstances

Question 30

What is pleurodesis?

Answer 30

the pleural space is removed and the 2 layers of pleura are stuck together, either chemically or surgically

this prevents the accumulation of fluid

chemical pleurodesis is useful in cases of recurrent pleural effusion

Question 31

What agents are used in chemical pleurodesis?

Answer 31

• tetracycline
• talc
• bleomycin

pleurodesis talc is most useful in effusions caused by malignancy