pleural effusion

Question 1

what tests can you do from pleural effusion aspirate?

Answer 1

cytology -analyse cell content
microbiology -C+S, acid-fast bacilli, TB culture, gram stain
biochemistry: glucose, protein/albumin, LDH (lactate) , pH

Question 2

what are light’s criteria for a pleural fluid exudate?

Answer 2

Pleural fluid : serum protein ratio > 0.5
Pleural fluid : serum LDH (lactate dehydrogenase) ratio > 0.6
Pleural fluid LDH > 2/3 the upper limit of normal serum LDH

Question 3

how much fluid must be present for a pleural effusion to be detected on CXR?

Answer 3

300ml

Question 4

what is the normal pH of pleural fluid?

Answer 4

7.6-7.64

Question 4

what is the diagnostic difference between transudate and exudate?

Answer 4

transudate -protein <30g/L (in patients with a normal serum protein level)
exudate -protein >30g/L

Question 5

what causes transudative pleural effusions?

Answer 5

(low protein)
factors that alter hydrostatic pressure, pleural permeability, and oncotic pressure:
congestive heart failure, liver cirrhosis, severe hypoalbuminaemia, nephrotic syndrome

Question 6

what causes exudative pleural effusions?

Answer 6

changes to local factors that influence the formation and absorption of pleural fluid:
malignancy
infection eg pneumonia, empyema
trauma
pulmonary infarction
PE

Question 7

what should be done if a patient is thought to have a transudative pleural effusion but the light criteria suggest an exudate?

Answer 7

serum-pleural fluid protein gradient should be examined

Question 8

what does frankly purulent pleural fluid cuggest?

Answer 8

empyema -anaerobic if has putrid odour

Question 9

what does milky pleural effusion liquid suggest and its causes?

Answer 9

chylothorax or pseudochylothorax (chyle =lipid rich lymph from digestive system). most often caused by lymphatic obstruction secondary to malignancy, chronic inflammation, or thoracic duct injury by trauma or a surgical procedure.

Question 10

what are the causes of bloody pleural effusions?

Answer 10

trauma -most common
TB
aortic dissection
ruptured AA
malignancy

Question 11

what features of pleural liquid indicate urinothorax?

Answer 11

straw coloured with distinct ammonia smell

Question 12

what are the causes of black pleural fluid?

Answer 12

aspergillus niger infection
malignant melanoma
haemorrhage and haemolysis associated with non small cell lung cancer

Question 13

what is the next investigation in pleural effusion once there’s no diagnosis from pleural aspirate?

Answer 13

contrast enhanced CT thorax