Miscellaneous Fluids

Question 1

Cerebrospinal Fluid: source, function, flow, collection method

Answer 1

Produced by choroid plexus (ultrafiltrate of plasma with intrathecal secretions added)

• protects brain from sudden change in pressure
• maintain stable chemical environment
• removes waste from cerebral metabolism

Flow: lateral ventricle –> via interventricular foramen to 3rd ventricle –> cerebral aqueduct –> 4th ventricle –> 2 lateral and 1 medial aperture –> subarachnoid space (brain/spinal cord) –> reabsorbed into venous blood of dural sinuses

Collection by lumbar puncture

• L3/L4 needle insertion
• first 1-3 ml discarded (traumatic tap with blood)
• 1-3 ml each for biochemical and microbiological analysis

Question 2

CSF appearance

Answer 2

Clear/colourless = normal

Blood stained = traumatic tap (may be very faint and not obvious) or recent SAH (very obvious high concentration of blood)
– traumatic tap will give falsely high protein levels and low glucose levels

Yellow (xanthochromic) = SAH>12 hrs ago or jaundiced patient

Turbid = WBC present, infection

Question 3

*CSF Glucose

Answer 3

• normal = similar to plasma glucose level; >60% (ultrafiltrate)
• some CSF disorders a/w <50% concentration of plasma level

Concurrent plasma glucose sample needed!

Causes of low glucose:

• bacterial meningitis (c.f. normal in viral meningitis)
• increased WBC
• infiltration of malignant cells

Tube used: Fluoride (grey)

Question 4

*CSF Total Protein

Answer 4

Normal <0.7g/L

Causes of high protein:

• infection (bacterial/TB meningitis)
• –> vascular permeability and blood flow increased to facilitate migration of neutrophils (also allows more LMW proteins to move into infected area)
• malignant infiltration
• chronic inflammatory conditions e.g. MS, GBS
• blockage of spinal canal
• traumatic tap

Question 5

CSF Immunoglobulins

Answer 5

Polyclonal (from plasma) – each at very low concentrations

Increased LOCAL production of IgG in CSF in MS and SSPE – but measurements have poor sensitivity and specificity so no longer used

Question 6

CSF oligoclonal bands

Answer 6

Electrophoresis
- presence of a few clones of Ig at high concentrations in CSF

Causes:

• increased CSF Ig production e.g. MS, SSPE, GBS
• systemic inflammatory process with generalised oligoclonal Ig production

Must be compared with SPE of patients –> now rarely done since MRI available to assess brain conditions

Question 7

CSF lactate

Answer 7

Raised in:

• bacterial meningitis
• raised WBCs

Normal in viral meningitis

Not commonly done as it has no added advantage over CSF glucose

Question 8

CSF asialo-transferrin

Answer 8

Desialylated form, found in CSF/aqueous and vitreous humour

• 15% of transferrin in CSF
• not in nasal discharge, tears or saliva

Used when:
- rhinorrhoea after head injury –> check whether it is CSF leaking through nose with base of skull fracture

Question 9

Pleural fluid

Answer 9

Originates from interstitial spaces of the lungs, the pleura and intrathoracic lymphatics
- accumulation when production > absorption

Transudative = low protein content; due to change in hydrostatic or oncotic pressures

Exudative = high protein content; due to increased capillary permeability

Question 10

Transudative vs Exudative causes of pleural effusion

Answer 10

Transudate

• increased hydrostatic –> CHF
• decreased oncotic –> cirrhosis, nephrotic syndrome, protein malabsorption, protein-losing enteropathy
• decreased drainage –> lymphatic obstruction

Exudate (pleural diseases)
- pneumonia, malignancy, vasculitis, pulmonary infarct

Question 11

Pleural fluid appearance

Answer 11

Straw colour = CHF

Blood-stained = malignancy, vasculitis

Turbid, purulent = bacterial infection

Chylous = lymphatic leakage or obstruction –> chylomicrons float to the top after standing at 4 degrees for 18 hrs

Question 12

Pleural fluid biochemistry

Answer 12

Light’s Criteria – ANY ONE of the following = exudative fluid

1. pleural fluid protein/serum protein >0.5
2. pleural fluid LDH/serum LDH >0.6
3. pleural fluid LDH >2/3 URL serum LDH

Lipids

• +ve = obstruction or damage to lymphatics leading to leakage of lymph rich in chylomicrons
• high TG

Adenosine deaminase: specific for TB

Question 13

Ascitic/Peritoneal Fluid causes

Answer 13

Excess fluid in the peritoneal cavity
- 75% due to ascites, 10% malignancy, 5% CHF, 10% others

Transudative:

• increased hydrostatic pressure e.g. cirrhosis with portal HT, CHF
• decreased oncotic pressure e.g. cirrhosis with hypoalbuminaemia, nephrotic syndrome, protein-losing enteropathy or malabsorption

Exudative:

• pancreatitis
• peritonitis (bacterial or TB)
• malignancy (local or disseminated carcinomatosis)

Question 14

Ascitic fluid appearance

Answer 14

Straw = CHF, cirrhosis

Blood stained = malignancy, haemorrhagic pancreatitis

Turbid, purulent = peritonitis

Chylous

Question 15

Ascitic fluid biochemistry

Answer 15

Proteins: >30g/L = exudate; <30 = transudate

Glucose – usually not done (not useful)

Amylase

• markedly raised in pancreatitis
• moderately raised in rupture of pseudocyst, perforated peptic ulcer

Lipids – measure TG content when suspect chylous ascites

Question 16

Serum-ascites albumin gradient (SAAG)

Answer 16

No light’s criteria for ascites

SAAG = serum albumin - ascitic fluid albumin
–> >11g/L = increased portal vein pressure

>11g/L = transudate -- cirrhosis, CHF, portal vein thrombosis
<11g/L = exudate -- peritonitis, pancreatitis, peritoneal cancers

Question 17

Bacterial vs Viral Meningitis

Answer 17

Bacterial

• CSF turbid
• CSF protein = >0.7g/L
• CSF glucose = <60% plasma
• CSF WBC = high; P>L
• microscopy = gram stain +ve

Viral

• CSF clear
• protein normal
• glucose normal
• WBC high; L>P
• microscopy = gram stain -ve

Question 18

General approach to miscellaneous fluids

Answer 18

ABCDMC

• appearance
• biochemistry
• cell count and differential
• microbiology (culture, stain, microscopy, serology)
• cytology