Miscellaneous Fluids Flashcards
Cerebrospinal Fluid: source, function, flow, collection method
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
CSF appearance
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
*CSF Glucose
- 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)
*CSF Total Protein
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
CSF Immunoglobulins
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
CSF oligoclonal bands
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
CSF lactate
Raised in:
- bacterial meningitis
- raised WBCs
Normal in viral meningitis
Not commonly done as it has no added advantage over CSF glucose
CSF asialo-transferrin
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
Pleural fluid
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
Transudative vs Exudative causes of pleural effusion
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
Pleural fluid appearance
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
Pleural fluid biochemistry
Light’s Criteria – ANY ONE of the following = exudative fluid
- pleural fluid protein/serum protein >0.5
- pleural fluid LDH/serum LDH >0.6
- 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
Ascitic/Peritoneal Fluid causes
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)
Ascitic fluid appearance
Straw = CHF, cirrhosis
Blood stained = malignancy, haemorrhagic pancreatitis
Turbid, purulent = peritonitis
Chylous
Ascitic fluid biochemistry
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
