Investigations in neuro infections Flashcards
Key principles around LP counselling
Capcity
Written consent
Strict aseptic technique
How to counsel paitents about LP
Explain procedure
Describe likely benefits - diagnosis, therapeutic if raised ICP
List common and important risks
Common risks of LP
Back pain
Shooting pain down legs - sciatic
Localised bleeding
Rare risks of LP
<1% of time
Persistent headaches (low ICP), leaking , infefction, lower limb weakness
INdications for LP
Diagnostic - infection - meningitis/encephalitis, SA haemorrhage, MS, malignancy etc
Therapeutic - Reduce ICP
Spinal epidural - pain relief in labour, anaesthesia - lower limb surgery
What is risk if raised ICP and do LP
Brain stem herniation through foramen magnum
Indications for brain imaging before LP
Focal neurological signs
Papilloedema (blurred optic disc)
Continious or uncontrolled seizures
Reduced or fluctuating consciousness level
Cautions and CI for LP
Raised ICP signs - brain imaging first
Bleeding risk - deranged blood clotting or low platelet count, on anticoagulation (eg warfarin if INR>1.4)
Severe sepsis signs, evolving rash
Infection at site of LP
LP position
Knees and hips and neck flexed
Better to use US technique
What is the pro and cons of sitting position
Easier to find landmark
Cant measure opening pressure due to gravity (elevated)
Where insert needle for LP
Below ornic matularis (end of spinal cord)
L3-4
Also can use:
L2-L3
L4-L5
What would red cells >10 in CSF suggest
Traumatic tap or SAH
What does high neutrophils on LP suggest
Bacterial meningitis
What does high lymphocytes on LP suggest
Viral and TB meningitis or encephalits, inflammatory and malignant conditions
Normal opening LP pressure
8-20cm
Elevated from most problems
Nomrla protein, glucose, WCC and RBC in LP
RBC - <10
WCC - <5 cells
Protein - 0.15-0.45g/L
Glucose - 60-80%
When is protein high LP
Infection - TB> bacterial > viral
Inflam conditions
GBS
oligoclonal bands - MS
TB on LP
Lymphocytes
Low/v low glucose
Protein - high/v high
Gram positive vs gram negative colour
Gram + (peptidoglycan wall) -> dark purple eg sterp pneumoniae gram + cocci
Gram negative -> pink (safarin stain) N.meningitidis diplococci
What bacteria are most common cause of infective endocarditis
Streptococci
Gram stain technique
Primary stain - crystal violet 1 minute
2 - Mordant - gram iodine for 1 min
3 - water rinse
3 - decolourisation - acetone 2-3s or thyl alcohol 20-30s, water rinse
4 - counter stain safarin 30-60s, water rinse and blot
What colour are gram positive bacteria on stain
Purple
What colour are gram negative bacteria on stain
Pink
What gram is strep (what colour on stain)
Gram positive cocci - purple
Round or oval shaped
Strep pneumoniae appearance
Lancet shape in pairs
Enterococci appearnaec
Short chain
Oral viridians strep appearance
Long chains
Strep pyogenes appearance
Medium to long chains
How to differentiate strep and staph
Catalase test - scoop colony on small loop and dip in hydrogen peroxide
Staph bubbles - releases 02
Strep doesn’t
What see in alpha haemolytic strep agar plate
Partial haemoltysis - greenish dicoularation
What streps are alpha haemolytic
Pneumoniae (bile soluble, capsule, optochin sensitive)
Viridans- mutans, sanguis (oppostie to all brackets)
Oral
Beta haemolytic streptococcus appearance on agar
Complete haemolyiss - clear
What streps are Beta haemolytic
Pyogenes (group A), agalactiae (group B)
V pathogenic
Gamma haemolytic strep appearance on agar plate
Enterococcus
E.faecalis, e.faecium
Techniques used to identify bacterial specific species if complex infection
Mass spectometry
Panel of biochemical reactions (slower)
Method for susceptibility testing
Discs of filter paper impregnated with specific antibiotic concs on agar plate
zone of inhibition - whether effective - if has zone, susceptible
How find speciifc level of sensitivity to an antibiotic
E test for MIC - minimum inhibitory concentration
When use E test/MIC
Long course antibiotics for deep infections, endocarditis
How do strep appear on blood agar
Smooth white/grey colonies, catalase negative
Alpha, beta or non haemolytic
