Approach to sampling Flashcards
What is a rebreathing bag and how can it be used to check lung function?
- Large garbage bag
- Rebreath air: build up CO2
- Drive resp. centers
- Deeper, more rapid breaths
- Rebreath until animal starts to become distressed
- CONTINUE to LISTEN!
- Resting horse using a tiny amount of its lung capacity – can go an gallop them or increase resp effort by putting bag over their nose for a minute – increases partial pressure of CO2, drives respiratory centre and when you tack back off they should take a big breath – if they panic, you know their lung function isn’t great!
What must selection of further diagnostic tests be based on?
Must be based on the diagnostic goals
- ruling in or out the specific diseases on the differential diagnosis list
- will the results of the test change what therapy or management you choose?
- specific advantages and disadvantages of each test
What does arterial blood gas analysis test?
- Tests respiratory function
- Take blood gas sample and measure arterial concentrations of oxygen
Which artery can you use to measure arterial blood gas analysis commonly?
transverse facial artery
With arterial blood gas analysis, what levels of mmHg mean you have hhypoxia and hypercapnia?
- Hypoxia = PaO2 < 80 mmHg
- Hypercapnia = PaCO2 > 45 mmHg
What is a nasopharyngeal swab suitable for?
- Only suitable for bacterial culture of specific organisms that are not normal commensals of the pharynx
- No point going to look for things that will already be there!
- e.g. Streptococcus equi equi
What is nasopharyngeal swabs useful for finding?
- Useful for URT viruses
- Influenza, herpes – during shedding phase of viral disease
- Requires virus transport medium to keep respiratory epithelial cells alive
- Virus isolation
- Will try to do for influenza – need transport medium, no point sticking swab in post and expecting virus to survive. But is just for PCR – doesn’t matter, just need a swab
- Virus detection by PCR
How can you perform a guttural pouch aspirate or wash?
- Endoscope within GP
- PE tubing via biopsy port
- Aspirate mucopurulent discharge
- Lavage both pouches and reaspirate fluid
- Or Collect fluid from nose (culture centrifuged pellet)??
- Note: GP has commensal organisms
- Relevant pathogen: Streptococcus equi serovar equi
- Culture
- PCR
What can be seen here?
What does this mean?
can see chondroid – if you see this, means horse has strangles!!! Almost exclusively strep equi equi virus
Name some methods of respiratory sampling
- Endoscopically guided tracheal aspirate
- Percutaneous tracheal aspirate
- Bronchoalveolar lavage
- Pleural fluid
- Lung biopsy
How can you perform a endoscopically guided tracheal aspirate?
Why is it not sterile?
- Position endoscope at thoracic inlet
- Advance catheter and insert 30 mls sterile (buffered) saline
- Withdraw sample
- Post-exercise?
- Most widely used technique for sampling the airway, can go down and see for yourself how much mucus, can get a visual assessment of how bad disease is
- However, have put scope up through pharynx – so technically not sterile…
What are the advantages of endoscopically guided tracheal aspirate?
- easy to perform
- non-invasive
- Might not even need sedation
- sample is representative of the whole lung
What are the disadvantages of endoscopically guided tracheal aspirate?
- sample is contaminated by pharygneal flora
- sample can be contaminated by equipment
- May culture things from wash bottle of scope or scope channels
- wide range in normal cell populations
- cells poorly preserved
How much you interpret results of bacterial culture from an edoscopically guided tracheal aspirate?
- Must interpret results of bacterial culture in light of cytological findings, anticipated organisms, purity and weight of culture
- If you grow a pathogen and there is no inflammation in the lung, this HAS to be contamination. If there IS inflammation but no bacteria in the cells, likely a contaminated and dealing with animal with an inflamed airway. Neutrophils will continue to phagocytose bugs in the sample whilst its in the post! So can be difficult to interpret these –are the pathogens that we are culturing genuine, are they commensals, is it contaminated?
How can you perform a transtracheal wash?
Stab incision
15 blade
- Bypass pharynx
- Catheter through tracheal rings and sample blindly
- Will be good if you don’t have a scope
- Scalpel, LA, stab incision
- Stabilize trachea
- Insert stylet/cannula between rings with bevel pointing down
- Was done in this foal as endoscope was too big to fit up this foals nose
- Remove stylet
- Feed catheter through cannula down trachea
- This catheter never touches anything other than plastic and lung… lungs aren’t sterile so when you withdraw the catheter, it still doesn’t touch skin and surrounding tissues
- Inject 60 ml sterile saline down catheter
- Aspirate saline and tracheal fluid
What are some advantages of transtacheal aspirate?
- no pharyngeal contamination if procedure performed successfully
- no specialised equipment
- useful in young foals where standard endoscopes are too large
What are some advantages of transtacheal aspirate?
- horse may cough catheter into pharynx and contaminate sample – so back to square 1, so could still get contamination – check there isn’t lots of squamous epithelial cells, if there is – wasted sample
- invasive
- cellulitis
- subcutaneous emphysema
What can you do with a transtracheal wash sample?
- Can culture
- Syringe
- Culture media
- Cytology
- EDTA (purple top)
- Rule out pharyngeal contamination
- Dictiocaulis arnfieldi
What are you looking for on tracheal cytology?
What is often normal?
- Fungi often normal
- Looking for neutrophils
- Degenerate
- intracellular bacteria
- Horses get these in airways with lots of different diseases. If eosinophils, more consistent with parasitic and not allergic (if cats have eosinophils, more likely allergic not parasitic)
- Gram stain and culture
From a transtracheal wash.
What can be seen here?
Bacterial Pneumonia TTW Gram + Cocci
Extraellular and lots of intracellular bacteria
Degenerate neutrophil
Evidence of bacterial pneumonia
Cell numbers don’t matter – reflection of how much saline gone in and got back, not interested in counts – just general observations
What is show here from a trans tracheal wash aspirate?
Ciliated columnar epithelial cells
If they lost cilia, might be thinking of viral diseases – but might be processing artefact as well
From a trans tracheal aspirate sample - what can you see?
Diagnosis?
Healthy Neutrophils
- Pink stuff in background is mucus
- Healthy neutrophils
- Evidence of inflammation
- Consistent in horse with equine asthma
What is wrong with these neutrophils?
Degenerate Neutrophils
Some macrophages in here with foamy cytoplasm as well
How can you perform a blind bronchoalveolar lavage?
- Pass tube into trachea with neck extended
- Infuse 20cc lidocaine in 40 cc saline
- Wedge in bronchus
- flush in 60 mls x 3(4)
- Pass until you cannot get any further and fill balloon up, isolated area of lung – infuse about 300ml of saline and then aspirate it back
- Re-aspirate, initially discard
- Collect after sample becomes foamy (surfactant)
•
- Recover 50-90%
- Should be foamy appearance
- Don’t want it to come out of the other nostril or into the mouth
