Approach to sampling

Question 1

What is a rebreathing bag and how can it be used to check lung function?

Answer 1

• 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!

Question 2

What must selection of further diagnostic tests be based on?

Answer 2

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

Question 3

What does arterial blood gas analysis test?

Answer 3

• Tests respiratory function
• Take blood gas sample and measure arterial concentrations of oxygen

Question 4

Which artery can you use to measure arterial blood gas analysis commonly?

Answer 4

transverse facial artery

Question 5

With arterial blood gas analysis, what levels of mmHg mean you have hhypoxia and hypercapnia?

Answer 5

• Hypoxia = PaO2 < 80 mmHg
• Hypercapnia = PaCO2 > 45 mmHg

Question 6

What is a nasopharyngeal swab suitable for?

Answer 6

• 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

Question 7

What is nasopharyngeal swabs useful for finding?

Answer 7

• 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

Question 8

How can you perform a guttural pouch aspirate or wash?

Answer 8

• 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

Question 9

What can be seen here?

What does this mean?

Answer 9

can see chondroid – if you see this, means horse has strangles!!! Almost exclusively strep equi equi virus

Question 10

Name some methods of respiratory sampling

Answer 10

• Endoscopically guided tracheal aspirate
• Percutaneous tracheal aspirate
• Bronchoalveolar lavage
• Pleural fluid
• Lung biopsy

Question 11

How can you perform a endoscopically guided tracheal aspirate?

Why is it not sterile?

Answer 11

• 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…

Question 12

What are the advantages of endoscopically guided tracheal aspirate?

Answer 12

• easy to perform
• non-invasive
• Might not even need sedation
• sample is representative of the whole lung

Question 13

What are the disadvantages of endoscopically guided tracheal aspirate?

Answer 13

• 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

Question 14

How much you interpret results of bacterial culture from an edoscopically guided tracheal aspirate?

Answer 14

• 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?

Question 15

How can you perform a transtracheal wash?

Answer 15

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

Question 16

What are some advantages of transtacheal aspirate?

Answer 16

• no pharyngeal contamination if procedure performed successfully
• no specialised equipment
• useful in young foals where standard endoscopes are too large

Question 17

What are some advantages of transtacheal aspirate?

Answer 17

• 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

Question 18

What can you do with a transtracheal wash sample?

Answer 18

• Can culture
• Syringe
• Culture media
• Cytology
• EDTA (purple top)
• Rule out pharyngeal contamination
• Dictiocaulis arnfieldi

Question 19

What are you looking for on tracheal cytology?

What is often normal?

Answer 19

• 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

Question 20

From a transtracheal wash.

What can be seen here?

Answer 20

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

Question 21

What is show here from a trans tracheal wash aspirate?

Answer 21

Ciliated columnar epithelial cells

If they lost cilia, might be thinking of viral diseases – but might be processing artefact as well

Question 22

From a trans tracheal aspirate sample - what can you see?

Diagnosis?

Answer 22

Healthy Neutrophils

• Pink stuff in background is mucus
• Healthy neutrophils
• Evidence of inflammation
• Consistent in horse with equine asthma

Question 23

What is wrong with these neutrophils?

Answer 23

Degenerate Neutrophils

Some macrophages in here with foamy cytoplasm as well

Question 24

How can you perform a blind bronchoalveolar lavage?

Answer 24

• 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

Question 25

How can you perform a bronchoalveolar lavage via endoscope?

Answer 25

* Sedate horse (detomidine and butorphanol) * Pass endoscope into trachea with neck extended * Infuse 20cc lidocaine in 40 cc saline * Wedge in bronchus * Infuse 100-300 cc warm saline via biopsy port * Can do BAL with endoscope as well, same technique – but you use a very expensive camera! * Advantage is that you can steer scope into different areas

Question 26

What are some advantages of bronchoalveolar lavage?

Answer 26

* sample obtained from the area of tract that is most likely to be affected by e.g.: * EIPH * COPD * narrow range of cell populations aids interpretation * equipment cheap and accessible therefore used in all large animal species

Question 27

What are some disadvantages of bronchoalveolar lavage?

Answer 27

* site may not be appropriate in animals with * localised pulmonary abscesses or pneumonias * It is not a sterile sample and therefore cannot culture it!

Question 28

What cells are normal and abnormal is their numbers are increased/decreased with a bronchoalveolar lavage?

Answer 28

* Normal differential * Normal: mostly macrophages and lymphocytes * alveolar macrophages - 40 - 60 % * lymphocytes - 40 - 60 % * neutrophils - \< 5 % * Increased with equine asthma, bacterial pneumonia * mast cells - \< 2 % * eosinophils - \< 1 % * \>5% neutrophils with Heaves, Viral resp dz, bacterial pneumonia (degenerate) * \>5% eosinophils with respiratory parasitism, idiopathic eosinophilic immune-mediated diseases, and very rarely with Heaves

Question 29

How can you perform a pleurocentesis and what can you do with the samples?

Answer 29

* Ideally with ultrasonographic guidance * Blunt teat canula * Avoid heart and colon * No fluid from a normal horse but every horse has a degree of pleura fluid and is a case of trying to find it * EDTA for cytology * Red top for Gram stain * Sterile container with transport medium for aerobic and anaerobic culture * Can do with blunt ended teat cannula, but if you have lots of fluid – wont go into the lung with lots of fluid as acts as a buffer!

Question 30

What is the pleurocentesis procedure?

Answer 30

* Clip 5cm square b/w 7th and 8th ribs on the L and 6th and 7th ribs on the R, between the shoulder and the elbow * Scrub * Lidocaine bleb * Aim for the front of the rib (avoid intercostal arteries, veins and nerves along the caudal edge of the rib), go off the front of a rib rather than off the back of a rib * 20g 1.5 inch needle to “walk off the front of the rib” * Can use ultrasound guided * Stab incision * Advance teat canula through chest wall, stop cock and 10cc syringe * Single skin suture

Question 31

What are the advantages of a lung biopsy?

Answer 31

* not frequently performed * used for identification of specific forms of pathology * e.g. good for: * interstitial pneumonia rather than disease of airways * Documenting neoplasia

Question 32

What are the disadvantages of a lung biopsy?

Answer 32

* very invasive * complications include * uncontrollable haemorrhage * Pneumothorax * Will get epistaxis