Diagnostic approach to equine respiratory system

Question 1

What are the 3 categories of stimulants to irritant receptors?

Answer 1

*Physical
*Chemical
*Inflammation

Question 2

What are the Physical irritants?

Answer 2

*Foreign material
*Turbulent air
*Mucus

Question 3

What are the chemical irritants?

Answer 3

*Osmolarity
*Irritant

Question 4

What are the presenting signs of LRT disease?

Answer 4

1.Coughing
2.Bilateral nasal discharge
3. Tachypnoea / Dyspnoea

Question 5

what is the pathogenesis of bilateral nasal discharge?

Answer 5

1.Airway inflammation
2.Increase mucus production + Altered mucus composition
3.Mucopurulent bilateral nasal discharge

Question 6

What causes increased resp rate + effort?

Answer 6

1. Hypercapnia, Acidaemia + Hypoxaemia
2. Aortic, Carotid + medulla chemoreceptors triggered
   3.Respiratory centre in medulla activated

Question 7

What % of maximal oxygen consumption does a horse use at rest?

Answer 7

4%

Question 8

What history knowledge should you find out about the horse?

Answer 8

• Disease time course and features
• Herd or individual problem
• Age and use of horse
• Management and environment
• Coexisting problems

Question 9

What observations should you do to a horse from a distance regarding LRT?

Answer 9

• Posture (extended head and neck = severe respiratory distress)
• Abdominal effort
• Respiratory Rate
• Respiratory Depth –
• Pattern – biphasic?
• Hypertrophy of Ext. ab. oblique
  – ‘Heave line’

Question 10

What part of the respiratory tract is more likely to collapse on inspiration?

Answer 10

Upper respiratory tract

Question 11

What part of the respiratory tract is more likely to collapse on expiration?

Answer 11

Lower respiratory tract

Question 12

If doing a general clinical exam what should you examine?

Answer 12

• All systems
• Temp / Heart rate
• Ventral oedema?
• Guttural Pouches & Lymph nodes
  – enlargement, discharges
• Nares and Nasal Passages
  – airflow obstruction
  – discharges

Question 13

What happens during inspiration dysponea?

Answer 13

*Intercostals sucked in
*Wheezing sound
*Inwards pressure on tube of URT = collapse

Question 14

What is a normal breath sound in a horse?

Answer 14

= turbulent air in large (>2mm) airways
*Soft blowing sound
*Inspiration > expiration
*Faster air = louder
*Low frequency sounds travel best through normal lung

Question 15

Where should you auscultate a horse?

Answer 15

*Bottom of trachea
*Centre of chest - where sound should be loudest
*Then move around the thoracic cavity

Question 16

What are abnormal adventitious breath sounds?

Answer 16

1. Wheezes
2. Crackles
3. Pleural rubs
4. Cough
5. Expiratory Grunts/groans

Question 17

What is a wheeze?

Answer 17

Airway narrowing and vibration

Question 18

What causes a wheeze?

Answer 18

Thickened wall – oedema / inflammation
Intraluminal obstructions – e.g. mucus /foreign body
Bronchospasm
Extra luminal compression

Question 19

What are the 2 different types of crackles?

Answer 19

1. Coarse crackles
2. Fine crackles

Question 20

What causes a coarse crackle?

Answer 20

Bubbling mucus
Inspiration or expiration
Radiate widely

Question 21

What causes fine crackles?

Answer 21

Popping open of collapsed small
airways
Most common: early inspiration

Question 22

What causes pleural friction rubs?

Answer 22

• Inflamed parietal and visceral pleural membranes rubbing
  together

Question 23

What would you use for thoracic percussion?

Answer 23

*Pleximeter
*Plexor

Question 24

What are further tests you could take for the respiratory system?

Answer 24

• Laboratory and Clinical Pathology
• Nasopharyngeal swab
• Endoscopy and transendoscopic tracheal aspirate
• Percutaneous tracheal aspirate
• Bronchoalveolar lavage
• Thoracocentesis
• Imaging
  – Radiography
  – Ultrasonography
• Lung biopsy

Question 25

What are LRT samples you can take to test for disease?

Answer 25

1. Tracheal aspirate (TA) 2. Bronchoalveolar Lavage (BAL) 3. Thoracocentesis

Question 26

What are the advantages of transendoscopic tracheal aspirate?

Answer 26

* easy * non-invasive * sample representative of whole lung

Question 27

What are the disadvantages of transendoscopic tracheal aspirate?

Answer 27

* sample contaminated by nasopharyngeal flora and equipment * Specialist equipment required

Question 28

What are the advantages of transtracheal aspirate?

Answer 28

* no pharyngeal contamination * no specialised equipment * useful in young foals when endoscopes too large

Question 29

What are the disadvantages of transtracheal aspirate?

Answer 29

* Horse may cough catheter into pharynx and contaminate sample * invasive – cellulitis – subcutaneous emphysema

Question 30

What cells are abnormal and what is an abnormal neutrophil count with a tracheal aspirate sample?

Answer 30

– Abnormal = >20% neutrophils – Abnormal = Presence of mast cells, eosinophils

Question 31

What is bronchoalveolar lavage? What is it good/not so good for?

Answer 31

* Small area of distal airway lavaged with saline – best for diffuse lung disease * Good for cytology * Unsuitable for bacteriology

Question 32

What are the advantages of bronchoalveolar lavage?

Answer 32

* sample obtained from DISTAL airways = most commonly affected * Best correlation with pulmonary function and histopathology * equipment cheap and accessible (unless endoscopically obtained)

Question 33

What are the disadvantages of bronchoalveolar lavage?

Answer 33

* Site may not be appropriate in animals with – localised pulmonary abscesses or pneumonias (cranioventral lobes) * Pharyngeal contamination – Culture not useful * Invasive

Question 34

What is the best way to diagnose asthma?

Answer 34

BAL - bronchoalveolar lavage

Question 35

When would you use BronchoAlveolar Lavage / Tracheal Aspiration?

Answer 35

BAL: better correlation with: * Airway obstruction (pulmonary function testing) * Exercise induced hypoxaemia * Lung histopathology TA is most useful for * Bacteriology * Focal lung lesions e.g. Abscess/neoplasia * Tracheal inflammation