Diagnostic approach to lower respiratory tract disease in horses Flashcards

1
Q

What are the main presenting signs indicating LRT disease?

A
  • Cough
  • Bilateral nasal discharge
  • Tachypnoea
  • Dyspnoea
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2
Q

What causes stimulation of irritant receptors in LRT disease?

A
  • Foreign material
  • Turbulent air
  • Mucus
  • Chemical irritant
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3
Q

How does stimulation of irritant receptors visibly affect breathing?

A

High velocity expiration

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4
Q

How does airway inflammation lead to bilateral nasal discharge?

A

Increased mucus production and altered mucus composition

Caudal head problems cause bilateral discharge

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5
Q

Why do tachypnoea and dyspnoea present as signs of LRT disease?

A

Hypoventilation, ventilation-perfusion mismatch and impaired gas diffusion at the alveolus lead to hypercapnia, acidaemia and hypoxaemia

  • > leads to the aortic, carotid and medullary chemoreceptors to activate the respiratory centre in the medulla
  • > increased respiratory rate and effort
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6
Q

What needs to be thought about when considering respiratory issues in horses?

A
  • Horses are supreme athletes
  • They have a huge respiratory capacity so often don’t show abnormalities until a large proportion of the capacity has been affected
  • Signs of respiratory disease aren’t always apparent at rest
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7
Q

What questions must be asked when collecting the history of a horse with a LRT issue?

A
  • Disease time course and features
  • Herd or individual problem
  • Age and use of horse
  • Management and environment
  • Coexisting problems
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8
Q

What can be observed from a distance when diagnostically approaching a horse with suspected LRT disease?

A
  • Posture (extended head and neck severe respiratory distress)
  • Abdominal effort (a horse at rest hardly needs to use its abdomen compared to a dyspnoeic horse)
  • Respiratory Rate
  • Respiratory Depth
  • Pattern – biphasic?
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9
Q

Hypertrophy of which muscle can be used diagnostically in LRT disease?

A

External abdominal oblique

  • indicates chronic respiratory disease
  • ‘Heave line’
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10
Q

Abnormalities on inspiration are indicative of…?

A

Upper respiratory tract collapse

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11
Q

Abnormalities on expiration are indicative of?

A

Lower respiratory tract collapse

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12
Q

Where is the auscultation window on a horse to examine for LRT disease?

A
  • Start at the base of the trachea
  • Move to thorax
  • Noise at the bifurcation of the trachea is the loudest
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13
Q

What are some examples of adventitious breath sounds?

A

Abnormal

  • Crackles
  • Wheezes
  • Pleural rubs
  • Cough
  • Expiratory grunts/groans
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14
Q

Describe a wheeze

A

= Airway narrowing and vibration

  • High velocity air through a narrower space creates a wheeze
  • Polyphonic wheezes = more than one sound
  • Monophonic wheeze = single note coming from a single place
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15
Q

Give examples of factors that could cause a wheeze?

A
  • Thickened wall – oedema / inflammation
  • Intraluminal obstructions – e.g. mucus/foreign body
  • Bronchospasm
  • Extra luminal compression
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16
Q

Describe coarse crackles

A
  • Bubbling mucus
  • Inspiration or expiration
  • Radiate widely
17
Q

Describe fine crackles

A
  • Popping open of collapsed small airways
  • Most common: early inspiration
  • Indicator of narrow, lower airways
18
Q

Describe pleural friction rubs

A
  • Inflamed parietal and visceral pleural membranes rubbing together
  • Variable – fine crackles to sandpaper rubbing together
  • Usually insp. and exp. at same point in respiratory cycle
19
Q

What is the purpose of using a rebreathing bag during auscultation?

A

Rebreathes its own CO2 to make it breathe harder
– creates a temporary acidaemia
- Allows adventitious lung sounds to be heard

20
Q

What does thoracic percussion allow identification of?

A

Air vs fluid

21
Q

What laboratory tests can be carried out as further diagnostic tests for LRT disease?

A
  • Blood sample
  • Inflammatory profile
  • Lactate (tissue hypoxia)
  • Blood gas profile (hypoxaemia, hypercapnia)
  • PCR
  • Virus isolation
  • Bacterial culture
22
Q

What are some other diagnostic approaches to LRT disease?

A
  • Nasopharyngeal swab
  • Endoscopy and transendoscopic tracheal aspirate
  • Percutaneous tracheal aspirate
  • Bronchoalveolar lavage
  • Thoracocentesis
  • Imaging
  • Lung biopsy
  • LRT samples
23
Q

What are the advantages and disadvantages of transendoscopic tracheal aspirate?

A
Advantages: 
- Easy
- Non-invasive
- Sample representative of whole lung
Disadvantages:
- Sample contaminated  by nasopharyngeal  flora and equipment
- Specialist equipment  required
24
Q

What is a Transtracheal aspirate?

A

Puncture through the skin to obtain a sample

25
What are the advantages and disadvantages of a Transtracheal aspirate?
Advantages - no pharyngeal contamination - no specialised equipment - useful in young foals when endoscopes too large Disadvantages - Horse may cough catheter into pharynx and contaminate sample - Invasive
26
What can a sample from a transtracheal aspirate be analysed for?
- Differential cell counts - Mucus - Gram stain - Bacterial culture and sensitivity
27
What would be abnormal findings on analysis of a sample from a transtracheal aspirate?
More then 20% neutrophils | Any mast cells or eosinophils
28
A bronchiolar lavage is suitable for ... and unsuitable for...?
Suitable for cytology and unsuitable for bacteriology
29
When collecting a sample via bronchiolar lavage, what must be present in the sample to show its been done correctly?
Must get Foam (surfactant) on your sample to show you’ve gone into the terminal airways
30
What are the advantages and disadvantages of bronchiolar lavage?
Advantages - sample obtained from DISTAL airways = most commonly affected - Best correlation with pulmonary function and histopathology - equipment cheap and accessible Disadvantages: - Site may not be appropriate in animals with localised pulmonary abscesses or pneumonias - Pharyngeal contamination - Invasive
31
How does the lung surface appear on ultrasound?
Bright white line
32
When is thoracentesis indicated?
Indicated whenever there is a pleural effusion