Diagnostic approach to lower respiratory tract disease in horses Flashcards
What are the main presenting signs indicating LRT disease?
- Cough
- Bilateral nasal discharge
- Tachypnoea
- Dyspnoea
What causes stimulation of irritant receptors in LRT disease?
- Foreign material
- Turbulent air
- Mucus
- Chemical irritant
How does stimulation of irritant receptors visibly affect breathing?
High velocity expiration
How does airway inflammation lead to bilateral nasal discharge?
Increased mucus production and altered mucus composition
Caudal head problems cause bilateral discharge
Why do tachypnoea and dyspnoea present as signs of LRT disease?
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
What needs to be thought about when considering respiratory issues in horses?
- 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
What questions must be asked when collecting the history of a horse with a LRT issue?
- Disease time course and features
- Herd or individual problem
- Age and use of horse
- Management and environment
- Coexisting problems
What can be observed from a distance when diagnostically approaching a horse with suspected LRT disease?
- 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?
Hypertrophy of which muscle can be used diagnostically in LRT disease?
External abdominal oblique
- indicates chronic respiratory disease
- ‘Heave line’
Abnormalities on inspiration are indicative of…?
Upper respiratory tract collapse
Abnormalities on expiration are indicative of?
Lower respiratory tract collapse
Where is the auscultation window on a horse to examine for LRT disease?
- Start at the base of the trachea
- Move to thorax
- Noise at the bifurcation of the trachea is the loudest
What are some examples of adventitious breath sounds?
Abnormal
- Crackles
- Wheezes
- Pleural rubs
- Cough
- Expiratory grunts/groans
Describe a wheeze
= 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
Give examples of factors that could cause a wheeze?
- Thickened wall – oedema / inflammation
- Intraluminal obstructions – e.g. mucus/foreign body
- Bronchospasm
- Extra luminal compression
Describe coarse crackles
- Bubbling mucus
- Inspiration or expiration
- Radiate widely
Describe fine crackles
- Popping open of collapsed small airways
- Most common: early inspiration
- Indicator of narrow, lower airways
Describe pleural friction rubs
- 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
What is the purpose of using a rebreathing bag during auscultation?
Rebreathes its own CO2 to make it breathe harder
– creates a temporary acidaemia
- Allows adventitious lung sounds to be heard
What does thoracic percussion allow identification of?
Air vs fluid
What laboratory tests can be carried out as further diagnostic tests for LRT disease?
- Blood sample
- Inflammatory profile
- Lactate (tissue hypoxia)
- Blood gas profile (hypoxaemia, hypercapnia)
- PCR
- Virus isolation
- Bacterial culture
What are some other diagnostic approaches to LRT disease?
- Nasopharyngeal swab
- Endoscopy and transendoscopic tracheal aspirate
- Percutaneous tracheal aspirate
- Bronchoalveolar lavage
- Thoracocentesis
- Imaging
- Lung biopsy
- LRT samples
What are the advantages and disadvantages of transendoscopic tracheal aspirate?
Advantages: - Easy - Non-invasive - Sample representative of whole lung Disadvantages: - Sample contaminated by nasopharyngeal flora and equipment - Specialist equipment required
What is a Transtracheal aspirate?
Puncture through the skin to obtain a sample
