Approach to LRT Disease in SA Flashcards
What is the structure of the mammalian airway?
•Airways of the mammalian lung consists of a branching tree of blind ending tubes.
This design creates physiological problems.
•Mammalian lung contains two types of airways:
- Conducting - carry air to and from respiratory airways.
- Respiratory - responsible for gaseous exchange with blood.
- ‘inverted’ tree – gaseous exchange at pulmonary parenchyma
- Disease gets worse when its higher up – e.g. worse to have a tracheal occlusion rather than part of an alveoli of the left lobe for example
- Cyanosis is difficult to generate with lung disease – if cyantoci with lung disease, a LOT of the lung is abnormal but can get quite cyanotic quite quickly with laryngeal disease
How do we approach animals with lower airway disease?
•Signalment (age, breed, sex, neuter status)
–Important for breed related disorders and helping to organise your differentials list
•Full and thorough clinical history
–Including:
- Diet, drinking, eating, urination, defecation, fluctuations in body weight
- Abnormal clinical signs at home/outside
- Any changes in activity level at home
- Any changes in personality / behaviour
- Changes in voice – laryngeal lesions – any change with bark or meow – rarely asked! If you don’t ask, you don’t know
- Facial deformity
How should I approach this LRT case in the consulting room?
•Observe the patient closely
–First critical aspect is whether the patient requires emergency admission or appears clinically stable – what are they doing at rest?
•A significant number animals with lower airway disease will be presented for acute deterioration
–Condition of patient
–Breathing character
•rate, pattern, regularity, depth and apparent effort
–Mucus membrane colour
- Pale, cyanotic, normal
- Some animals that are anaemic will look like they have resp disease to compensate for lower oxygen
- Behaviours that are worrying the owner
What breathing patterns are demonstrated?
- Normally inspiratory phase is longer than expiratory, in lower airway disease this is often reversed.
- Normal respiratory effort is minimal at rest
- Upper respiratory tract disease – slow respiratory rate and an exaggerated inspiratory effort (longer phase)
–Inspiratory effort increased
•Lower respiratory restrictive disease e.g. IPF, pleural effusion – fast shallow breaths
–Often both phases of breathing altered
–Interstitial fibrotic lung disease often limited to increased inspiratory effort – due to reduced lung compliance
•Pleural diseases – loss of pleural adhesion increases required effort to breathe.
–Inspiratory effort increased – lungs not stuck to body wall, so have to increase effort to expand the lungs
What is paradoxial respiration?
•Paradoxical respiration – respiratory muscle fatigue leading to opposing movements of the chest and abdominal wall. e.g. inspiration the caudal ribcage collapses inward and the abdominal contents are displaced caudally. Can occur in may cases of respiratory disease but is generally a poor sign.
–May get loss of syncope between chest and abdomen
Define:
- Tachypnoea
- Hyperpnoea
- Orthopnoea
- Trepopnoea
•Tachypnoea
–Increased respiratory rate
•Hyperpnoea
–Increased respiratory effort
•Orthopnoea
–Dyspnoea in any position other than standing or erect sitting – usually due to bilateral pulmonary oedema
–Abnormal breathing in a position
•Trepopnoea
–Postural abdnormalities on one side compared to other e.g. one lung may be abnormal e.g. a tumour, when they are lying in their cage after sedation for example – remember not to lie them on their good lung! Don’t put good lung underneath as they will struggle
–Dyspnoea in one lateral recumbency but not the other – unilateral lung or pleural disease, or unilateral airway obstruction e.g unilateral pleural effusion
- Often seen in patients when in hospitalised and in lateral recumbency
- Can be dramatic deterioration so always be vigilant for this
How do I approach a thoracic examination?
•Thoracic palpation
–Presence of - apex beat, rhonchi, masses, deformities, pain (e.g. rib fractures)
•Thoracic auscultation
–Hindered by purring, panting, growling!
–Use both sides of your stethoscope
•Normal sounds
–Inspiratory – soft, low pitched
–Expiratory – none or softer and lower pitched
–Listen to both phases and across the chest
What are crackles? What are the different types?
•Crackles – ‘sweet wrappers’ (rales) – Dry or moist
–moist – CHF and most prominent on inspiration (right hilar position 1st) – usually some resp distress. Moist crackles – low pitched, fine popping inspiratory sounds
–Dry – acute or chronic. Dry crackles – higher pitched inspiratory sounds
–All crackles usually discontinuous
What are wheezes and rhonchi and what is the difference between them?
•Wheezes (high pitched) and rhonchi (low pitched):
–narrowing of airway (bronchi/trachea)
–Can be inspiration or expiration but most commonly expiration
–Wheezes and rhonchi – usually secondary to bronchial narrowing.
–These may be high or low pitched, abnormalities as there is something going wrong in the lumen
–Most commonly heard on expiration
–
How do I examine the chest using percussion?
- Determine the density of a part by tapping the surface with a finger
- Best for larger dogs and cats
- Determine whether the tympanic sounds created by the chest wall are normal, increased or decreased
–e.g pleural effusion – dull below fluid line and normal above it
–There are many different causes of increased and decreased tympanic sounds on percussion
- Increased tympanic sounds – pneumothorax, feline asthma, emphysema
- Decreased tympanic sounds usually unilateral – diaphragmatic hernia, chest masses, unilateral pleural effusion
How do I investigate the patient with lower respiratory tract disease?
- History – is the animal coughing or having respiratory difficulty/changed character
- Clinical examination
- Routine haematology and biochemistry
–Specific blood tests - e.g. serum Pro-BNP concentration
–Blood gas evaluation
•Diagnostic imaging
–Thoracic radiographs, fluoroscopy, CT, Ultrasound, scintigraphy, MRI
- Tracheal washes/Bronchoscopy – will it help?
- Lung FNA/biopsies – bronchoscopy may not be useful for this!
- NB these are often older dogs with concurrent disease other tests as clinically indicated!
- Recovery – its when they come around that you need to know what needs to be done, part of thorough history and where its problems are
With lower respiratory, what laboratory testing should you have?
•Minimum database of biochemistry and haematology – to make sure of no limiting comorbidities
–Always of value in respiratory patients
–Determines if underlying systemic condition present/likely
- Anaemia
- Eosinophilia, neutrophilia
–Use of assays such as NT-ProBNP to determine between cardiac and respiratory causes of coughing
•Blood gas evaluation (arterial and venous)
–Enables determination of oxygenation, ventilation/perfusion mismatching and acid-base balance
–Handheld analysers available
–Hypoxaemia – PaO2 <80mmHg
–Equations for determining effective perfusion and oxygenation of blood in standard texts
–Caution as sample for PaO2 needs to be arterial and taken in the absence of air
When are thoracic radiographs useful for LRT disease?
•Thoracic radiographs
–Where thoracic disease is suspected thoracic radiographs (at least 2 views) should always be taken. If just looking for significant parenchymal disease, a L and DV may ne okay but if looking for mets then probably need 3 views.
–Radiographs should only be taken when the patient is stable enough to do so!
–Severely dyspnoeic patients should be stabilised prior to radiographs in all but extremely exceptional circumstances
–Can consider horizontal beam radiographs for patients too dyspnoeic to lay down
- Aids with fluid identification and free gas
- Radiation safety issues may preclude this approach
What advantages does thoracic CT have over radiographs?
- Increased sensitivity (high resolution CT: 300 micrometers)
- Spatial assessment of disease
- Value to differentiate pleural, extrapleural and mediastinal disease
What disadvantages does thoracic CT have?
- Unable to perform easily in conscious patient
- Increased costs and limited availability
What are some pros and cons of thoracic ultrasound for LRT disease?
–Good for looking for stuff that’s not airated
–Value for pleural disease, to identify poorly aerated lung (atelectasis, consolidation, torsion)
–No real value in normal lung tissue as US cannot pass through air
When is transthoracic FNA useful?
–Ultrasound guidance in patients with discrete lesions
–Can also use fluoroscopic or CT guidance
–Lesions >1cm ideally
What are some contraindications for transthoracic FNA for LRT disease?
- Pulmonary bullae or cysts
- Coagulopathies
- Pulmonary hypertension
–Increases pressure in the chest, could end up with nasty haemoarrhage
- Pre-existing pneumothorax
- Suspected infectious process
What are some potential complications with transthoracic FNA?
Pneumothorax, empyema, bleeding, implantation, seeding of neoplasia – be careful with transthoracic FNAs
