Clinical Evaluation of the Respiratory System
1. Learning Objectives:
- Understand and be able to correctly use terminology specific to respiratory system disease.
- Understand how auscultable lung sounds are generated, be able to describe abnormal lung sounds and understand their clinical significance.
- Understand indications for specialized diagnostic procedures used in respiratory system (imaging, endoscopy, transtracheal aspiration, bronchoalveolar lavage,and thoracocentesis) and what kinds of information can be obtained from each.
3.2. Potential for infectious disease or parasite exposure
- Other individuals of the same species on the premises, number and health status
- Other species on the premises, numbers and health status
- Recent travel
3.3. Previous and concurrent illness
- Course, therapy and response
- Medication being administered at present
4. Complaints Suggestive of Respiratory Disease
4.1. Cough: a forced expiratory effort to clear airways
- Indicates impairment of mucociliary clearance or excessive production of secretions
- General characteristics: Dry, moist, productive. Animals often swallow secretions, so cough usually appears non productive
- Pattern and frequency: Post exercise, during excitement, nocturnal
- Potential adverse effects of severe coughing:
- removal of mucous layer and less effective ciliary transport
- dissemination of infection
- emphysema, pneumothorax or exhaustion if prolonged or severe
- Usually initiated by irritation in the nasal passages (foreign body, mass lesion, allergic response)
4.3. Tachypnea: increased respiratory rate
- Hypercapnia or hypoxia.
- Sensitive indicator of respiratory disease.
- Normal resting rates:
- cattle: 15 - 35/min
- cat: 20 - 30/min
- horse: 12 - 20/min
- dog: 10 - 30/min
- sheep: 20/min
- Labored or difficult breathing. Manifestations include flared nostrils, increased rate or depth of respiration, abduction of elbows, abdominal effort during breathing, refusal to lie down
4.6. Audible abnormal breath sounds
Indicate air flow limitation:
- Stertor: audible pharyngeal or upper respiratory sounds
- Stridor: high pitched, generally inspiratory sounds
- These suggest partial obstruction (nasal passages, larynx, tracheal collapse)
4.8. Nasal discharge
- Unilateral or bilateral
- Often removed and swallowed by animals; depigmented skin ventral to the nares suggests chronic nasal discharge
- General characteristics: serous, mucoid, purulent, sanguinous
5. Emergency Situations Requiring Rapid Assessment and Action
5.1. Upper airway obstruction
- Apnea or choking, ventilation is prevented
- Intubate or establish a tracheostomy
6. Physical Examination
6.1. Systematic assessment of all systems is mandatory
- Respiratory signs may be secondary to disease in another system, and abnormalities in other systems may reveal occult respiratory disease
6.2. Pattern and frequency of resting respiration
- Rapid shallow respiration suggests restrictive disease or pain
- Accentuated expiratory effort suggests obstructive disease
6.3. Examination of the upper respiratory Tract
- Conformation and symmetry of head and muzzle
- Nasal passages: Mucous membrane color, nasal discharge, naso lacrimal duct patency
- Sinuses can be percussed in large animals
- Oral exam: Mucous membrane color, CRT, sublingual area, tonsil, hard palate
- Larynx and trachea: External palpation - assess the firmness of palpation that elicits a cough
- Lymph nodes: Intermandibular and retropharyngeal
6.4. Auscultation of the lungs
- Lung sound terminology is now standardized by the American Thoracic Society and American College of Chest Physicians
- Evaluate both resting and deep inspiration
- Normal lung sounds: Vibration of air in central airways (>2mm) transmitted through pulmonary parenchyma to the chest wall:
- bronchial sounds: generated in airways
- vesicular sounds: large airway sounds heard at the periphery after attenuation during transmission through aerated parenchyma
- Changes in sound transmission:
- consolidated areas: more efficient acoustical conduction
- hyperinflation: attenuation of normal airway sounds
- pleural effusion or pneumothorax: increased reflection of sound at the pleural surface
- Increased intensity of normal sounds:
- increased air velocity: increased ventilatory effort or narrowed airways with higher flow rates
- inspiratory sounds: extrathoracic airway obstruction
- expiratory sounds: partial collapse of intrathoracic airways characteristic of obstructive diseases
- Abnormal or adventitious sounds changes in sound production:
- discontinuous (<20 msec.): crackles (rales). Explosive equalization of pressure as atelectatic areas reopen. Excess secretions in airways, rupture of fluid films or bubbles
- continuous (>250 msec.): wheezes (rhonchi). Vibration of constricted airway walls or intraluminal mass. Low pitched continuous sounds associated with secretions in airways may change after coughing
- pleural friction rubs: sliding of inflamed pleural surfaces
- Clinical correlations of abnormal lung sounds:
- late inspiratory crackles: atelectasis and pulmonary edema
- expiratory wheezes: characteristic of obstructive airway disease
- Resonant sound obtained by tapping over inflated lung vs. dull sound obtained over tissue devoid of air:
- lung just beneath the chest wall (4 7 cm), large intrathoracic masses (> 2 3 cm) or pleural effusion can be delineated.
- Normal Lung Fields for Large Animal Species:
|Equine:||Tuber coxae||17th space|
|Tuber ischii||16 space|
|Pt. Shoulder||11 space|
|Bovine:||Tuber coxae||11th space|
|Ovine:||Tuber coxae||11th space|
7. Specialized Diagnostic Procedures: Macroscopic Level
- Structure of entire thorax (spine, ribs, sternum, heart, lungs mediastinum). Small animals: lateral and DV or VD; large animals: standing lateral only
- Evaluation of pulmonary parenchyma for opacities: vascular, bronchial, interstitial or alveolar
- Nasal passages and sinuses (xeroradiographs helpful here)
- Non-invasive imaging using high frequency, low intensity sound waves:
- sound waves are reflected at tissue interfaces of dissimilar density (acoustical impedance)
- aerated (normal) lung is not penetrated by sound waves, but collapsed or consolidated lung, masses, and fluid are
- Greatest advantage is evaluation of the pleural space and peripheral masses in lung parenchyma. Pleural fluid accumulation, pleural adhesions, guidance for pleural aspiration.
7.3. Nuclear imaging: lung scans
- Gamma emitting isotopes used to assess regional ventilation and perfusion
- Requires isolation facilities for radiopharmaceutical decay and sophisticated detection and imaging equipment
- Leukocyte scans: Focal radioactivity emitted as pre labeled leukocytes are localized in abscess after reinjection
- Non invasive but available only at referral centers
- Direct examination of the airways; sampling via aspiration or biopsy
- Small animal bronchoscopy requires general anesthesia and allows direct visualization of airway lesions, foreign bodies, mucosal edema, and mucous plugs:
- allows direct assessment of dynamic airway changes (ex. collapse)
- allows sample collection by BAl or biopsy, and foreign body or mucous plug removal
- direct culture of secretions or catheter brush samples
- Large animal bronchoscopy is usually performed standing with sedation, and allows direct visualization of the nasal passages, larynx and trachea
- Rhinoscopy is done with general anesthesia using an arthroscope in small animals. Nasal passages and sinuses can be examined and biopsied
8. Specialized Techniques: Microscopic Specimens
8.1. Transtracheal aspiration
- Introduction of sterile saline via tracheal puncture and aspiration of cells and secretions directly from the lower trachea and bronchi:
- minimally invasive procedure excellent for large animals
8.2. Bronchoalveolar lavage
- Threading a sterile catheter through the sterile endotracheal tube or endoscope to sample distal airway and alveolar cells and secretions:
- wedge catheter in small airway and lavage region distal
- requires short term light anesthesia and may induce hypoxemia
8.3. Sample analysis: not quantitative for cell number or protein, since fluid recovery is variable
- Sediment and smear for cytology (cytocentrifuge), smear and gram stain, aerobic and possibly anaerobic culture
- Normal constituents of sample: mucus, columnar epithelial cells, macrophages, rare PMN
- Mucopurulent inflammation: Increased mucous, abundant PMN, bacteria
- Non purulent inflammation: Macrophages, eosinophils (allergic or parasitic reaction)
- Neoplastic cells
- Direct aspiration of fluid from the pleural space for culture and cytology or for therapeutic drainage:
- diagnostic and therapeutic technique
- quantitative sample for cell number and protein content
- An indwelling therapeutic chest tube is inserted in similar fashion for chronic drainage or correction of pneumothorax
- Major complications: sepsis and pneumothorax
- Percutaneous, via bronchoscope, or from surgical thoracotomy
- Best used in diagnosis and prognosis of diffuse disease
9. Specialized Procedures: Functional Assessment
9.1. Blood gases
- Arterial blood sample in a sealed heparinized (glass or plastic) syringe for PaO2, PaCO2, pH, and [ HCO3 ]:
- equilibration with room air in bubbles or through the open syringe end must be prevented
- chill to slow metabolism of blood cells if not analyzed within 10 min.
- heparin is the only acceptable anticoagulant for blood gas samples
- PaCO2 is the most accurate evaluation of ventilation
- Evaluation of acid base status:
- respiratory acidosis: decreased pH and elevated PaCO2
- respiratory alkalosis: increased pH and depressed PaCO2
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