Lecture 39- Evaluation of lower respiratory tract

Normal equine lung anatomy

Horses lack deep interlobar fissures and distinct lobes; left lung = cranial/caudal; right lung = cranial/intermediate/caudal

Right bronchus significance

More straight → right pulmonary disease more common (document quote: “R bronchus more straight > right pulmonary DZ”)

Airway branching

Trachea → main bronchi (5–6th ICS) → lobar → segmental → subsegmental → bronchioles

Normal lung histology

Terminal bronchioles 0.5–1 mm; alveoli ~250 μm; ciliated, goblet, basal, brush cells; particle deposition via impaction, sedimentation, diffusion

Mucociliary clearance

Mucins + antimicrobials + ciliary movement remove pathogens; surfactant supports innate immunity

Innate immune pathways

DAMPs/PAMPs → TLRs (1,2,3,4), RAGE → MyD88, MAPKs, NF‑κB → cytokines/chemokines

Adaptive immunity

Dendritic cells → CD4+ T cells → B cells; macrophages, eosinophils, granulocytes involved

Pulmonary circulation

Low pressure/resistance; gas exchange + nutrients

Bronchial circulation

Nutrient supply to lymphatics, vasculature, airway tissues

History components

Age/breed, environment, job, recent events, endemic diseases, trauma, vaccination, chief complaint, prior medical problems

Physical exam components

Inspection, palpation, percussion, auscultation

Inspection findings

Demeanor, posture, mental status, movement, deformities, nasal discharge, cough, respiratory effort, RR

Palpation/percussion targets

Nostrils (airflow/odor), sinuses, lymph nodes, larynx/pharynx, trachea/jugular, neck, chest

Auscultation technique

Quiet conditions; rebreathing bag; evaluate trachea, bronchi, lungs

Respiratory vocabulary

Eupnea (normal), dyspnea, tachypnea, hyperpnea, apnea, hyper/hypoventilation (PaCO₂ changes)

Nasal discharge descriptors

Uni/bilateral; serous, mucoid, purulent, epistaxis

Cough descriptors

Dry/moist, frequency, productive, hemoptysis

Mucous membrane descriptors

Cyanotic, injected, pale, icteric

Adventitious sounds

Wheezes, crackles

Dyspnea types

Inspiratory, expiratory, mixed

Diagnostic tools

Imaging, respiratory sampling, pulmonary function testing, blood work

Respiratory endoscopy indications

Visualization; determine additional exams; URT + LRT evaluation

Endoscopy—trachea

Assess conformation, sensitivity, mucus (inflammation indicator), mucus scoring (0–5)

Endoscopy—blood

Indicates recent hemorrhage; scoring based on amount/timing post‑exercise

Endoscopy—bronchi

Determine sampling side; septum thickness score (STS) for age/inflammation/edema

Pulmonary radiographs

Only laterals in adults; 4 films needed; difficult due to chest movement; expensive equipment

Radiograph indications

Infectious/non‑infectious LRT disease, pneumothorax, diaphragmatic hernia, others

Ultrasound findings

Pleural line, ribs, chest wall; detects pleural fluid, consolidation, comet tails

Other imaging

Cardiac ultrasound, thoracoscopy, pulmonary scintigraphy (advanced)

Respiratory sample collection types

Tracheal wash, BAL, thoracocentesis, pulmonary biopsy

Tracheal wash indications

Collect LRT secretions for culture + cytology

TW techniques

Trans‑endoscopic (fast, visualization, contamination risk); trans‑tracheal (sterile, cheap, no visualization)

TW materials

Sterile prep, needle/catheter kit, saline, syringes, EDTA + red top tubes, aerobic/anaerobic transport media

TW cytology

Epithelial cells, neutrophils, eosinophils, erythrophages/hemosiderophages; variable results based on rest/exercise

TW bacteriology interpretation

Evaluate cytology, colony count, bacterial type

Common pathogens

Strep. zooepidemicus, Actinobacillus equuli, Pasteurella spp., Mycoplasma spp., E. coli, Klebsiella, Strep. equi equi

Likely contaminants

Coagulase‑negative staph, alpha‑hemolytic strep, Pseudomonas, S. aureus, Bacillus, Proteus

TW virology

PCR for EHV‑1/2/4/5, influenza; clinical vs subclinical detection

BAL indications

Lower airway inflammation assessment; asthma; diffuse disease

BAL equipment

Endoscope (visualization, costly) or BAL tube (cheap, no visualization)

BAL technique

Sedation, local anesthetic, wedge balloon, instill 250–300 mL saline, recover via syringe/vacuum

BAL fluid assessment

Recovery volume; surfactant; mucus; hemorrhage; cytology

BAL cytology

Macrophages (~50%), lymphocytes (~50%), neutrophils <5%, eosinophils, mast cells, erythrophages/hemosiderophages

Thoracocentesis indications

Confirm pleural effusion; collect fluid for cytology/culture; treat effusion/hemothorax/pneumothorax

Normal pleural fluid

Straw‑colored, clear, odorless; <10 mL; protein <3 g/dL; cell count <10,000/uL

Septic pleural fluid indicators

>10,000 cells/uL, degenerate neutrophils, cloudy/fibrin clots, foul odor (anaerobic), protein >3 g/dL, glucose <40 mg/dL

Chylous effusion

Predominance of normal lymphocytes

Lymphosarcoma effusion

Abnormal lymphocytes

Pulmonary biopsy

Transthoracic or transbronchial; indicated for diffuse disease; contraindicated in hemorrhage, pneumothorax, infection, respiratory distress

Pulmonary function testing

Conventional, oscillometry, plethysmography, forced expiration, flowmetrics

Lung function test comparison

Conventional = low sensitivity; oscillometry = moderate‑high; forced maneuvers = high; flowmetrics = portable

Arterial blood gas

Sample mid‑neck or base of neck; heparinized syringe; anaerobic; cooling; PaO₂ 95–100 mmHg; PaCO₂ 40–45 mmHg

Exercise testing

Used to evaluate dynamic respiratory issues

Blood work

CBC, chemistry, serology

Best sample for culture (MCQ)

Tracheal lavage fluid (A)

Ease of auscultation (MCQ)

False (B)

Timing of endoscopy post‑exercise (MCQ)

True (A)

TW cytology for inflammation (MCQ)

True (A)