Lecture 41- Lower respiratory tract dz 2

EIPH definition

Alveolo‑capillary membrane rupture during intense exercise; blood originates from pulmonary circulation (document quote: “Alveolo-capillary membrane rupture”)

Exercise pressures

Pulmonary artery pressure 20 → 90 mmHg; pleural pressure −5 → −60 mmHg → stress across membrane

EIPH risk factors

Pulmonary capillary hypertension, blood rheology, subatmospheric pleural pressure, extra/intra‑thoracic obstruction, IAD, coagulopathy, bronchial neovascularization, fibrosis, locomotor forces

EIPH epidemiology

Worldwide; affects horses running at high speed; prevalence increases with exercise intensity, breed, speed, age

EIPH pathophysiology

Capillary rupture → hemorrhage → inflammation → fibrosis → reduced lung compliance → angiogenesis → vascular remodeling → increased susceptibility

EIPH clinical signs

Often none; bilateral epistaxis; poor performance (must rule out other causes)

EIPH diagnosis—endoscopy

Perform 30–120 min post‑exercise (up to 7 days); graded 1–4 severity

EIPH diagnosis—cytology

TW/BALF more sensitive; RBCs & erythrophages (>1 week); hemosiderophages (>21 days)

EIPH diagnosis—radiographs

Limited; dorsocaudal opacification possible; evaluate for secondary pneumonia

EIPH differentials—hemorrhage

Pulmonary abscess, trauma, pneumonia, foreign body, neoplasia

EIPH differentials—epistaxis

Guttural pouch mycosis, progressive ethmoidal hematoma, thrombocytopenia, trauma, neoplasia

EIPH treatment goals

Reduce capillary stress; decrease inflammation/angiogenesis; reduce bleeding; maintain capillary integrity

EIPH treatment—reduce pulmonary pressure

Furosemide (permitted in US/Canada/Mexico; not Europe); enalapril; L‑NAME; sildenafil; pentoxifylline

Furosemide notes

Used in ~90% TB racehorses; multimillion‑dollar annual cost; mechanism unclear; improves performance

EIPH treatment—increase alveolar inspiratory pressure

Correct URT collapse; Flair strips; bronchodilators; corticosteroids; reduce dust

EIPH other treatments

Aminocaproic acid, vitamin K, aspirin, biflavinoids, vitamin C

EIPH prognosis

Severe episodes → poor performance; one episode increases risk of recurrence

Adult pneumonia categories

Airways: bacterial bronchitis, septic IAD; parenchyma: pneumonia; extension: bronchopneumonia, pleuropneumonia

Adult pneumonia etiology—Gram positive

β‑hemolytic strep, Strep. zooepidemicus, Staphylococcus spp., Rhodococcus

Adult pneumonia etiology—Gram negative

Pasteurella, Actinobacillus, Bordetella; enteric: Klebsiella, E. coli, Enterobacter, Salmonella

Adult pneumonia etiology—anaerobes

Bacteroides, Clostridium, Peptostreptococcus

Adult pneumonia epidemiology

Any age; younger racehorses; prolonged transport; anesthesia; URT surgery; recent viral disease; aspiration after choke

Adult pneumonia pathophysiology

Weakened defenses (stress, viral infection, malnutrition, dust, anesthesia, exercise) + massive bacterial load (dysphagia, esophageal obstruction, head elevation, transport)

Head position importance

Lowered head essential for mucociliary clearance; head restraint during transport predisposes to pneumonia (document quote: “Head restraint may be the single most predisposing factor…”)

Adult pneumonia progression

Inflammatory infiltration → epithelial/endothelial damage → debris/fibrin → exudative pleuropneumonia → fibropurulent → fibrin deposits → pleural peel

Adult pneumonia clinical signs

Exercise intolerance, cough, nasal discharge, fever, anorexia, depression, tachypnea/dyspnea, pleurodynia, sternal edema, muffled sounds, endotoxemia

Adult pneumonia diagnosis

CBC/chem (inflammation), endoscopy, TTW/BALF, ultrasound, radiographs, thoracocentesis, thoracoscopy

Adult pneumonia treatment—antimicrobials

Penicillin, gentamicin, metronidazole; broad‑spectrum based on culture; minimum 10 days or until resolution

Adult pneumonia treatment—ancillary

NSAIDs, hydration, nutrition, oxygenation

Adult pneumonia treatment—pleural drainage

Indications: respiratory distress, emphysematous fluid, fetid odor, sepsis; perform early before fibrin; ultrasound‑guided

Adult pneumonia complications

Phlebitis, thrombosis, diarrhea, pneumothorax, cellulitis, endotoxemia, laminitis, abscess

Adult pneumonia prognosis

90% survival; 60% return to athletic performance; poor prognosis for hemorrhagic necrotizing pneumonia

Rhodococcus equi etiology

Gram+ facultative intracellular; ubiquitous soil organism; intracellular survival; zoonotic for immunocompromised

Rhodococcus epidemiology

Foals <6 months; sporadic or endemic farms; environment & management critical

Rhodococcus pathophysiology

Infection in first days of life; inhalation primary; ingestion secondary; lung → swallowed sputum → intestinal replication → manure → inhalation; outcomes: regressors vs progressors

Rhodococcus clinical signs

Slowly progressive; mild fever/cough → lethargy, anorexia, tachypnea/dyspnea → acute distress/death; chronic suppurative bronchopneumonia; extensive abscessation; subclinical lesions detectable by U/S

Rhodococcus diagnosis—lab

Hyperfibrinogenemia, ↑SAA, neutrophilic leukocytosis; serology (Vap‑specific Ig)

Rhodococcus diagnosis—imaging

Radiographs: alveolar pattern, consolidation; U/S: irregularities, focal consolidation, extrapulmonary lesions

Rhodococcus diagnosis—TTW

PCR for VapA; culture/sensitivity; interpret with clinical signs + cytology + imaging

Rhodococcus treatment—antibiotics

Macrolides + rifampin: erythromycin, azithromycin, clarithromycin + rifampin; lipid‑soluble, intracellular penetration; prolonged half‑life; ↑PELF

Rhodococcus treatment—adverse effects

Diarrhea, hyperthermia, tachypnea; mares: enterocolitis (coprophagia → C. difficile)

Rhodococcus treatment—monitoring

Treat 3–8 weeks; monitor fibrinogen; resolution of imaging lesions

Rhodococcus prognosis

70–90% survival

Rhodococcus prevention—management

Ventilation, dust control, density, isolation; reduce pasture contamination

Rhodococcus prevention—screening

Visual exam, TPR 2×/week, hematology, fibrinogen, SAA, imaging (U/S, radiographs)

Rhodococcus prevention—HIP

Hyperimmune plasma 1 L <48h + 2–4 weeks

Rhodococcus prevention—Gallium

Iron mimic taken up by bacteria; experimental

Rhodococcus prevention—antimicrobials

Resistance concerns; >80% subclinical foals recover without treatment

Other foal pneumonia causes—neonates

Hematogenous infection/sepsis, descending infection, iatrogenic aspiration, in utero infection

Other foal pneumonia causes—older foals

Strep. zooepidemicus, R. equi, others

Foal interstitial pneumonia

Acute severe interstitial disease; sporadic; rapidly progressive; 1–6 months; ALI/ARDS form

Pneumocystis jiroveci

Rare opportunistic fungal pneumonia; immunodeficiency; SCID Arab foals; other breeds with concurrent infection