VETM5291 Pulmonary Parenchymal Diseases

Small Animal Pulmonary Parenchymal Diseases

• These are non-infectious diseases of the lungs.
• The lecturer is Meghan Fick, DVM, MS, DACVECC.
• The course is VETM5291 Spring 2025.

Brief Outline

• Brief review of clinical signs and physical exam for pulmonary parenchymal diseases.
• Diseases processes: Non-cardiogenic pulmonary edema (NCPE), Pulmonary hemorrhage, Pulmonary contusions.

Pulmonary Parenchyma

• Parenchyma is the functional part of an organ.
• Alveoli, pulmonary microvasculature, and interstitial tissues make up the lung parenchyma.
• Gas exchange occurs within the alveoli and pulmonary capillaries.

Clinical Signs

• Cough
• Exercise intolerance
• Tachypnea
• Excessive panting
• Increased respiratory effort (leading to respiratory distress.)

Physical Exam Findings

• Increased or decreased bronchovesicular sounds
• Crackles
• Cyanosis
• Inspiratory and/or expiratory effort

Helpful Information

• Clinical signs and some physical findings can mimic airway, pleural space, and mediastinal diseases
• Also, non-respiratory causes of tachypnea need consideration

Step 1: Patient Stabilization

• Oxygen is a critical first step
• Anxiolysis/sedation may also be necessary

Pulmonary Edema

• Edema is abnormal fluid accumulation in tissues.
• Fluid accumulates in the pulmonary interstitial space and alveoli.
• Edema is caused by problems with fluid flow across capillaries and changes in pressure, volume of flow, and capillary permeability.
• 3 classifications of pulmonary edema MOA: high pressure PE, increased permeability PE, and Mixed PE.

Pulmonary Edema MOA - 3 classifications

• High pressure PE*
• Cardiogenic PE (fluid therapy)
• Increased permeability PE*
• ARDS
• TRALI (Transfusion-related acute lung injury)
• Mixed PE*
• Negative pressure
• Neurogenic/electrocution

Pulmonary Edema - Underlying Pathology

• Cardiogenic:* Increase in pulmonary transcapillary pressure (with increased left atrial pressure.)
• Non-Cardiogenic:* Increased pulmonary transcapillary pressure (without increased left atrial pressure), increased vascular permeability and the combination of both.

Cardiogenic Pulmonary Edema

• Most common type in veterinary medicine.
• Generally develops gradually.
• Pathogenesis: Left-sided cardiac failure leads to increased left atrial (LA) pressures, increased venous pressures, increased pulmonary capillary pressures and fluid leaks from vessels into the pulmonary parenchyma.

Diagnosis

• Thoracic radiographs
• Echocardiogram
• CT scans
• Edema fluid protein levels
• How to distinguish between cardiogenic and non-cardiogenic pulmonary edema on thoracic radiographs.

Non-Cardiogenic Pulmonary Edema

• Acute respiratory distress syndrome (ARDS)
• Transfusion-related acute lung injury (TRALI)
• Negative pressure pulmonary edema (NPPE) or post-obstructive pulmonary edema (POPE).
• Neurogenic
• Electrocution

Acute Respiratory Distress Syndrome (ARDS)

• ARDS is a clinical syndrome characterized by severe hypoxemic respiratory failure, severe pulmonary edema due to increased capillary permeability secondary to local (pulmonary) or systemic (extrapulmonary) inflammatory process.
• Causes include:
• Pulmonary:* aspiration pneumonia, pneumonia, pulmonary contusions, chest trauma, mechanical ventilation
• Extra-Pulmonary:* sepsis, systemic inflammatory response syndrome (SIRS), shock, pancreatitis, trauma, acute kidney injury (AKI)

Pathophysiology of ARDS

• Injury to the lungs (local or systemic)
• Acute exudative phase: fluid, proteins, red blood cells (RBCs), and white blood cells (WBCs) leak into alveoli, activating the immune system further
• Fibroproliferative phase: Type II pneumocytes proliferate, leading to interstitial fibrosis

Diagnostic Criteria for ARDS

• Acute onset (< 72 hours)
• Known risk factors
• Thoracic radiographs (bilateral, diffuse pulmonary infiltrates)
• High protein edema fluid
• Evidence of insufficient gas exchange on blood gas analysis

Treatment & Prognosis for ARDS

• Oxygen therapy (often requiring mechanical ventilation)
• No evidence of improved outcome with other pharmacology agents
• Corticosteroids
• Bronchodilators
• Pulmonary vasodilators
• Be conservative with fluid therapy.
• Grave prognosis; survival rates are around 10-20% in veterinary medicine, even with mechanical ventilation

Transfusion-related Acute Lung Injury (TRALI)

• Subset of ARDS associated with blood product transfusions.
• Blood product components cause neutrophils to sequester in the lungs, initiating inflammation.
• Thoracic radiographs show bilateral, pulmonary interstitial to alveolar infiltrates
• Treatment: Oxygen therapy and supportive care.

Negative Pressure Pulmonary Edema

• Causes: Strangulation, choking, near hanging, upper airway obstruction
• Forcible inspiration against a closed glottis causes a dramatic decrease in intrathoracic pressure.
• Decrease in pulmonary interstitial hydrostatic pressure, increase in venous return to the right heart and lungs, both increase the pressure gradient between pulmonary interstitial fluid and pulmonary vessels. Fluid leaks from capillaries into the interstitial space.

Neurogenic Pulmonary Edema (NPE)

• Following post-traumatic brain injuries or seizures.
• Pathophysiology: Fulminant sympathetic stimulation leading to an increase in systemic arterial and venous pressure, combined with a concurrent increase in capillary permeability.
• Diagnosis: Bilateral, diffuse interstitial to alveolar pulmonary pattern on thoracic radiographs.
• Treatment: Oxygen therapy and treatment of the underlying disease.
• Prognosis: Good with supportive care.

Electrocution

• Subcategory of neurogenic pulmonary edema (NPE).
• Extreme sympathetic stimulation.
• Similar to NPE in terms of pathophysiology and diagnosis. Has a good prognosis with supportive care.

Case Study: Wavy, 4-month-old MI Pit Bull Terrier

• Oxygen therapy and anxiolysis were included in the treatment plan.

Pulmonary Hemorrhage

• Bleeding from any site at or below the larynx level.
• Infectious causes (heartworm, leptospirosis)
• Foreign bodies (tracheal)
• Neoplasia
• Bleeding disorders (thrombocytopenia, coagulopathy)
• Contusions (blunt force trauma)

Pulmonary Contusions

• Chest wall impact causes lung injury or bursting.
• Hemorrhage or fluid exudation into the parenchyma.
• worsens over 24-48 hrs post injury
• Diagnosis uses Thoracic radiographs, Lung ultrasounds, CT, Transtracheal wash (TTW), Bronchoalveolar lavage (BAL), and bloodwork (CBC, Coags)
• Treatment include Oxygen therapy, Anxiolysis/Sedation, treat underlying condition

Diagnosis Summary

• Thoracic radiographs (variable, non-specific, focal, interstitial or alveolar pattern)
• Lung ultrasound
• CT scan
• Transtracheal wash (TTW)
• Bronchoalveolar lavage (BAL)
• Bloodwork (CBC, Coags)

Treatment Summary

• Oxygen therapy
• Anxiolysis/sedation
• Treat the underlying disease

Prognosis Summary

• Prognosis depends on the underlying condition.
• Hemorrhage may result from contusions, foreign bodies, or pneumonia and have excellent survival once discharged.

Further Questions

• Methods to assess the correct underlying condition given different clinical signs, physical exam findings, and diagnostics.

This quiz covers non-infectious lung diseases in small animals as discussed in VETM5291 Spring 2025. It includes clinical signs, disease processes such as NCPE and pulmonary hemorrhage, and physical exam findings related to pulmonary parenchymal diseases. Test your knowledge and understanding of these critical aspects of veterinary medicine.