VETM5291 Pulmonary Parenchymal Diseases

Small Animal Pulmonary Parenchymal Diseases

• These diseases are non-infectious.

• The course was given by Meghan Fick DVM MS DACVECC, Clinical Assistant Professor of Emergency and Critical Care.

• The course is for VETM5291 Spring 2025.

Brief Outline

• Topics include brief clinical signs/physical exam review of pulmonary parenchymal disease.
• Diseases processes include Non-cardiogenic pulmonary edema (NCPE), pulmonary hemorrhage, and pulmonary contusions.

Pulmonary Parenchyma

• Parenchyma is the functioning part of an organ.
• The pulmonary parenchyma includes alveoli, pulmonary microvasculature, and interstitial tissues.
• The alveoli exchange gases (CO2 and O2) in the pulmonary capillaries.

Clinical Signs

• Clinical signs include cough, exercise intolerance, tachypnea, excessive panting, and increased respiratory effort (leading to respiratory distress).

Physical Exam

• Exam findings include inspiratory and/or expiratory effort, increased or decreased bronchovesicular sounds, crackles, and cyanosis.

Helpful Information

• Clinical signs and physical exam findings can mimic other diseases like airway, pleural space, and mediastinal diseases.
• Non-respiratory causes of tachypnea should also be considered.

Step 1: Stabilize Patient First

• Initial treatment involves stabilization of the patient.
• Procedures can include administering oxygen, anxiolysis/sedation.

Pulmonary Edema

• Edema is abnormal fluid accumulation in tissues.
• Edema in the pulmonary interstitium/alveoli can be caused by changes in capillary pressures and permeability.
• Edema in the extravascular space may exceed the capacity of pulmonary lymphatic drainage.
• There are three classifications of Pulmonary Edema (High pressure PE, Increased permeability PE, and Mixed PE).

Pulmonary Edema MOA - 3 classifications

• High pressure PE:
• Cardiogenic in nature causing fluid issues.
• Treated with fluid therapy
• Increased permeability PE:
• ARDS and TRALI are involved with this category.
• Mixed PE:
• Can be caused by negative pressure
• Examples are Neurogenic causes/electrocution.

Pulmonary Edema - Underlying Pathology

• Cardiogenic: Increases in pulmonary transcapillary pressure due to elevated left atrial pressure.
• Non-cardiogenic: Increased pulmonary transcapillary pressure without elevated left atrial pressure due to increased vascular permeability or a combination.

Cardiogenic Pulmonary Edema

• Most common in veterinary medicine
• Typically develops gradually.
• Pathogenesis: Left-sided cardiac failure leads to increased left atrial pressures, increasing pulmonary venous pressures, increasing pulmonary capillary pressures, causing fluid leakage into the pulmonary parenchyma.
• Treatment: Diuretics and treating the underlying condition

Diagnosis

• Thoracic radiographs, echocardiogram, CT scans, and edema fluid protein levels help diagnosis.

Non-cardiogenic Pulmonary Edema

• Acute respiratory distress syndrome (ARDS): Hypoxic respiratory failure secondary to increased capillary permeability.
• Transfusion-related acute lung injury (TRALI): A subset of ARDS linked to blood product transfusions.
• Negative pressure pulmonary edema (NPPE): Also called post-obstructive pulmonary edema (POPE). Caused by forcible inspiration against a blocked glottis.

Acute Respiratory Distress Syndrome (ARDS)

• ARDS is a clinical syndrome characterized by hypoxic respiratory failure.
• It's caused by severe pulmonary edema due to increased capillary permeability, which is triggered by underlying local (pulmonary) or systemic (extra-pulmonary) inflammatory processes.

Causes of ARDS in Dogs and Cats

• Pulmonary: Aspiration pneumonia, pneumonia, pulmonary contusions, chest trauma, mechanical ventilation.
• Extra-pulmonary: Sepsis, systemic inflammatory response syndrome (SIRS), shock, pancreatitis, trauma, and acute kidney injury (AKI).

Pathophysiology of ARDS

• Lung insult (local or systemic injury) triggers the acute exudative phase.
• Fluid, proteins, red blood cells, and white blood cells leak into the alveoli, activating the immune system.
• Subsequent fibroproliferative phase involves proliferation of type II pneumocytes and interstitial fibrosis.

Diagnostic Criteria for ARDS

• Timing: Acute onset (less than 72 hours).
• Diagnostics: Bilateral, diffuse pulmonary infiltrates on thoracic radiographs; high protein edema fluid.
• Oxygenation: Insufficient gas exchange indicated by blood gas analysis.

Treatment and Prognosis for ARDS

• Treatment: Oxygen therapy (often requiring mechanical ventilation); no evidence for improved outcome using other pharmacologies like corticosteroids, bronchodilators, or pulmonary vasodilators.
• Prognosis: Grave; survival rates averaging 10-20% even with mechanical ventilation.

Transfusion-related Acute Lung Injury (TRALI)

• A subset of ARDS associated with blood product transfusions.
• Components of the transfused blood products trigger neutrophil sequestration in the lungs, leading to inflammation.
• Diagnosis involves bilateral pulmonary interstitial to alveolar infiltrates on thoracic radiographs.

Negative-pressure Pulmonary Edema

• Causes: Strangulation, choking, near-hanging, upper airway obstruction.

Pathophysiology of Negative Pressure Pulmonary Edema

• Forcible inspiration against a closed glottis leads to a drop in intrathoracic pressure.
• Decreased pulmonary interstitial hydrostatic pressure, and increased venous return to the right heart and lungs, cause a pressure gradient that forces fluid from capillaries into the interstitial space.

Neurogenic Pulmonary Edema (NPE)

• Caused by post-traumatic brain injury or seizures.
• Pathophysiology involves fulminant sympathetic stimulation, increasing systemic arterial and venous pressure, and concurrent capillary permeability increase.
• Diagnosis involves bilateral, diffuse interstitial to alveolar pulmonary infiltrates on imaging.

Electrocution

• A form of neurogenic pulmonary edema.
• Pathophysiology is similar to NPE.

Diagnosis Summary

• Diagnosis strategies include history taking (patient history).
• Key clinical signs of respiratory distress should be assessed.
• A physical exam, and appropriate diagnostics including, but not limited to, thoracic radiographs and bloodwork/coagulates, and ultrasound/TTW/BAL, should be performed

Treatment Summary

• Oxygen therapy and anxiolysis/sedation should be considered.
• Treatment of the underlying condition along with supportive care should also be included in treatment plans.

Pulmonary Hemorrhage

• Bleeding from any site at or below the larynx level.

• Often associated with infectious causes (i.e., heartworm, leptospirosis), foreign bodies (tracheal), neoplasia, bleeding disorders (e.g., thrombocytopenia, coagulopathy), or contusions (blunt force trauma).

Pulmonary Contusions

• Chest wall impact resulting in lung injuries.
• Hemorrhage and fluid accumulate within the lung parenchyma.
• Symptoms worsen over 24-48 hours post-injury.

This quiz focuses on non-infectious pulmonary parenchymal diseases covered in VETM5291 Spring 2025. Key topics include clinical signs, physical examination, and specific disease processes like NCPE and pulmonary hemorrhage. Assess your understanding of the pulmonary structure and related conditions in small animals.