VETM5291 Small Animal Pulmonary Diseases

Small Animal Pulmonary Parenchymal Diseases

• These diseases are non-infectious
• The presenter is Meghan Fick, DVM, MS, DACVECC, a clinical assistant professor of emergency and critical care.
• The course is VETM5291, Spring 2025.

Brief Outline

• The outline includes a review of pulmonary parenchymal disease, including clinical signs, physical exams, and disease processes.
• Disease processes include Non-cardiogenic pulmonary edema (NCPE), Pulmonary hemorrhage, and Pulmonary contusions.

Pulmonary Parenchyma

• The pulmonary parenchyma is the functional portion of the lung.
• It includes: alveoli, pulmonary microvasculature, and interstitial tissues.
• Oxygen (O₂) and carbon dioxide (CO₂) are exchanged in the alveoli and pulmonary capillaries.

Clinical Signs

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

Physical Exam

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

Helpful Clinical Findings

• Inspiratory effort and expiratory effort are helpful clinical indicators.
• But clinical signs and physical exam findings can mimic airway, pleural space, and mediastinal diseases. Non-respiratory causes of tachypnea also need to be considered.

Stabilization

• The first step is to stabilize the patient.
• This includes administering oxygen and anxiolytics/sedation.

Pulmonary Edema

• Edema is the abnormal accumulation of fluid in tissues.
• Pulmonary edema involves fluid buildup in the pulmonary interstitial space and alveoli.
• It exceeds the capacity of the pulmonary lymphatic drainage.
• Edema is caused by alterations in fluid flow across capillaries and changes in pressures.
• The volume of flow and capillary permeability can alter this process.

Pulmonary Edema MOA - 3 Classifications

• High pressure PE
• Increased permeability PE
• Mixed PE

High Pressure PE

• Cardiogenic (fluid therapy)
• Related to increased left atrial pressure.

Increased Permeability PE

• ARDS
• TRALI
• Related to increased capillary permeability.

Mixed PE

• Negative pressure
• Neurogenic/electrocution
• A combination of the factors above.

Pulmonary Edema - Underlying Pathology

• Cardiogenic pulmonary edema: Increased pulmonary transcapillary pressure due to increased left atrial pressure.
• Non-cardiogenic pulmonary edema: Increased pulmonary transcapillary pressure without increased left atrial pressure, Increased vascular permeability, Combo of both

Cardiogenic Pulmonary Edema

• Most common pulmonary edema in veterinary medicine
• Generally, occurs gradually.
• Pathogenesis: Left sided cardiac failure→ Increased left atrial pressures→ increased pulmonary venous and pulmonary capillary pressures → fluid leaking from vessels into the pulmonary parenchyma.

Diagnosis

• Thoracic radiographs
• Echocardiogram
• CT scans
• Edema fluid protein levels

Non-Cardiogenic Pulmonary Edema

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

Acute Respiratory Distress Syndrome (ARDS)

• ARDS symptoms include:
• Severe hypoxemic respiratory failure
• Severe pulmonary edema due to increased capillary permeability
• Caused by local (pulmonary) or systemic (extrapulmonary) inflammatory processes Causes include aspiration pneumonia, pneumonia, pulmonary contusions, chest trauma, mechanical ventilation, sepsis, systemic inflammatory response syndrome (SIRS), shock, pancreatitis, trauma, and acute kidney injury (AKI).

Pathophysiology of ARDS

• Injury to the lung
• Acute exudative phase with diffuse alveolar damage
• Fluid, proteins, and blood cells leak into alveoli triggering immune system response.
• Fibroproliferative phase with proliferation of type II pneumocytes and interstitial fibrosis.

Diagnostic Criteria for ARDS

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

Treatment & Prognosis for ARDS

• Treatment: Oxygen therapy, potentially needing mechanical ventilation. Corticosteroids, bronchodilators, and pulmonary vasodilators.
• Prognosis (in veterinary medicine): Grave, survival rates range from 10-20% even with mechanical ventilation.

Transfusion-related Acute Lung Injury (TRALI)

• A subset of ARDS associated with blood product transfusions.
• Components of the blood product trigger neutrophils to accumulate in the lungs, causing inflammation.
• Diagnosis - bilateral, pulmonary interstitial/alveolar infiltrates on radiographs
• Treatment - oxygen therapy, supportive care.

Negative-pressure pulmonary edema

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

Pathophysiology of Negative Pressure Pulmonary Edema

• Forcible inspiration against a closed glottis with a rapid decrease in intrathoracic pressure.
• This decreases pulmonary interstitial hydrostatic pressure and increases venous return to the right heart and lungs.
• This increases the pressure gradient between pulmonary interstitium and vessels, leading to fluid leakage from capillaries into the interstitial space.

Wavy the Pit Bull Terrier (Case Study)

• 4-month-old MI Pit Bull Terrier
• Treatment: Oxygen therapy, Anxiolysis

Neurogenic Pulmonary Edema (NPE)

• Post-traumatic brain injury or seizures
• Fulminant sympathetic stimulation
• Increase in systemic arterial and venous pressure
• Concurrent increase in capillary permeability.

Neurogenic Pulmonary Edema (NPE) - Diagnosis and Prognosis

• Thoracic radiographs show bilateral, diffuse interstitial to alveolar pulmonary pattern.
• Treatment involves supplemental oxygen therapy and treatment of underlying disease
• Prognosis is good.

Electrocution

• A subcategory of neurogenic pulmonary edema characterized by extreme sympathetic stimulation.
• Diagnosis through bilateral, diffuse interstitial to alveolar pulmonary pattern via radiographs.
• Prognosis should be good with supportive care.

How to Determine the Cause of Pulmonary Edema

• History
• Clinical signs
• Physical exam
• Diagnostics (Thoracic radiographs, Echocardiogram, CT scans, Edema fluid protein levels)

Pulmonary Hemorrhage

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

Pulmonary Contusions

• Chest wall impact causes injury to the lung
• Hemorrhage and fluid exudate into lung parenchyma.
• Worsens over 24-48 hours after injury.

Pulmonary Contusion - Diagnosis

• Thoracic radiographs – variable, non-specific, often focal diffuse interstitial to alveolar pattern.
• Lung ultrasound (also potentially helpful)
• CT - Transtracheal wash (TTW), bronchoalveolar lavage (BAL), blood work (CBC, Coags)

Pulmonary Contusions - Treatment & Prognosis

• Oxygen therapy, anxiolysis/sedation, treatment of the underlying condition.
• Prognosis depends on the condition driving the contusion (excellent outcome with uncomplicated contusions from FB, foreign bodies, or pneumonia).

Questions

• Contact Meghan Fick at [email protected] with any inquiries.