Pulmonary Edema
Definition
Pulmonary edema is the abnormal accumulation of fluid in the lung interstitium and alveoli, leading to impaired gas exchange and hypoxemia.
Classification
1. Based on Mechanism
|
Type |
Mechanism |
Examples |
|
Cardiogenic (Hydrostatic) |
↑ Pulmonary capillary hydrostatic pressure |
LV failure, MI |
|
Non-cardiogenic (Permeability) |
↑ Capillary permeability |
ARDS, sepsis |
|
Mixed |
Both mechanisms |
Sepsis + LV dysfunction |
2. Based on Time Course
- Acute pulmonary edema (APE) → life-threatening emergency
- Chronic pulmonary congestion → seen in chronic HF
Cardiogenic Pulmonary Edema
Primary driver: ↑ Pulmonary capillary pressure (>18 mmHg)
Sequence:
- LV dysfunction → ↑ LVEDP
- ↑ Left atrial pressure
- ↑ Pulmonary venous pressure
- Fluid → interstitium → alveoli
Non-Cardiogenic Pulmonary Edema (ARDS-type)
- Normal/low PCWP (<18 mmHg)
- ↑ Capillary permeability
- Protein-rich fluid → alveoli
- Loss of surfactant → alveolar collapse
Etiology
Cardiogenic Causes
- Acute MI
- Acute decompensated heart failure
- Severe hypertension
- Valvular disease (MR, AR, MS)
- Arrhythmias (AF with RVR)
Non-Cardiogenic Causes
- ARDS (sepsis, trauma)
- Aspiration
- TRALI
- Neurogenic pulmonary edema
- High altitude pulmonary edema (HAPE)
- Acute kidney failure (fluid overload)
Clinical Features
Symptoms
- Severe dyspnea (orthopnea, PND)
- Cough with pink frothy sputum
- Anxiety, air hunger
Signs
|
System |
Findings |
|
General |
Tachypnea, diaphoresis |
|
CVS |
S3 gallop (cardiogenic) |
|
RS |
Bilateral crepitations, wheeze (“cardiac asthma”) |
|
Severe |
Hypoxia, altered sensorium |
Investigations
1. Bedside
- SpO₂ ↓
- ABG:
- Early: respiratory alkalosis
- Late: respiratory acidosis
2. Imaging
Chest X-ray Findings
- Cardiomegaly (cardiogenic)
- Bat-wing pattern(Bilateral, symmetric perihilar opacities),
- Kerley B lines
- Pleural effusion
|
Stage |
Finding |
|
Interstitial edema |
Kerley B lines, peribronchial cuffing |
|
Alveolar edema |
Bat-wing pattern appears |
Why Perihilar (Central) Distribution? — THE REAL QUESTION
A. Anatomy of Pulmonary Blood Flow
- Hilar region = maximum vascular density
- More capillaries → more fluid leak
B. Gravity & Perfusion
- Central lung zones receive higher blood flow
- Hence higher hydrostatic pressure
C. Lymphatic Drainage Pattern
- Peripheral lung fields have better lymphatic clearance initially
- So fluid accumulates centrally first
|
Feature |
Cardiogenic Edema |
Non-cardiogenic (ARDS) |
|
Distribution |
Central (bat-wing) |
Peripheral |
|
Heart size |
Enlarged |
Normal |
|
Kerley B lines |
Present |
Rare |
|
Pleural effusion |
Common |
Less common |
3. Echocardiography
- EF assessment
- Valvular pathology
- Diastolic dysfunction
4. Hemodynamics (Swan-Ganz)
|
Parameter |
Cardiogenic |
Non-cardiogenic |
|
PCWP |
↑ (>18 mmHg) |
Normal (<18) |
|
Cardiac output |
↓ |
Normal/↑ |
5. Biomarkers
- BNP/NT-proBNP ↑ → cardiogenic
- Troponin → MI
Management
Acute Pulmonary Edema (ICU Emergency)
1. Position
- Propped-up (Fowler’s position) → ↓ venous return
2. Oxygen & Ventilation
|
Modality |
Indication |
|
Oxygen |
Mild |
|
NIV (CPAP/BiPAP) |
First-line (reduces intubation, mortality) |
|
Mechanical ventilation |
Severe hypoxia/fatigue |
3. Pharmacological Therapy
Loop Diuretics
- Furosemide
- Dose: 20–40 mg IV (titrate)
- Effect: ↓ preload
Vasodilators (Key Therapy)
- Nitroglycerin (IV)
- First-line in hypertensive APE
- ↓ preload & afterload
Morphine ( Now controversial)
- Use limited (respiratory depression risk)
Inotropes (if shock)
- Dobutamine
- Noradrenaline (if hypotension)
4. Fluid Management
- Strict input-output
- Avoid fluid overload
5. Treat Underlying Cause
- MI → revascularization
- Arrhythmia → control
- Valvular → surgery
Special Situations
Flash Pulmonary Edema
- Sudden onset
- Severe hypertension
- Requires high-dose nitrates + NIV
Neurogenic Pulmonary Edema
- CNS injury → sympathetic surge
- Management: supportive
High Altitude Pulmonary Edema (HAPE)
- Hypoxia-induced vasoconstriction
- Treatment:
- Oxygen
- Descent
- Nifedipine