Acute Pulmonary Oedema (Adult)

1. Overview

Acute Pulmonary Oedema (APO) is a life-threatening medical emergency characterised by the rapid accumulation of fluid in the pulmonary interstitium and alveolar spaces. This leads to a catastrophic mismatch in gas exchange and a precipitous decline in lung compliance, manifesting as acute respiratory failure. [1]

The clinical significance of APO is underscored by its status as the leading cause of emergency hospitalization in patients > 65 years. Pathophysiologically, it is most often the result of Cardiogenic failure (elevated pulmonary capillary wedge pressure > 18-20 mmHg), although non-cardiogenic causes (ARDS) must be excluded. [2]

Management has been transformed by the "Triple Therapy" of High-flow Oxygen, IV Vasodilators, and Non-Invasive Ventilation (CPAP). The 2024 standards of care emphasize the "First 60 Minutes" as the golden window for stabilization and the use of Lung Ultrasound (LUS) for immediate bedside quantification of pulmonary congestion. [3]

2. Epidemiology

The Hospital Context

• Incidence: Accounts for 1-2% of all hospital admissions in the Western world.
• Mortality: In-hospital mortality remains high at 5-10%, rising to > 30% if cardiogenic shock is present.
• The "Flash" Phenomenon: Rapid-onset APO (seconds to minutes) is usually associated with acute MI or renovascular hypertension (Pickering Syndrome). [4]

Precipitating Factors (The "CHAMPIT" Mnemonic)

---

3. Aetiology & Pathophysiology

⚠️ THE 7-STEP MOLECULAR MECHANISM (Starling Failure)

1. Haemodynamic Insult: Acute LV dysfunction (systolic or diastolic) leads to a rise in LV End-Diastolic Pressure (LVEDP).
2. Backward Pressure Transmission: High LVEDP is transmitted to the Left Atrium and subsequently to the Pulmonary Veins and Capillaries.
3. Starling Equilibrium Disruption: When pulmonary capillary hydrostatic pressure ($P_c$) exceeds the plasma oncotic pressure ($\pi_c$), the Starling equation ($J_v$) favors massive efflux of fluid into the interstitium.
4. Lymphatic Overload: Initially, pulmonary lymphatics increase flow by 10-fold. Once their capacity is exceeded, fluid accumulates in the loose connective tissue (Interstitium).
5. Alveolar Flooding: Fluid breaches the alveolar-capillary membrane, filling the alveoli with protein-rich transudate. This destroys Surfactant, leading to widespread atelectasis.
6. V/Q Shunt & Hypoxia: Blood flows through non-ventilated (flooded) alveoli, creating a right-to-left shunt. Hypoxaemia triggers a massive Sympathetic Surge (Catecholamine release).
7. The Vicious Cycle: Catecholamines cause systemic vasoconstriction, further increasing LV afterload, which worsens LVEDP and drives more fluid into the lungs. [5, 6, 7]

---

4. Clinical Presentation

Symptoms

• Acute Dyspnoea: "Air hunger" and a sensation of drowning.
• Orthopnoea: Inability to lie flat; patients are often found sitting on the edge of the bed or in the "Tripod" position.
• Agitation: Driven by hypoxia and sympathetic overactivity (the "sense of impending doom").

Physical Signs

1. Pink Frothy Sputum: Pathognomonic for severe APO (plasma mixing with air).
2. Bibasal Fine Crackles: "Velcro-like" inspiratory sounds. In severe cases, these extend to the mid-zones or apex.
3. S3 Gallop: Low-frequency diastolic sound indicating LV failure.
4. LUS B-lines: Bedside ultrasound showing "Comet tails" (> 3 per window) throughout the lung fields. [8]

---

5. Investigations

The Diagnostic Triad

1. CXR: Look for Upper Lobe Diversion, Kerley B lines, and Perihilar Bat-wing opacities.
2. NT-proBNP: Extremely high (> 1000 pg/mL) in acute decompensation. High NPV for ruling out HF.
3. Bedside Echo: Mandatory to assess EF and look for mechanical causes (e.g. acute MR).

Lung Ultrasound (LUS)

LUS is now superior to CXR for early diagnosis. A positive scan requires B-lines (vertical artifacts) in ≥2 zones bilaterally. It is the fastest way to distinguish "Wet Lung" (APO) from "Dry Lung" (COPD/Asthma). [9]

---

6. Management: The First 60 Minutes

1. Positioning & Oxygen

• Sit Upright: Immediate reduction in venous return (preload).
• High-flow O2: Aim for SpO2 > 94%.

2. Non-Invasive Ventilation (CPAP)

• First-line: CPAP (5-10 cmH2O) reduces the need for intubation and mortality.
• Mechanism: Increases intrathoracic pressure, which reduces venous return (preload) and pushes fluid out of the alveoli. [10]

3. Vasodilators (The "Afterload" Priority)

• IV Nitroglycerin: If SBP > 110 mmHg. High-dose boluses (e.g. 2 x 400mcg puffs) or rapid infusion are superior to diuretics for early stabilization in hypertensive APO.
• Nitroprusside: Reserved for refractory hypertensive crisis.

4. Diuretics (The "Volume" Priority)

• IV Furosemide: Dose should be 1-2.5x the patient's daily oral dose.
• Warning: Diuretics take 30-60 mins to cause diuresis; vasodilators work in seconds. [11]

---

7. Evidence: Landmark Trials

---

8. Single Best Answer (SBA) Questions

Question 1

A 75-year-old male with a history of MI presents with severe breathlessness and pink frothy sputum. BP is 185/110, HR 115. ECG shows sinus tachycardia and old Q-waves. What is the most effective immediate intervention to improve his gas exchange and reduce his preload?

• A) IV Furosemide 80mg
• B) CPAP at 10 cmH2O
• C) IV Morphine 5mg
• D) Oral Ramipril 2.5mg
• E) IV Aminophylline
• Answer: B. CPAP provides immediate physiological benefit by recruiting alveoli and increasing intrathoracic pressure, which reduces venous return (preload) and afterload. While diuretics are needed, CPAP and vasodilators are faster in the "Flash" hypertensive presentation.

Question 2

On a bedside lung ultrasound, which finding is most specific for the diagnosis of cardiogenic pulmonary oedema?

• A) A-lines (Horizontal artifacts)
• B) Pleural sliding with "barcode sign"
• C) Bilateral B-lines (> 3 per window)
• D) Subpleural consolidation
• E) Anechoic fluid in the costophrenic angle
• Answer: C. Bilateral, diffuse B-lines (vertical comet-tail artifacts) represent fluid in the interlobular septa and are highly sensitive and specific for pulmonary congestion.

---

9. Viva Scenario: The "Cold and Wet" Shock

Examiner: "Your patient has bilateral crackles and orthopnoea, but their BP is 82/50 and they are cold to the touch. Can you use CPAP and GTN?"

Candidate:

1. Haemodynamic Profile: This is Cardiogenic Shock (Cold and Wet).
2. Contraindication: IV vasodilators (GTN) are strictly contraindicated as they will worsen the hypotension and coronary perfusion.
3. NIV Nuance: CPAP must be used with extreme caution (or avoided) as the increased intrathoracic pressure can further reduce venous return and cause total circulatory collapse in a shocked patient.
4. Priority: The priority is Inotropic support (e.g. Dobutamine) and urgent Cardiology/ICU review for mechanical support (IABP/Impella).
5. Diuresis: I would use very small doses of IV Furosemide only once the BP is supported.

---

10. Patient Explanation

"Acute pulmonary oedema is a condition where your lungs have suddenly 'flooded' with fluid. This happens because your heart is struggling to pump blood forward, causing it to back up into the lung's air sacs. It feels like you are drowning because, in a way, you are. We are using this tight-fitting mask (CPAP) to push the fluid out of your lungs and give you medications through a drip to relax your blood vessels and flush the extra fluid out via your kidneys."

---

11. References

1. McDonagh TA, et al. 2021 ESC Guidelines for the diagnosis and treatment of acute and chronic heart failure. Eur Heart J. 2021. [PMID: 34447992]
2. NICE NG106. Chronic heart failure in adults: diagnosis and management. 2018. NICE
3. Gray A, et al. Noninvasive Ventilation in Acute Cardiogenic Pulmonary Edema (3CPO). N Engl J Med. 2008. [PMID: 18614781]
4. Felker GM, et al. Diuretic Strategies in Patients with Acute Decompensated Heart Failure (DOSE). N Engl J Med. 2011. [PMID: 21366472]
5. Lichtenstein DA, Mezière GA. Relevance of lung ultrasound in the diagnosis of acute respiratory failure (BLUE protocol). Chest. 2008. [PMID: 18403664]

---

Last Updated: 2026-01-05 | MedVellum Editorial Team