📚 Guideline basis
Vieillard-Baron and colleagues' body of work defining acute cor pulmonale in ARDS and the RV protective ventilation concept; Repessé X, Vieillard-Baron A (PMID 30603577); Rex et al. Eur Heart J 2022 (PMID 35778820); ASE 2025 right heart guideline; ESICM/ATS ARDS definitions and ventilation guidance.
Pathophysiology & Mechanisms
ARDS imposes right ventricular afterload through four simultaneous mechanisms:
- Pulmonary vascular obliteration and microthrombosis. Endothelial injury, capillary occlusion, and in situ thrombosis reduce the cross-sectional area of the pulmonary vascular bed. Autopsy and CT-angiographic series demonstrate substantial pulmonary vascular occlusion in ARDS independent of macroscopic embolism.
- Hypoxic pulmonary vasoconstriction. Alveolar hypoxia raises pulmonary vascular tone in poorly ventilated regions — teleologically protective for shunt, mechanically costly for the RV.
- Hypercapnic acidosis. PaCO₂ elevation raises pulmonary vascular resistance directly and independently. This is the mechanism by which permissive hypercapnia, a lung-protective strategy, is an RV-hostile strategy.
- Mechanical ventilation. Pulmonary vascular resistance follows a U-shaped relationship with lung volume: minimal at functional residual capacity, rising with both atelectasis (hypoxic vasoconstriction, alveolar vessel tortuosity) and overdistension (compression of alveolar capillaries). High plateau pressure and high driving pressure compress the alveolar vasculature and are the dominant iatrogenic contributor.
The result is acute RV pressure overload in a thin-walled ventricle with no time to hypertrophy. RV dilatation follows, then septal shift, then LV underfilling, then falling systemic output and coronary perfusion pressure — the spiral described in Chapter 9.
Clinical Phenotypes & Epidemiology
Acute cor pulmonale (ACP) occurs in approximately 20–25% of moderate-to-severe ARDS patients ventilated with lung-protective strategies, with higher prevalence at higher driving pressures. It is independently associated with mortality in severe ARDS.
Risk factors identified in the ARDS cohorts (the basis of the "RV-protective" approach):
Risk factor | Threshold |
Pneumonia as the ARDS aetiology | — |
Driving pressure | ≥ 18 cmH₂O |
PaO₂/FiO₂ ratio | < 150 mmHg |
PaCO₂ | ≥ 48 mmHg |
The presence of two or more of these markedly increases the probability of ACP and is the trigger for deliberate RV assessment.
Diagnostic Synthesis
Definition of acute cor pulmonale
Two components, both required:
- RV dilatation: RV end-diastolic area / LV end-diastolic area > 0.6 in the apical four-chamber view (severe if > 1.0)
- Septal dyskinesia: paradoxical systolic septal motion in the parasternal short-axis view at papillary muscle level
Note the definition uses areas, not diameters, and is measured at end-diastole. Septal dyskinesia distinguishes the pressure-overloaded RV from the merely dilated one.
Additional parameters
Parameter | Finding in ACP | Interpretation caveat |
TAPSE | Often reduced (< 1.7 cm) | May be preserved early despite significant dilatation |
RV free wall strain | Reduced (less negative than −20%) | Detects dysfunction before TAPSE |
TAPSE/PASP | < 0.3–0.4 mm/mmHg | The most informative single index of RV–PA coupling |
RVOT acceleration time | < 105 ms; < 60 ms with high PVR | Mid-systolic notching indicates high wave reflection |
TR velocity / PASP | Elevated, but falls as the RV fails | A falling PASP with worsening RV function is deterioration |
RV free wall thickness | < 5 mm in truly acute disease | > 5 mm implies chronic pressure overload and reframes the diagnosis |
IVC | Dilated, minimal respiratory variation | Reflects RV failure, not fluid responsiveness |
The ventilator test
The most useful diagnostic manoeuvre is therapeutic. If acute cor pulmonale is identified, reduce driving pressure and plateau pressure, correct hypercapnia, optimise PEEP toward the point of best compliance, and rescan. Reversal of septal dyskinesia and a fall in RV:LV area ratio confirm that the ventilator was a major contributor and validates the strategy.
Therapeutic Logic — RV-protective ventilation
Target | Rationale |
Plateau pressure < 27–30 cmH₂O | Limit alveolar vascular compression |
Driving pressure < 15–18 cmH₂O | The strongest ventilator-derived predictor of ACP and of mortality |
PaCO₂ < 48 mmHg where achievable | Hypercapnia directly raises PVR; permissive hypercapnia is not RV-neutral |
PEEP titrated to compliance, not to oxygenation alone | Both under- and over-inflation raise PVR |
Prone positioning | Reduces PVR by recruitment and improved V/Q matching, reduces driving pressure, and has been shown to reduce RV dilatation and improve RV function in ARDS with ACP |
Consider ECCO₂R or veno-venous ECMO | Where PVR-driving hypercapnia cannot be corrected within safe pressures |
Prone positioning is the single most effective intervention for ARDS-associated ACP, acting on oxygenation, driving pressure, and PVR simultaneously.
Haemodynamic management
Problem | Action | Avoid |
Hypotension with dilated RV | Noradrenaline to restore coronary perfusion pressure; vasopressin as adjunct (less pulmonary vasoconstriction) | Fluid boluses |
Inadequate RV contractility | Dobutamine or milrinone, recognising the vasodilator effect requires vasopressor cover | High-dose pure beta agents in the tachycardic patient |
High PVR | Inhaled nitric oxide or inhaled prostacyclin — improves oxygenation and lowers PVR without systemic hypotension; no mortality benefit demonstrated | Systemic pulmonary vasodilators (worsen shunt and cause hypotension) |
Fluid overload with congestion | Diuresis or ultrafiltration guided by venous Doppler (Chapter 13) | Continued liberal fluid |
Refractory | VV-ECMO for gas exchange; VA-ECMO or RV assist device for circulatory failure | — |
Fluid is usually the wrong answer in ACP. The dilated, pressure-overloaded RV is on the descending limb: additional preload increases wall stress, worsens septal shift, decreases LV filling, and lowers cardiac output. Where preload deficit genuinely coexists, give small volumes (≤ 250 mL) with immediate reassessment of LVOT VTI and RV:LV ratio.
Distinguishing ARDS from cardiogenic pulmonary oedema
Both produce bilateral B-lines and hypoxaemic respiratory failure. Echocardiography with lung ultrasound resolves most cases:
Feature | Cardiogenic oedema | ARDS |
LV systolic function | Frequently reduced | Usually normal |
E/e′ | Elevated (> 14 average) | Normal |
TR velocity | ≥ 2.8 m/s (post-capillary) | Variable; PASP may be raised with normal LAP indices |
LA volume index | Enlarged | Usually normal |
B-line distribution | Homogeneous, gravity-dependent, bilateral, symmetric | Patchy, spared areas, subpleural consolidation, irregular pleural line |
Pleural line | Smooth, regular | Thickened, irregular, fragmented |
Response to diuresis | B-lines clear rapidly | Little change |
The two coexist frequently. The clinical question is rarely "which one" but "how much of each", and the E/e′ and TR velocity pair is the most useful discriminator obtainable at the bedside.
🛑 Critical pitfall: Attributing a dilated RV in ARDS to pulmonary embolism without evidence. ACP is a far commoner explanation in ventilated ARDS, and anticoagulating or thrombolysing on RV dilatation alone is unjustified without imaging confirmation.
🛑 Critical pitfall: Interpreting a falling PASP in a deteriorating ARDS patient as improving pulmonary vascular resistance. A failing RV cannot generate pressure. Read PASP alongside TAPSE, RV:LV ratio, and RVOT VTI.
🛑 Critical pitfall: Treating ACP-associated hypotension with fluid. It reliably worsens the physiology.
- 💡 Clinical pearl: Scan the RV in every ARDS patient with driving pressure ≥ 18 cmH₂O, PaO₂/FiO₂ < 150, PaCO₂ ≥ 48 mmHg, or a pneumonic aetiology — before the patient becomes shocked.
- 💡 Clinical pearl: The ventilator is a right ventricular drug. In ACP, the first therapeutic step is at the ventilator, not the syringe driver.
- 💡 Clinical pearl: RV free wall thickness ≥ 5 mm in a patient presenting with "acute" RV failure means the process is not acute. Reframe the differential toward chronic pulmonary hypertension.
References
- Vieillard-Baron A, Naeije R, Haddad F, et al. Diagnostic workup, etiologies and management of acute right ventricle failure. Intensive Care Med 2018;44:774–90.
- Repessé X, Vieillard-Baron A. Right heart function during acute respiratory distress syndrome. PMID 30603577.
- Mekontso Dessap A, Boissier F, Charron C, et al. Acute cor pulmonale during protective ventilation for ARDS: prevalence, predictors, and clinical impact. Intensive Care Med 2016;42:862–70.
- Rex et al. Right heart assessment in the perioperative and critical care setting. Eur Heart J 2022. PMID 35778820.
- American Society of Echocardiography. Guidelines for the echocardiographic assessment of the right heart in adults and special considerations in pulmonary hypertension. J Am Soc Echocardiogr 2025.