When central venous pressure and pleural (intrathoracic) pressure are both 10 cm H₂O, resulting in zero transmural pressure, does high positive end‑expiratory pressure (PEEP) cause CVP to overestimate right‑atrial filling?

Yes, CVP Overestimates Right Atrial Filling When High PEEP Elevates Pleural Pressure

When CVP and pleural pressure are both elevated (e.g., both 10 mmHg), the transmural pressure (CVP minus pleural pressure) approaches zero, meaning CVP grossly overestimates true right atrial filling—this is precisely what occurs with high PEEP ventilation.

The Core Physiological Problem

The critical issue is that CVP measures intraluminal (intracavitary) pressure, not transmural pressure, which is what actually determines ventricular filling 1. Transmural pressure equals intracavitary pressure minus the surrounding pleural/pericardial pressure. When PEEP increases pleural pressure substantially, CVP rises in parallel but cardiac filling does not improve—in fact, it often worsens 1.

How PEEP Creates This Mismatch

• PEEP increases pleural pressure proportionally: In normal subjects, approximately 50% of alveolar pressure transmits to pleural pressure; in stiff ARDS lungs, less is transmitted but the effect remains significant 1
• CVP rises with pleural pressure: When PEEP is applied, CVP increases because the right atrium is surrounded by elevated intrathoracic pressure 1
• The venous return gradient collapses: The normal pressure gradient from peripheral veins to the right atrium is only 4-8 mmHg 1. Small increases in right atrial back-pressure from PEEP can dramatically reduce venous return
• Transmural pressure falls or becomes zero: If both CVP and pleural pressure rise equally (your example of both at 10 mmHg), transmural pressure = 0, meaning the atrium has no true filling pressure despite an apparently "normal" CVP of 10 mmHg

Clinical Implications and Monitoring Strategy

Measuring Esophageal Pressure is the Gold Standard

To accurately assess right atrial filling during high PEEP, measure esophageal pressure (a surrogate for pleural pressure) and calculate transmural CVP (CVP minus esophageal pressure) 1. This reveals true preload status. Unfortunately, esophageal pressure monitoring remains challenging to implement routinely 1.

Practical Bedside Approach Without Esophageal Pressure

When esophageal pressure is unavailable:

• Use CVP trends, not absolute values: The 2025 ESICM guidelines emphasize CVP should not target specific numbers but rather guide understanding of shock type and fluid response 2
• Very low CVP suggests hypovolemia; high CVP suggests cardiac involvement or RV failure 2
• Calculate organ perfusion pressure gradient (MAP - CVP): This better predicts organ dysfunction than MAP alone 2
• Monitor CVP response to interventions: Rising CVP with fluid administration may signal RV failure rather than adequate resuscitation 2

Echocardiography is Essential

Perform echocardiography early to directly visualize RV size and function 2, 1. Look for:

• RV dilation (RV end-diastolic area/LV end-diastolic area ratio >0.6 indicates acute cor pulmonale) 1
• Paradoxical septal motion during end-systole 1
• IVC characteristics (though less reliable during mechanical ventilation) 1

This directly assesses whether the heart is truly underfilled versus facing excessive afterload from PEEP.

Common Pitfalls to Avoid

1. Do not use CVP targets (8-12 mmHg) for fluid resuscitation: These arbitrary targets from early goal-directed therapy trials have been discredited 2. The FACCT trial showed conservative fluid strategies (lower CVP targets) improved outcomes in ARDS 2

2. Do not assume high CVP means adequate filling during high PEEP: This is the exact scenario you describe—high CVP with high pleural pressure yields zero transmural pressure and poor filling

3. Recognize that pulse pressure variation (PPV) may be misleading: High PPV during high PEEP with low lung compliance may indicate RV afterload dependence rather than fluid responsiveness 1. If PPV remains high despite low tidal volumes, consider RV dysfunction

4. Elevated CVP is a safety signal: High CVP indicates risk of tissue edema, hepatic dysfunction, renal dysfunction, and harm from additional fluids 2. Aim for the lowest CVP associated with adequate cardiac output and tissue perfusion 2

The Right Approach During High PEEP

When managing patients on high PEEP:

• Prioritize RV-protective ventilation: Low driving pressure, limited hypercapnia, PEEP adapted to lung recruitability 1
• Consider prone positioning to improve RV function 1
• Use vasopressors (norepinephrine) rather than excessive fluids when CVP is already elevated 1
• Consider inhaled pulmonary vasodilators if RV afterload is excessive 1
• If available, measure pulmonary artery pressures to directly assess RV afterload and calculate transmural filling pressures 1

The 2016 expert consensus specifically warns that during PEEP, calculating transmural PAOP (wedge pressure minus pleural pressure) allows estimation of true LV filling pressure 1, and the same principle applies to CVP for RV filling assessment.