Balancing Pulmonary Flow and Cardiac Function

Concept of Palliation

A central principle of congenital heart disease palliation is maintaining a balance between pulmonary blood flow (PBF) and cardiac function. When these elements are in equilibrium, circulation is stable and the patient avoids both congestive heart failure and severe cyanosis. In complex congenital circulations, the shared therapeutic aim is to reach and sustain this physiologic balance, often framed with the Qp/Qs concept and oxygen-delivery goals [1].

Optimal State

In the optimal state, pulmonary flow is matched to ventricular capacity: oxygenation is adequate without excessive volume or pressure load. Many programs operationalize this as balanced Qp:Qs near ~1 (often acceptable within ~1–1.5 depending on context) and oxygen saturation targets ~75–85% when appropriate—guarding against occult pulmonary “steal” while preserving systemic delivery especially in single ventricle physiology [1–4].

Increased Pulmonary Flow

When pulmonary flow is excessive, systemic saturation rises but ventricular volume load increases, predisposing to congestive heart failure. Pulmonary artery banding (PAB) can be used to restrict PBF, reduce volume overload, and restore balance; modeling and clinical series support the rationale for limiting excessive Qp to optimize global oxygen delivery and outcomes [2,3].

Decreased Pulmonary Flow

When pulmonary flow is insufficient, ventricular volume burden falls but systemic oxygen delivery worsens (cyanosis). Creating or adjusting a systemic-to-pulmonary shunt can augment PBF and improve oxygenation; titration is guided by perfusion and saturation trends, recognizing that pulmonary venous desaturation (e.g., atelectasis, edema) can confound Qp/Qs inference and must be addressed (ventilation/PEEP/FiO₂) [3,5]. In select settings, shunt banding or controlled adjustments to inflow/outflow can fine-tune the balance [6].

Clinical Perspective

Think of PBF and ventricular performance as a seesaw: too much flow risks failure; too little risks hypoxemia. Management lever options include surgical (PAB, shunts/adjustments) and physiologic (FiO₂, ventilation, afterload/vasoactive strategy) to steer toward a balanced state. NIRS/SvO₂ monitoring supports bedside assessment of perfusion and oxygen delivery, and gas-mixture strategies have been used to modulate Qp when needed, with careful attention to systemic delivery and neurologic safety [4,7].

References

[1] Francis D, Willson K, Thorne S, Davies L, Coats A. Oxygenation in patients with a functionally univentricular circulation and complete mixing of blood: are saturation and flow interchangeable? Circulation. 1999. doi:10.1161/01.CIR.100.21.2198.

[2] Barnea O, Austin E, Richman B, Santamore W. Balancing the circulation: theoretic optimization of pulmonary/systemic flow ratio. J Am Coll Cardiol. 1994. doi:10.1016/0735-1097(94)90123-6.

[3] Photiadis J, Sinzobahamvya N, Fink C, Schneider MBE, et al. Optimal pulmonary to systemic blood flow ratio for best hemodynamic status and outcome early after palliative cardiac surgery. Eur J Cardiothorac Surg. 2006. doi:10.1016/J.EJCTS.2005.12.043.

[4] Magoon R, Makhija N, Jangid S. Balancing a single-ventricle circulation: ‘physiology to therapy’. Indian J Thorac Cardiovasc Surg. 2020. doi:10.1007/s12055-019-00889-w.

[5] Taeed R, Schwartz S, Pearl J, Raake J, Beekman R, et al. Unrecognized Pulmonary Venous Desaturation Early After Norwood Operation Confounds Qp:Qs Assessment and Compromises Oxygen Delivery. Circulation. 2001. doi:10.1161/01.CIR.103.22.2699.

[6] Atlin C, Haller C, Honjo O, Jegatheeswaran A, van Arsdell G, et al. Balancing pulmonary blood flow: Theory, in vitro model, and clinical applications. J Thorac Cardiovasc Surg. 2016. doi:10.1016/j.jtcvs.2016.07.081.

[7] Thomas L, Flores S, Wong J, Loomba R. Acute Effects of Hypoxic Gas Admixtures on Pulmonary-Systemic Blood Flow Ratio in Children Awaiting Norwood Palliation. Cureus. 2019. doi:10.7759/cureus.5693.