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(Circulation. 2006;114:1243-1250.)
© 2006 American Heart Association, Inc.

Congenital Heart Disease

Analytical Identification of Ideal Pulmonary-Systemic Flow Balance in Patients With Bidirectional Cavopulmonary Shunt and Univentricular Circulation

Oxygen Delivery or Tissue Oxygenation?

Gerhard-Paul Diller, MD; Anselm Uebing, MD; Keith Willson, MSc, MIPEM; L. Ceri Davies, MD, MRCP; Konstantinos Dimopoulos, MD; Sara A. Thorne, MD, MRCP; Michael A. Gatzoulis, MD, PhD; Darrel P. Francis, MA, MRCP

From National Heart and Lung Institute (G.-P.D., K.D., M.A.G., D.P.F.), Imperial College of Science and Medicine, London, United Kingdom; Adult Congenital Heart Disease Unit (G.-P.D., A.U., K.D., M.A.G.), Royal Brompton Hospital, London, United Kingdom; Department of Paediatric Cardiology and Biomedical Engineering (A.U.), University Hospital of Schleswig-Holstein, Kiel, Germany; International Centre for Circulatory Health (K.W., D.P.F.), Imperial College of Science and Medicine, London, United Kingdom; Royal London Hospital (L.C.D.), London, United Kingdom; and The Queen Elizabeth Hospital (S.A.T.), Edgbaston, Birmingham, United Kingdom.

Correspondence to Dr Gerhard-Paul Diller, MD, National Heart and Lung Institute, Imperial College of Science and Medicine, Dovehouse St, SW3 6LY London, United Kingdom. E-mail g.diller{at}imperial.ac.uk

Received January 26, 2006; revision received May 23, 2006; accepted June 23, 2006.

Background— In the present study, we extended previous mathematical modeling work on patients with bidirectional cavopulmonary ("bidirectional Glenn") anastomosis to assess the potential utility of several descriptors of oxygen status. We set out to determine which of these descriptors best represents the overall tissue oxygenation. We also introduce a new descriptor, SO₂min, defined as the lower of the superior and inferior vena cava oxygen saturations.

Methods and Results— The application of differential calculus to a model of oxygen physiology of patients with bidirectional Glenn allowed simultaneous assessment of all possible distributions of blood flow and metabolic rate between upper and lower body, across all cardiac outputs, total metabolic rates, and oxygen-carrying capacities. When total cardiac output is fixed, although it may intuitively seem best to distribute flow to maximize oxygen delivery (total, upper body, or lower body), we found that for each variable, there are situations in which its maximization seriously deprives flow to the upper or lower circulation. In contrast, maximizing SO₂min always gives physiologically sensible results. If the majority of metabolism is in the upper body (typical of infancy), then oxygenation is optimized when flow distribution matches metabolic distribution. In contrast, if the majority of metabolism is in the lower body (typical of older children and during exercise), oxygenation is optimal when flows are equal.

Conclusions— In patients with bidirectional cavopulmonary anastomosis, because there is a tradeoff between flow distribution and saturation, it is unwise to concentrate on maximizing oxygen delivery. Maximizing systemic venous saturations (especially SO₂min) is conceptually different and physiologically preferable for tissue oxygenation.

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CLINICAL PERSPECTIVE

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