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Eur J Cardiothorac Surg 2006;29:551-556
© 2006 Elsevier Science NL

Optimal pulmonary to systemic blood flow ratio for best hemodynamic status and outcome early after Norwood operation

^a Department of Paediatric Thoracic and Cardiovascular Surgery, German Paediatric Heart Institute, Arnold Janssen-Strasse 29, D-53757 Sankt Augustin, Germany
^b Department of Cardiac Intensive Care, German Paediatric Heart Institute, Sankt Augustin, Germany
^c Department of Paediatric Cardiology, German Paediatric Heart Institute, Sankt Augustin, Germany
^d Department of Anesthesiology and Critical Care Medicine, German Paediatric Heart Institute, Sankt Augustin, Germany

Received 19 September 2005; received in revised form 6 December 2005; accepted 23 December 2005.

^_* Corresponding author. Tel.: +49 2241 249 600; fax: +49 2241 249 602. (Email: photiadis{at}gmx.de).

Objective: Imbalances of pulmonary to systemic blood flow ratio (Q _p/Q _s) compounded with inadequate systemic oxygen delivery correlate with mortality after first-stage Norwood palliation of hypoplastic left heart syndrome. Mathematical models suggest that maximal systemic oxygen delivery occurs with Q _p/Q _s of less than 1. Whether this applies to clinical practice is unclear. This study evaluates the level of Q _p/Q _s that correlates with best hemodynamic status in the first 48 postoperative hours. Methods: Hemodynamic data of 25 consecutive patients who underwent Norwood procedure from October 2002 to January 2005 were retrospectively analyzed. Data included, in particular, systemic venous and arterial oxygen saturation (SvO₂ and SaO₂, respectively), Q _p/Q _s, lactate levels, and doses of required inotropes. Parameters were recorded 3 hourly. Data were assigned to three groups according to their corresponding Q _p/Q _s: Groups 1, 2, and 3 for Q _p/Q _s 1, Q _p/Q _s between 1 and 2, and Q _p/Q _s 2, respectively. Thereafter, independent t-test or Fisher's exact test was used to reveal significant differences. Q _p/Q _s ratios and lactate levels were compared in hospital survivors and non-survivors. Results: Out of 343 samples, 110, 184, and 49 were assigned to groups 1, 2, and 3, respectively. Group 1 (Q _p/Q _s 1) was characterized by lower SaO₂ (p < 0.001) with similar SvO₂ (p = 0.3 and p = 0.5) and, therefore, higher systemic oxygen delivery (arteriovenous oxygen saturation difference, p < 0.001; oxygen excess factor, p < 0.001) compared to groups 2 and 3. However, lower mean arterial pressure (p = 0.07 and p < 0.001), higher lactate levels (p = 0.009 and p = 0.01), and norepinephrine doses (p = 0.006 and p < 0.001) highlighted worse hemodynamics. The best hemodynamic status corresponded to group 2. Q _p/Q _s remained above 1 in 21 survivors and was, most of the times, below 1 in four patients who died. Lactate levels were almost always above 4 mmol/l or increasing in non-survivors. Conclusions: Maximum oxygen delivery after Norwood operation occurs at Q _p/Q _s of less than 1. However, optimal hemodynamic status and end-organ function and higher survival correlates with Q _p/Q _s between 1 and 2. Thus, Q _p/Q _s should be targeted at 1.5 for improved course early after first-stage Norwood palliation.

Key Words: Norwood • Hemodynamics • Pulmonary/systemic blood flow ratio

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