Ann Thorac Surg 2007;83:1436-1437
© 2007 The Society of Thoracic Surgeons
Original Articles: Cardiovascular
Invited commentary
Ralph Delius, MD
Division of Cardiovascular Surgery, Children’s Hospital of Michigan, 3901 Beaubien Blvd, Detroit, MI 48201-2196
(Email: rdelius{at}dmc.org).
Near-infrared spectroscopy (NIRS), which is a noninvasive technique measuring brain tissue oxygenation, has gained increasing acceptance in congenital heart surgery units as a useful means of assessing cerebral perfusion. The use of NIRS has been extensively studied in the perioperative management of surgical patients. Fenton and colleagues [1] from the Children’s Hospital of Omaha have suggested in this article that cerebral oxygen saturation (ScO2) may have prognostic implications as well. Although the number of patients with dramatically diminished NIRS-derived ScO2 values was low, is not surprising that this study found that these patients are at increased risk of death, because ScO2 is an approximate surrogate for mixed venous oxygen saturation, which in turn has been demonstrated to correlate with poor postoperative outcomes [2]. However, possibly a more significant finding of this study is that patients undergoing single ventricle palliation have ScO2 values which are suggestive of marginal cerebral oxygen delivery and are not improved until an in-series circulation is established at second stage palliation, typically a hemi-Fontan or a bidirectional Glenn shunt. It has long been known that patients in whom a modified Blalock-Taussig shunt is responsible for their entire pulmonary circulation have an "unstable" circulation. The interval mortality between the Norwood procedure and second stage palliation has been well documented, and several strategies have been developed to minimize interstage mortality [3]. The interstage mortality between second stage palliation and completion of a Fontan shunt is strikingly less, underscoring the point that an in-series circulation is more "stable" than a parallel circulation with shunt dependant pulmonary circulation, despite the fact that systemic oxygen saturations are often similar before and after second stage palliation. The impact of chronically low ScO2 saturations on neurologic development remains to be established, but would it not be unreasonable to infer that a correlation may exist. The interstage ScO2 after Sano shunt palliation or the hybrid procedure, in which the branch pulmonary arteries are banded in conjunction with ductus stenting, has not been well characterized. However, preliminary studies have suggested that interim mortality is diminished after Sano shunt palliation compared with patients who have a modified Blalock-Taussig shunt [4]. This raises the question of whether interstage ScO2 levels are different between traditionally shunted patients versus those who are undergoing a Sano shunt or hybrid procedure, and whether there might be improved neurologic outcomes with either of these procedures. Subsequent studies may clarify whether these novel approaches to single ventricle palliation may offer long-term benefits that may not be apparent by studies looking only at perioperative parameters. As with most good studies, the report by Fenton and colleagues [1] raises yet still more questions.
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References
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- Fenton KN, Lessman K, Glogowski K, Fogg S, Duncan KF. Cerebral oxygen saturation does not normalize until after stage 2 single ventricle palliation Ann Thorac Surg 2007;83:1431-1437.[Abstract/Free Full Text]
- Bradley SM, Atz AM. Postoperative management: the role of mixed venous oxygen saturation montoring Semin Thorac Cardiovasc Surg Ann 2005;8:22-27.
- Ghanayem NS, Hoffman GM, Mussatto KA, et al. Home surveillance program prevents interstage mortality after the Norwood procedure J Thorac Cardiovasc Surg 2003;126:1367-1377.[Abstract/Free Full Text]
- Pizarro C, Mroczek T, Malec E, Norwood WI. Right ventricle to pulmonary artery conduit reduces interim mortality after stage 1 Norwood for hypoplastic left heart syndrome Ann Thorac Surg 2004;78:1959-1963.[Abstract/Free Full Text]
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