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Eur J Cardiothorac Surg 2006;30:693-694
© 2006 Elsevier Science NL
Editorial |
84 Harley Street, London W1G 7HW, United Kingdom
* Corresponding author. Tel.: +44 20 7034 8806; fax: +44 20 7034 8808. (Email: marc.deleval{at}hcahealthcare.co.uk).
In this issue of the journal, Dr Pouard and his colleagues [1] demonstrate that a neonatal arterial switch operation can be performed using continuous normothermic cardiopulmonary bypass (CPB) and they suggest that this may have some advantages.
This achievement would have been unthinkable when the arterial switch operation first became part of our surgical armamentarium. Many factors have contributed to such a ‘tour de force’: advances in surgical techniques, refinement of bypass technology and, not least, an ever-higher level of human performance.
A first reaction would be to support the view that normothermia being more physiological, one could recommend normothermic cardiopulmonary bypass for neonatal cardiac surgery, having demonstrated its feasibility.
After reflection, however, one has to remember that CPB is a highly unphysiological state and the question arises whether normothermic continuous perfusion for neonatal cardiac surgery is the best strategy to alleviate or prevent the consequences of those physiological perturbations.
Two sets of observations would corroborate the normothermic perfusion. The first one is the extensive experience with normothermic CPB in adult cardiac surgery, as referred to by Dr Pouard. The second one, which is perhaps more compelling for this discussion, is the very large experience with neonatal normothermic CPB for acute respiratory failure (extracorporeal membrane oxygenation, ECMO).
Extrapolation of these observational data to neonatal cardiac surgery must be done with great circumspection. Newborn infants are more vulnerable to the physiological insult of CPB; there is a greater metabolic demand of the developing organs; there is a greater disparity between the extracorporeal circuit and the patient's size.
Furthermore, pre-existing morbidity, such as prematurity, cyanosis and cerebral anomalies, may put these neonates at greater risk. Cerebral magnetic resonance imaging abnormalities have been found in 33% of cardiac neonates [2].
A recent review of the practice of CPB in adults reports on ten randomized control trials evaluating neurological outcomes associated with temperature management during CPB. Six trials concluded that there was no difference between normothermic and hypothermic CPB, three reported poorer outcomes with normothermic CPB and one found poorer outcomes with hypothermic CPB [3].
ECMO support, a closed circuit CPB, does not result in the same degree of activation of the various inflammatory cascades and coagulopathies that can lead to post-cardiac surgical multiorgan dysfunction. They result from mechanical sheer stresses induced, for example, by blood suctioning devices, bleeding, blood transfusion, tissue injury, microemboli, multiple manipulations of cardiovascular structures, etc.
Could these disturbances be minimized by some degree of hypothermia with intermittent periods of reduced flow?
The clinical outcomes reported by Dr Pouard and his colleagues would suggest that their present protocol is superior to the previous one. Is this all due to the introduction of normothermic CPB or to confounding variables? Could this be due to a better myocardial protection, an abolition of the temperature gradient between the myocardial temperature and the surrounding tissues provided by warm cardioplegia? All units of excellence – and Hopital Necker certainly qualifies for that – have seen that their post-operative intubation time and length of stay in intensive care units decrease over time with different types of perfusion protocols, some using deep hypothermia and total circulatory arrest.
What is the way forward? Dr Pouard and his colleagues must be applauded for having completed this feasibility study. This is a landmark article. What is needed now is convincing evidence of the superiority of normothermic CPB.
This, in my view, requires a prospective randomized study, comparing two well-defined protocols of CPB. It also requires a selection of meaningful markers of post-CPB morbidity, such as inflammatory markers or markers of central nervous system deficit. The hallmark of these markers is uncertainty, as highlighted by Frank Hanley [4] in his excellent Editorial on deep hypothermia and total circulatory arrest versus continuous perfusion. Frank Hanley's concluding remarks are applicable to this discussion: ‘For the foreseeable future, we would have to deal with one of those real life situations for which complete information is not available to guide our decision. Thus, any decision regarding this choice will involve weighing some mix of limited directly applicable evidence, peripheral evidence, logic and experience’.
While waiting for this evidence, I would not neglect the additional safety margin provided by some degree of hypothermia. Redundancy is one of the characteristics of high reliability organisations and systems and this is probably applicable to neonatal cardiac surgery.
References
This article has been cited by other articles:
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  A. J. Rastan, T. Walther, N. A. Alam, I. Daehnert, M. A. Borger, F. W. Mohr, J. Janousek, and M. Kostelka Moderate versus deep hypothermia for the arterial switch operation -- experience with 100 consecutive patients Eur. J. Cardiothorac. Surg., April 1, 2008; 33(4): 619 - 625. [Abstract] [Full Text] [PDF]
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P. Pouard Reply to Cassano and Milella Eur. J. Cardiothorac. Surg., April 1, 2007; 31(4): 755 - 755. [Full Text] [PDF]
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A. F. Corno Normal temperature and flow: are the 'physiological' values so scary? Eur. J. Cardiothorac. Surg., April 1, 2007; 31(4): 756 - 756. [Full Text] [PDF]
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