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Ann Thorac Surg 2007;83:1803-1804
© 2007 The Society of Thoracic Surgeons
Department of Anesthesiology, Maisonneuve-Rosemont Hospital, 5415 L’Assomption Blvd, Montreal, QC, H1T 2M4 Canada
(Email: joanne.guay{at}umontreal.ca).
Odegard and colleagues [1] are reporting decreased blood levels of various procoagulant and anticoagulant factors in children with two-ventricle congenital heart disease (CHD) under 4 years of age. The clinical implications of these findings are unclear. First, measuring the quantity of factors does not tell us how the system reacts globally. Apart from factor VIII, all coagulation factors are decreased at birth and an altered platelet function during the first years of life has also been shown [2]. Yet when the coagulation of infants is evaluated with a thromboelastograph, a relative hypercoagulable state is found [3]. Likewise, children with CHD have many specific hemostatic and coagulation abnormalities [4]. Still the thromboelastograph suggests that children less than 1 year of age with CHD would have a functionally intact and balanced coagulation-fibrinolytic system, but simply at a lower level than healthy children (less hemostatic reserve) [5].
Second, the definition used to determine a normal diagnostic test may matter: Gaussian (mean ± 2 standard deviations), percentile (within 5% to 95%), culturally desirable, risk factor (carrying no additional risk of disease), diagnostic (range of results beyond which target disorders become highly probable), or therapeutic (range of results beyond which treatment does more good than harm) [6]. If one uses one of the two first definitions, the patients identified as abnormal will not necessarily be all at higher risk of developing hemorrhage or thrombosis.
Younger children have higher blood loss and a higher rate of re-exploration for hemorrhage when they undergo an open heart operation [7]. However the high volume of the priming solution compared with the blood volume of the child may well be the sole most important factor to explain this inverse relationship between age and blood loss (ie, more severe dilution of procoagulant factors). Both the Canadian [8] and the Netherlands [9] studies identified: young age (children <1 year or <1 month consisting of 18% and 47.5% of those case series, respectively), central venous catheters (CVC) (32.8% and 63.6%), and CHD (14.6% and 15.2%) as being significant risk markers for the development of deep venous thrombosis (DVT) in children. However, because the flow obstruction produced by a CVC will be more significant in the smaller children, it is unclear whether or not the relative hypercoagulability of the infant is to be incriminated in this higher rate of DVT reported with CVC in neonates [9]. Finally Balling and colleagues [10] reported a 33% rate of thrombus formation in patients who have undergone a Fontan procedure. However, there again, because all thrombi were detected within the right atrium, and because only one was additionally found in the left atrium, local relative blood stasis might have been a more significant causal factor than the increase in factor VIII reported in these patients [11]. Therefore, altogether the clinical relevance of the age-related variations of procoagulant and anticoagulant factors reported here may remain to be clearly demonstrated.
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