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Ann Thorac Surg 2002;73:189-190
© 2002 The Society of Thoracic Surgeons
a Pediatric Cardiac Surgery, Doernbecher Children’s Hospital, Oregon Health and Sciences University, Portland, OR 97201-3098, USA
With this study by Sakamoto and colleagues, the group at Children’s Hospital in Boston has further refined the application of deep hypothermic circulatory arrest (DHCA) for infants undergoing cardiac surgery. In doing so, they have questioned two commonly held dogmas relating to hypothermic cardiopulmonary bypass: (1) that higher hematocrit during cooling might lead to red cell sludging and diminished neurologic function; and (2) that alpha Stat is the preferred acid-base cooling strategy. The results of this study indicate that higher hematocrits (30% versus 20%) during the cooling phase and prior to DHCA result in improved cerebral oxygen availability and correlate with better brain protection. This effect is enhanced with pH Stat cooling, probably because of increased cerebral blood flow.
The driving question behind this work, as well as so many other animal studies over the past decade, is "Is DHCA safe and how do we make it better?" Even in its most unsophisticated form, as it was used throughout the 1970s and 1980s, DHCA enabled surgeons to perform intricate cardiac repairs in tiny infants with outstanding overall results. Perhaps, in some way, the good results during that era with neonatal repair were related to the use of DHCA since in that era, using DHCA greatly limited duration of exposure to cardiopulmonary bypass (CPB). Nevertheless, there was nagging concern, fueled by numerous clinical anecdotal experiences, that neurologic injury was occurring in patients that might in some ways be related to the use of DHCA, especially if exposure was for longer periods of time.
In the 1990s extensive animal research focused on CPB with and without DHCA in an effort to better understand the physiologic implications of each and alter their technical applications. Although it has been argued by some that technical advances now make it possible to avoid DHCA, even in tiny infants, and that DHCA should be avoided at all costs [1, 2], there are no compelling data that this is better for long-term outcome. In fact, there may be some short-term disadvantages with respect to an exacerbated inflammatory syndrome. DHCA continues to play an important role in the strategies available for repair of complex heart disease in neonates and infants [3]. In a recent (unpublished) poll of several prominent congenital heart surgeons in the US and Canada, 2 out of 3 responders claimed that DHCA is still an option that they utilize in appropriate circumstances. There remain several advantages of the use of DHCA including simplification of cannulation in infants with anomalous systemic venous return, simplification of CPB and repair for tiny infants, limitation of duration of exposure of the patient to CPB and an unencumbered operative field for technically difficult operations. In part, the decision to continue using DHCA as a viable option in the twenty first century is predicated on: (1) the lack of significant outcome problems from long-term follow up of patients exposed to DHCA using a conventional DHCA protocols; and (2) the refinement of DHCA application over the past decade from work such as that done by Dr Sakamoto and colleagues.
As opposed to "conventional" protocols in which patients were rapidly cooled using alpha Stat blood gas management for only as long as it took to achieve a nasopharyngeal temperature of 18°C, the application of DHCA today includes several improvements including: (1) preoperative preparation with steroids or aprotinin [4]; (2) pH Stat cooling (especially for recognized high risk patients); (3) hyperoxygenation prior to DHCA[5]; (4) utilization of higher hematocrit during cooling; (5) increased duration of cooling to at least 20 minutes; (6) Intermittent cerebral perfusion during DHCA to limit exposure duration and provide "cerebroplegia" [6]; and (7) the use of modified ultrafiltration (MUF) following DHCA. All of these techniques are supported by laboratory work and have been successfully implemented into the clinical protocols for many centers.
Deep hypothermic circulatory arrest remains a viable and possibly optimal strategy available for the correction of selected congenital heart defects because its application has been improved markedly by research [3] such as that performed by Dr Sakamoto and associates. It remains to be seen how these alterations in management strategies will impact on long term outcome for survivors. Perhaps most important, it is because of DHCA that there are survivors. It is the responsibility of our generation to be innovative, open-minded and flexible as we attempt to improve their quality of life.
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