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J Thorac Cardiovasc Surg 2001;121:597-598
© 2001 The American Association for Thoracic Surgery
Letters to the Editor |
Departments of Surgery and Anesthesiology
Oulu University Hospital
Oulu, Finland
Reply to the Editor:
We would like to express our appreciation for the comments made by Miyamoto and Miyamoto concerning our article in the August 2000 issue of this Journal.
1
We must, however, respectfully disagree with most of their critique. First, the statement concerning the interpretation of our data is arbitrary. We would like to emphasize that in this article two groups of pigs were compared. The study group received lamotrigine and the control group a placebo. Preoperative management, anesthesia, the 75-minute period of hypothermic circulatory arrest at 20°C, and perfusion strategies were similar in all animals and followed a meticulous study protocol. The outcome was examined in terms of hemodynamic, metabolic, neurophysiologic, S-100ß, behavioral, survival, and histopathologic data. Especially considering the overall consistency of the data made obtainable by use of our surviving animal model, the conclusions we made are well justified.
We agree with their statement that "something was wrong in the induction of hypothermia itself besides the protective effects of lamotrigine." It is naturally evident that a circulatory arrest lasting for 75 minutes at 20°C will cause severe brain injury. 2 We would emphasize that the whole idea of using this model was to examine strategies such as lamotrigine, which will improve cerebral protection among animals exposed to a severe global ischemia. In fact, the rate of ischemic insult was determined to be as high as possible while still allowing the animal a possibility to survive. With this approach, it is possible to disentangle the groups by means of outcome measurements, such as histopathology. We would emphasize that this article only demonstrated an improved outcome after lamotrigine treatment compared with the placebo controls. We did not conclude that lamotrigine provides a safe protection for the brain over a 75-minute period of hypothermic circulatory arrest at 20°C.
In addition, Miyamoto and Miyamoto's opinion embodied in the title of the letter is without foundation and disagrees with current literature. 2,3 A 75-minute period of circulatory arrest is much longer than the period regarded to be safe even at a 10°C- to 15°C-level of brain temperature. We are well aware that controversy exists regarding proper stat management. 4 The advantage of pH-stat management is that it allows a more rapid cooling as a result of vasodilatation, but this may also predispose the brain to the steal phenomenon in the absence of autoregulation after the increased embolic load. Therefore, most surgeons are presently using alpha-stat management in operations on the aortic arch. With alpha-stat management, in which blood gases are regulated to remain pH neutral at normal body temperature, resulting in a relatively alkaline environment during hypothermia, cerebral autoregulation is reasonably well preserved, and cerebral blood flow is reduced together with diminishing cerebral oxygen requirements. 3 This is the reason for using alpha-stat management in these experiments.
We very much appreciate Miyamoto and Miyamoto's comments. Unfortunately, we cannot share their opinion regarding the power of pH-stat management without hard data to support it.
12/8/113013
doi:10.1067/mtc.2001.113013
References
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