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J Thorac Cardiovasc Surg 2002;124:856-857
© 2002 The American Association for Thoracic Surgery

Letters to the Editor

What are the best temperature, flow, and hematocrit levels for pediatric cardiopulmonary bypass?

Cardiovascular Surgery, Centre Hospitalier Universitaire Vaudois, (CHUV), 46 rue du Bugnon, CH-1011, Lausanne, Switzerland

To the Editor:

I read with great pleasure the letter by Durandy, Hulin, and Lecompte ¹ on normothermic cardiopulmonary bypass in pediatric surgery, as well as the reply by Jonas, Newburger, and Bellinger. ²

I spent 1 year with Durandy and Lecompte in Paris in 1995, at the beginning of their experience with normothermic cardiopulmonary bypass, and witnessed the extremely smooth and "physiologic" postoperative course of more than 300 consecutive children with congenital heart defects. Most of them had very complicated anatomy and intracardiac repair, and almost all of them were extubated very early, without the need for inotropic support. I repeatedly suggested that Durandy and Lecompte report their extraordinary experience. Their reason for refusing to report their data at that time was the need for more substantial background.

I then decided to follow their methods of cardiopulmonary bypass, and the initial experience has been already reported. ^3,4 Therefore, I viewed the publication of their letter with a great sense of relief, because the feasibility and the advantages of normothermic cardiopulmonary bypass have been now supported by their experience with 1600 congenital cases.

To further support the message given in the letter, I feel obliged to extend the information provided by Durandy, Hulin, and Lecompte. In their letter they discussed only the problem of temperature, although there are at least other three factors used in their practice of cardiopulmonary bypass that contributed to their good results: flow, hematocrit, and leukocyte depletion.

1. Flow. The flow generally used for cardiopulmonary bypass is 2.0 to 2.4 L · m^-2 · min^-1 or 100 to 120 mL · kg^-1 min^-1. Even if this flow rate is accepted as the gold standard for adequate systemic perfusion, and it is called "full flow," it is far from the physiologic value of 3.5 to 5.0 L · m^-2 · min^-1. In most hospitals the so-called "full flow" is reduced during the central part of the procedure to a low flow or to circulatory arrest. The types of damage induced by flow reduction (metabolic derangement; endothelial lesions; vascular, myocardial, neurologic, hematologic, and respiratory impairment) are not much different from those induced by temperature reduction. ^3,4 In fact, I learned from the Paris group to perfuse the children with a flow of 3.0 to 3.5 L · m^-2 · min^-1, arbitrarily called "high flow."
   
2. Hematocrit. The negative consequences of a systemic perfusion with low hematocrit, widely know for a long time, ^3,4 are now acknowledged even by Jonas. After years suggesting that perfusion with high hemodilution (hematocrit value around 20%) should be used, his group ⁵ is now providing evidence of better neurologic protection with a hematocrit value of 30%. From the Paris group I learned to maintain the hematocrit value at least at 30% during cardiopulmonary bypass.
   
3. Leukocyte depletion. The role of leukocyte activation as the main cause of the postoperative inflammatory syndrome, frequently observed in the pediatric population, is generally well known, even if leukocyte depletion is not yet used globally.
   

In their reply to the letter, Jonas, Newburger, and Bellinger ² suggested two main objections: a small margin of safety in the event of equipment failure and inadequate surgical exposure.

1. Small margin of safety. The incidence of "equipment failure" on cardiopulmonary bypass reported in the literature is between 1 every 1,000 or 10,000 procedures. Even if we consider these figure as an underestimation of the reality, this percentage is much lower than the percentage of children with low cardiac output, need for extensive inotropic and respiratory support, neurologic complications, and the related mortality and morbidity reported even in the best centers after "conventional" cardiopulmonary bypass.
   
2. Inadequate surgical exposure. The good results of both the experience of the Paris group ¹ with neonates and infants with cyanotic congenital heart defects (tetralogy of Fallot, transposition of the great arteries) and our more limited personal experience including infants with total anomalous pulmonary venous connection ^3,4 demonstrate the feasibility of the technique. Of course, it is necessary to have adequate venous drainage, perfect surgical exposure, and a surgeon ready to accept some discomfort for himself (or herself) rather than for the patients.
   

References

1. Durandy Y, Hulin S, Lecompte Y. Normothermic cardiopulmonary bypass in pediatric surgery [letter]. J Thorac Cardiovasc Surg. 2002;123:194[Free Full Text]
   
2. Jonas RA, Newburger JW, Bellinger DC. Reply. J Thorac Cardiovasc Surg. 2002;123:194.
   
3. Corno AF, von Segesser LK. Is hypothermia necessary in pediatric cardiac surgery? Eur J Cardiothorac Surg. 1999;15:110-1.[Free Full Text]
   
4. Corno AF, von Segesser LK. Cardiopulmonary bypass: Do we know the optimal temperature and flow? Cardiovasc Eng. 2000;5:175-8.
   
5. Sakamoto T, Zurakowski D, Duebener LF, Hatsuoka S, Lidov HGW, Holmes GL, et al. Combination of alpha-stat strategy and hemodilution exacerbates neurologic injury in a survival piglet model with deep hypothermic circulatory arrest. Ann Thorac Surg. 2002;73:180-9.[Abstract/Free Full Text]
   

This article has been cited by other articles:

				A. F. Corno Systemic venous drainage: can we help Newton? Eur. J. Cardiothorac. Surg., June 1, 2007; 31(6): 1044 - 1051. [Abstract] [Full Text] [PDF]

				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]

				A. F. Corno A lost opportunity. J. Thorac. Cardiovasc. Surg., June 1, 2004; 127(6): 1857 - 1858. [Full Text] [PDF]

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