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Eur J Cardiothorac Surg 2007;31:756. doi:10.1016/j.ejcts.2007.01.009
Copyright © 2007, European Association for Cardio-Thoracic Surgery. Published by Elsevier B.V. All rights reserved

Letters to the Editor

Normal temperature and flow: are the ‘physiological’ values so scary?

Antonio F. Corno*

Alder Hey Royal Children Hospital, Eaton Road, Liverpool L12 2AP, UK

Received 5 December 2006; accepted 8 January 2007.

* Corresponding author. Tel.: +44 151 2525713; fax: +44 151 2525643. (Email: Antonio.Corno{at}rlc.nhs.uk).

Key Words: Cardiopulmonary bypass • Congenital heart disease • Pediatric • Perfusion • Surgery

Pouard et al. [1] confirmed the feasibility of normothermic arterial switch, but the Editorial suggested ‘great circumspection’ [2].

Normothermia in pediatric cardiac surgery, used by Lecompte from 1995 [3,4], is not the only characteristic of normothermic cardiopulmonary bypass (CPB) [1]: other factors need to be considered: flow and hematocrit [4].

(a) Flow. The flow generally used for CPB is 2.0–2.4 L/min/m2, far from the ‘physiologic’ values of 3.5–5.0 L/min/m2. The flow is then reduced during the operation to low flow or circulatory arrest. The damages induced by flow reduction (metabolic, endothelial, neurological, myocardial, hematological, vascular, and respiratory derangements) are similar to the damages induced by hypothermia [1,3,4]. In normothermic CPB, pump flow is maintained throughout the procedure at 3.0–3.5 L/min/m2[1,3,4].
(b) Hematocrit. The damages of hemodilution are known from experimental and clinical studies [1,3,4]. In normothermic CPB, hematocrit is maintained above 30% during the procedure, with 40% by the end of CPB [1,3,4].

Temperature, flow, and hematocrit, should be always considered when analyzing papers comparing ‘only’ normothermia versus hypothermia [2].

The ongoing debate on advantages of ‘normothermic, high flow, high hematocrit’ CPB versus conventional techniques is long-lasting in literature and scientific meetings ([2], discussion of ref. [5]).

The arguments against ‘normothermic, high flow, high hematocrit’ CPB are that ‘newborn infants are more vulnerable to the insult of CPB; there is a greater metabolic demand of the developing organs’ [2]. The justification for ‘normothermic, high flow, high hematocrit’ CPB is because infants are more fragile and a more ‘physiological’ type of perfusion, with temperature, flow, and hematocrit closer to normal physiological values, provides less derangements than a perfusion so far from normality [1,3,4].

The solution to find the answer to the question "what is the best technique for pediatric CPB?" is in prospective randomized clinical trials [2].

Unfortunately a prospective randomized clinical trial doesn’t represent a magical solution because of several reasons:

(a) Huge variability among patients with congenital heart defects with regard to their morphology as well as their general condition: a substantial percentage of neonates present with pre-operative cerebral abnormalities.
(b) Standardization of treatment is very difficult: unlike 20 mg tablets, no two surgical procedures are the same.
(c) New surgical techniques are often designed/adopted by technically skilled enthusiasts: the results of prospective randomized studies may not be automatically extended to all surgeons.
(d) Most of comparisons among the different techniques of CPB are obtained in the post-operative period. Minor or major differences in inflammatory markers, neurological status, requirement and duration of inotropic support, stay in ICU, are dependent upon several variables in the patient management, all inter-related and inter-dependent
(e) After having used ‘normothermic, high flow, high hematocrit’ CPB, with smooth and ‘physiologic’ post-operative course, to consider a return to hypothermic techniques is generally seen as undesirable or unethical

The ideal solution, already proposed (discussion of ref. [5]), is that groups with large experience with deep hypothermia and circulatory arrest or low flow perfusion organize a multi-center prospective randomized clinical trial to compare ‘normothermic, high flow, high hematocrit’ CPB with hypothermic techniques.

References

  1. Pouard P, Mauriat P, Ek F, Haydar A, Gioanni S, Laquay N, Vaccaroni L, Vouhé P. Normothermic cardiopulmonary bypass and myocardial cardioplegic protection for neonatal arterial switch operation. Eur J Cardiothorac Surg 2006;30:695-699.[Abstract/Free Full Text]
  2. De Leval MR. Because we can, should we ...?. Eur J Cardiothorac Surg 2006;30:693-694.[Free Full Text]
  3. Corno AF, von Segesser LK. Is hypothermia necessary in pediatric cardiac surgery?. Eur J Cardiothorac Surg 1999;15:110-111.[Free Full Text]
  4. Corno AF. What are the best temperature, flow, and hematocrit levels for pediatric cardiopulmonary bypass?. J Thorac Cardiovasc Surg 2002;124:856-857.[Free Full Text]
  5. Gaynor WJ, Jarvik GP, Bernbaum J, Gerdes M, Wernovsky G, Burnham NB, D’Agostino JA, Zackai E, McDonald-McGinn DM, Nicolson SC, Spray TL, Clancy RR. The relationship of postoperative electrographic seizures to neurodevelopmental outcome at 1 year of age after neonatal and infant cardiac surgery. J Thorac Cardiovasc Surg 2006;131:181-189.[Abstract/Free Full Text]



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Eur. J. Cardiothorac. Surg., April 1, 2007; 31(4): 757 - 757.
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