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Acid-base and electrolyte changes in infants undergoing profound hypothermia for surgical correction of congenital heart defects

Summary

Acid-base and electrolyte changes are reported in 11 infants undergoing profound hypothermia for cardiac surgery by the technique of initial surface cooling followed by further bypass cooling and rewarming. Seven patients (group 1) underwent initial surface cooling to a mean oesophageal temperature of 26.6° C and four (group 2) to a mean oesophageal temperature of 32° C.

During initial surface cooling, Pco2 was maintained close to 40 mm Hg by the addition of CO2 to the inspired gas mixture and there were no significant mean changes in pH or calculated base excess values in either group. The most significant electrolyte change was the decrease in plasma K+ in group 1. The possible relationship between the decrease in plasma K+ and the incidence of ventricular fibrillation was discussed. Although a slight but not statistically significant decrease in plasma total calcium was observed, the physiologically active ionic calcium level remained completely within the normal range. There were no changes in plasma Na+ or magnesium during surface cooling in either group.

During bypass cooling any potential changes which might have resulted from the further drop in temperature were modified or overshadowed by the effects of the composition of the priming solution. Five per cent CO2 was found to be insufficient to maintain Pco2 levels during cooling bypass and at least 10 per cent CO2 is now recommended.

Administration of NaHCO3 to correct the metabolic acidosis observed early during bypass rewarming resulted in post-operative metabolic alkalosis. Correction of the acidosis was found to occur spontaneously by the time of chest closure, hence treatment is usually unnecessary.

Calcium ion activity is maintained during bypass and in the post-operative period by the addition of 2 ml of 10 per cent CaCl2 to each unit of heparinized blood used in the prime or as replacement during bypass.

Plasma K+ concentrations were normal during bypass cooling and early rewarming but decreased to low normal values by the time of chest closure. They remained low in both groups during the first 24 post-operative hours, half the values being in the hypokalaemic range despite the administration of potassium (2 mEq/kg/24 h). The post-operative dosage of potassium in these infants should be increased to 3-4 mEq/kg/24 h for 1 or 2 days depending on adequacy of renal function and plasma potassium levels.

The plasma magnesium concentrations were maintained in the normal range during bypass in both groups. Nevertheless, the patients in group 1 were hypomagnesaemic postoperatively.

A magnesium supplement administered postoperatively to the patients of group 2 in a dose of 1 mEq/kg/24 h was sufficient to maintain plasma magnesium levels in the high normal range.

Résumé

Nous avons fait ľétude des changements acide-base et électrolytiques chez 11 enfants soumis à une hypothermie profonde pour chirurgie cardiaque et, cela, avec la technique du refroidissement périphérique ďabord et, ensuite, ďun autre refroidissement par la circulation extracorporelle et puis, le réchauffement. Sept malades (groupe 1) ont subi un refroidissement périphérique de départ jusqu’à une température œsophagienne moyenne de 26.6° C et quatre autres malades (groupe 2) à une température œsophagienne moyenne de 32° C.

Durant la phase initiale de refroidissement périphérique, nous avons maintenu la Pco2 près de 40 mmHg en ajoutant du CO2 à ľair inspiré et nous n’avons pas observé de changement du pH ni de ľexcès de base dans ľun et ľautre des groupes. Le changement le plus marqué a été celui de la diminution du potassium plasmatique dans le groupe 1. Nous avons discuté le lien éventuel entre cette diminution du potassium plasmatique et la fréquence de la fibrillation ventriculaire. Bien que nous ayons observé une légère mais statistiquement non significative diminution du calcium total plasmatique, le taux de calcium ionisé et physiologiquement actif est demeuré dans les limites de la normale.

Le taux du sodium et du magnésium plasmatiques est demeuré inchangé durant le refroidissement périphérique dans les deux groupes.

Durant le refroidissement de la circulation extracorporelle, tous les changements éventuels qui auraient pu résulter ďune chute additionnelle de température étaient modifiés ou masqués par les effets de la solution ďamorce. Nous avons observé que 5 pour cent de CO2 n’était pas suffisant pour maintenir le taux de CO2 durant le refroidissement par la circulation extracorporelle et, maintenant, nous recommandons au moins 10 pour cent.

Ľadministration de bicarbonate de sodium pour corriger ľacidose remarquée précocement durant la circulation extracorporelle réchauffante a entraîné une alcalose métabolique au cours des suites opératoires. Nous avons noté que ľacidose se corrige spontanément durant la fermeture du thorax; le traitement devient alors superflu.

Ľéquilibre de ľion calcium est surveillé durant la circulation extracorporelle et au cours des suites opératoires; nous ajoutons deux ml de CaCl2 à 10 pour cent chaque unité de sang hépariné utilisée pour ľamorce ou pour le traitement durant la circulation extracorporelle.

Les concentrations de potassium plasmatique sont demeurées normales durant la circulation extracorporelle de refroidissement et au début de réchauffement, mais elles ont diminué à des données normales basses au moment de la fermeture du thorax. Elles sont demeurées basses, pour les deux groupes, durant les premières 24 heures post opératoires; la moitié ďentre elles étant de ľordre de ľhypo kalémie malgré ľadministration de potassium (2 mEq/Kg/24 hres). Nous conseillons ďaugmenter le taux de potassium post-opératoire chez ces enfants à 3–4 mEq/Kg/24 h durant 1–2 jours selon le fonctionnement adéquat des reins et les taux de potassium plasmatique.

Nous avons maintenu ľéquilibre des taux de magnésium plasmatique près de la normale durant la circulation extracorporelle dans les deux groupes. Néanmoins, au cours des suites opératoires, les malades du groupe 1 étaient hypomagnésiumhémiques.

Au cours des suites opératoires des malades du groupe 2, nous avons donné un supplément de magnésium à la dose de 1 mEq/kg/24 hres et cela a été suffisant pour maintenir les taux de magnésium plasmatique dans la partie haute de la normale.

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Correspondence to A. E. Johnston or I. C. Radde or D. J. Steward or J. Taylor.

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Johnston, A.E., Radde, I.C., Steward, D.J. et al. Acid-base and electrolyte changes in infants undergoing profound hypothermia for surgical correction of congenital heart defects. Can. Anaesth. Soc. J. 21, 23–45 (1974). https://doi.org/10.1007/BF03004577

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Keywords

  • CANADIAN Anaesthetist
  • Nous Avons
  • Surface Cool
  • Priming Solution
  • Chest Closure