RESUMO
STUDY OBJECTIVES: To examine the serial time course of perioperative plasma ionized magnesium (iMg(2+)) concentrations and to analyze the plasma iMg(2+) concentrations in children with different body mass who were undergoing open-heart surgery. DESIGN: Randomized, single-blinded study. SETTING: University-affiliated hospital of an academic medical institution. PATIENTS: 38 children undergoing open-heart surgery. INTERVENTIONS: Patients were divided into three groups according to their body mass: Group 1 (n = 12) <10 kg, Group 2 (n = 13) 10 kg to 20 kg, and Group 3 (n = 13) >20 kg. MEASUREMENTS: The relationship of iMg(2+) among the three groups of different body mass were analyzed at five different time intervals during the operation: induction of anesthesia, 5 minutes and 30 minutes after the onset of cardiopulmonary bypass (CPB), the beginning of rewarming, and the end of surgery. MAIN RESULTS: iMg(2+) levels at 5 minutes after onset of CPB in patients weighing less than 20 kg (Groups 1 and 2) differed with those weighing more than 20 kg (Group 3) (p = 0.007 and 0.013). However, there was no difference in the iMg(2+) levels between Groups 1 and 2 (p = 0.993). In addition, iMg(2+) levels at 5 minutes after onset of bypass correlated well (r(2) = 0.66) in children with body mass less than 20 kg. CONCLUSIONS: Low levels of ionized magnesium is an important finding in patients at the onset of CPB, which correlates well with the body mass of patients weighing less than 20 kg, and could be predicted by the regression curve. Based on these findings, hypomagnesemia can be prevented during CPB.