[Neonatal apnea after general anesthesia--effects of intraoperative hyperventilation and serum ionized Ca concentration].

The relationship between neonatal apnea following general anesthesia and serum ionized calcium (Ca2+) concentration was examined in 13 neonates who had received intraoperative hyperventilation. In all cases, preoperative serum Ca2+ concentration was within normal limits. The anesthesia was maintained by nitrous oxide and oxygen. At the end of anesthesia, the incidence of abnormal breathing such as apnea, periodic breathing or subcostal retraction and their activity were investigated. Five minutes after intravenous administration of 2% CaCl2 solution (16 mg.kg-1), the same parameters were compared with the values before CaCl2 administration. As we used only Ca2+ free solution for fluid therapy during operation, serum Ca2+ concentration decreased gradually under general anesthesia, but after CaCl2 administration, it increased and the incidence of abnormal breathing decreased. To determine the relationship between hyperventilation and the incidence of abnormal breathing, the data were analyzed by dividing the patients into two groups based on PaCO2 level, a lower PaCO2 group (intraoperative PaCO2 < 30 mmHg, n = 5) and a higher PaCO2 group (PaCO2 > or = 30 mmHg, n = 8). But there was no significant relationship between them. In conclusion, this study demonstrates that the Ca administration has a favorable effect on respiratory system and motor activity, but we cannot relate the incidence of postoperative abnormal breathing to the degree of hyperventilation.