Serum magnesium levels in the newborn and older child.

In the past, reluctance to determine the serum magnesium level in the newborn infant has been due in part to the relative unreliability of methods hitherto employed (Wacker and Vallee, 1958), and the need for large amounts of blood, particularly where repeat determinations are proposed. In 1964 Rice and Lapara described a rapid, accurate ultramicro method for the determination of ionic magnesium using Mann's Dye. In contrast to the commonly used Titan Yellow method, this method has the advantage of being unaffected by the presence of calcium gluconate (Anast, 1963), making it particularly useful for the determination of the behaviour of magnesium during the course of exchange transfusions (Bajpai, Sugden, Stern, and Denton, 1966). It is established that hypomagnesaemia in the adult can give rise to clinical symptoms (Hanna, Harrison, MacIntyre, and Fraser, 1960). Recent interest in magnesium levels in the newborn infant has been stimulated by the report of hypomagnesaemia associated with convulsions (Davis, Harvey, and Yu, 1965), and neonatal respiratory depression secondary to hypermagnesaemia from maternal magnesium sulphate administration (Fishman, 1965). In a previous report from this laboratory, we have been able to demonstrate a fall in serum Mg+ + levels during the course of exchange transfusion with citrated blood accompanied in extreme cases by electrocardiographic changes (Bajpai et al., 1966). The present report gives our findings in detail using the ultramicro method to determine the Mg+ + levels in the newborn, changes during the