Etomidate is an unique drug used for induction of general anesthesia and sedation. Adrenal cortical inhibition by etomidate has received much attention. However wether the circadian rhythm and pulse secretion pattern of cortisol in children are the same as that in adults is not known. Moreover, the effect of etomidate on circadian rhythm changes and clinical outcomes has never been carefully studied in children undergoing surgery. Our hypothesis is that etomidate can relieve the changes of circadian rhythm of salivary cortisol in children for 24-48 hours，and this does not make clinical outcomes worse postoperatively.