[单选] 一个2周大的男孩被父母带到急诊室。 他一生的前几周已经脱水，并且经常呕吐。 父母说，婴儿每次喂奶后都会呕吐，但他总是很饿。 呕吐与进食一致，且颜色不佳。 经检查，婴儿无发热，前font凹陷。 心脏和肺部检查未发现异常。 腹部检查显示可见的蠕动性胃蠕动波，在肝边缘下方上中隔的脐带上方和右侧，有一个2cm坚硬的活动块。 凳子是愈创木脂阴性的。 实验室研究与这种情况的典型发现是一致的。 放置鼻胃管和静脉内管线。 以下哪项是管理中最合适的下一步？A 2-week-old boy is brought to the emergency department by his parents． He has become dehydrated during his first few weeks of life and is vomiting frequently． The parents state that the infant vomits after each feeding but he is always hungry． The emesis is consistent with feedings and nonbilious in Color． On examination， the infant is afebrile and the anterior fontanelle is sunken． Heart and lung examinations reveal no abnormalities． Abdominal examination shows visible gastric peristaltic waves and a 2cm firm， mobile mass above and to the right of the umbilicus in the mid-epigastrium beneath the liver edge． Stool is guaiac-negative． Laboratory studies are consistent with the typical findings of this condition． A nasogastric tube and intravenous line are placed． Which of the following is the most appropriate next step in management？