Ahmed is a 2 months old boy presented to Pediatric emergency department at Sohag university hospital with persistent vomiting and severe dehydration. His mother told the resident that Ahmed is suffering from projectile vomiting that occurs shortly after feeding since the age of 3weeks .Examination revealed Wt=1.9 kg ,manifestation of severe dehydration and visible gastric perstalisis.
What is the most probable diagnosis?
What is the first step investigation?
What is the management of this case?