Largely depends on etiology
If ill appearing, establish rapid IV access, or if needed IO.
Rapid finger stick blood sugar
Point of care pH and electrolytes (iSTAT)
Rapid finger stick blood sugar
Point of care pH and electrolytes (iSTAT)
Avoid IV fluids before doing a trial of oral rehydration therapy in uncomplicated cases of mild to moderate dehydration in children.
Probiotics have NOT been shown to provide any benefit
Nausea and vomiting 
Esophageal stenosis/atresia
Fever and rash
Pyloric stenosis
Abdominal pain 
Intestinal stenosis/atresia
Abdominal pain
Duodenal atresia