A 5 year old boy presents with ongoing vomiting and diarrhea. He was discharged the day before following a diagnosis of gastroenteritis and treatment with nasogastric rehydration. His father says that he seems very weak, to the point where he’s been having trouble standing up.

Vitals : HR 130, afebrile. RR 30, sats 98 RA, CRT 3 sec. GCS 15.

Questions:

1. What are the likely causes of weakness in this child with recent gastroenteritis. ?
2. Child had blood tests done and his serum  potassium levels were 2.0 mmol / L . What are the likely explanation of this lab finding ?
3. What further investigation should be performed?
4. How will Potassium be replaced as child is not tolerating well orally?