Thanks for placing your query here.
I can appreciate your concerns.
in dengue fever
is mostly due to leakage of fluids out of blood stream into different body compartments & responds usually to intavenous fluids alone.
Some patients do require medicines to support BP.
This critical phase generally last maximum 72 hrs after which the fluid leaked out gradually absorbed back into blood & excreted through kidneys.
Hope I have answered your query.
If you have any further questions I will be happy to help.
Wish him speedy recovery.