  We study quantum corrections for the Schwarzshild black hole by considering
it as a vacuum solution of a 2D dilaton gravity theory obtained by spherical
reduction of 4D gravity coupled with matter. We find perturbatively the vacuum
solution for the standard one-loop effective action in the case of null-dust
matter and in the case of minimally coupled scalar field. The corresponding
state is in both cases 2D Hartle-Hawking vacuum, and we evaluate the
corresponding quantum corrections for the thermodynamical parameters of the
black hole. We also find that the standard effective action does not allow
boundary conditions corresponding to a 4D Hartle-Hawking vacuum state.
