what is the minimum cost of the entire hospital that involves the sodium, body fluid?
select min(t1.c1) from ( select sum(cost.cost) as c1 from cost where cost.hadm_id in ( select labevents.hadm_id from labevents where labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'sodium, body fluid' ) ) group by cost.hadm_id ) as t1