I do not know how things are done in Colombia, but here, we have to declare "Minimum Fuel" when it is to be foreseen that, following the present cleared route, fuel on landing will be less than Alternate Fuel plus required final reserve (30 minutes in most cases), and a "Fuel Emergency" ("Mayday, mayday, mayday FUEL") will be declared when fuel on landing is anticipated to be below final reserve.
This declaration is to be made well before the fuel state is reached, not when already flying around on the last fumes.
The rules are good as they are, they just need to be followed.