1816-8949 1816-8949 S1816-89492020000300185 10.18004/anales/2020.053.03.185 Paraguay 00 12 2020 00 12 2020 53 3 185 186 1 2020 53 2 2 137-44 2 2020 8 78 3 2018 31 248-55 4 2016 33 9 9 816-28