Fig. 2

a Receiver operating characteristic curves of urine urea (uUrea) and fractional excretion of urea (FEurea). b Receiver operating characteristic curves of urine Na ⁺ (uNa⁺) and fractional excretion of Na ⁺ (FENa⁺) at the time of oliguria recognition to predict cardiac fluid responsiveness. Data are expressed as median (95 % CI)