A girl aged 18 months and 10 kg was transferred from her hospital of origin due to septic shock (maximum noradrenaline 1.5 µg/kg/min, mechanical ventilation 21 days, DIC); APD was started 40 hours after admission due to anuria, increase in creatinine (baseline 0.7 mg/dl, later 2.3 mg/dl) and balance of +2,360 ml. DPA was started on day 2 with 1.36% fluid, 10 ml/kg per hour, 20 minutes, with D/P ratios of urea, creatinine and Dt/Do glucose of 0.91, 0.83 and 0.33, respectively, with effective ultrafiltration between 405 and 700 ml/day. To obtain a negative net balance we had to increase the dialysate concentration to 3.27%. We observed that with a volume of 15 ml/kg and 10 minutes dwell time at 3.27%, the value of the ratios was 0.51, 0.47 and 0.41 (the clearance of substances was not excessive, but we still had sufficient osmotic gradient), so we increased the dwell time to 15 and then to 20 minutes with the following D/P ratios for urea, creatinine and Dt/Do glucose: 0.65, 0.61, 0.41, and 0.75, 0.59, 0.35 respectively, with stabilisation of the upward trend of creatinine at 4 mg/dl. On day 21, cloudy dialysate was observed with low cellularity and increased protein, so we reduced the concentration of the liquid to 2.27% and left it for 4 hours with 15 ml/kg per pass and 4 passes per day (in peritonitis it is recommended to increase the time of permanence and reduce the concentration of the infused solution4). In these circumstances, the values of the D/P ratios of urea, creatinine and Dt/Do glucose were 1.04, 0.85 and 0.14 respectively, so we reduced the duration to 2 hours, 6 daily passes with the same volume and type of liquid, obtaining ratios of 1.01, 0.76 and 0.23 with a decrease in 36 h of creatinine from 4.2 mg/dl to 3.3 mg/dl (renal function of 6.6 ml/min/1.73 m2 by urinary creatinine clearance and 9 ml/min/1.73 m2 by Schwarz formula). On day 27 with 6 daily passes with 1.36% glucose at 15 ml/kg and 2 hours dwell time the ratios were 1.04, 0.92 and 0.13, so we reduced to 90 minutes dwell time and then 60 minutes, being able to increase the number of daily passes to 9, obtaining ratios of 0.98, 0.88 and 0.38 (with 60 minutes dwell time we obtained the same clearance as with 120 minutes dwell time); by being able to make more passes we would improve clearance and ultrafiltration), and a decrease in creatinine from 2.7 to 1.8 mg/dl (renal function of 15 ml/min/1.73 m2 by urinary creatinine clearance and 19 ml/min/1.73 m2 by Schwarz formula), which made it possible to suspend DPA.