Acute peritoneal dialysis (APD) is still a useful tool in the critical pediatric patient. Acute kidney failure due to septic shock often requires invasive depuration procedures and although hemofiltration is very effective, not all pediatric Intensive Care Units have the equipment necessary to establish it. Pediatric APD is generally initiated with short dwell times, every hour exchanges and 10-20 ml/kg filling volumes. We present the evolution of two critical patients with kidney failure on APD who benefited from the measurement of dialysate-to-plasma (D/P) ratios for creatinine and urea, and dialysate-to-solution ratio for glucose (Dt/Do) to optimize APD prescription.