The present invention relates to an apparatus for treating a patient by tidal peritoneal dialysis, the dialysis treatment comprising a succession of cycles each having a fill period, a dwell period and a drain period, the apparatus having at least one cycler suitable for filling the patient's abdominal cavity with a defined admission volume of fresh dialysis solution until attainment of a defined patient volume in the fill period and for draining spent dialysis solution from the patient's abdominal cavity until attainment of a defined tidal discharge target in the drain period, the apparatus further having at least one processor which drives the cycler in at least one operating mode such that the drain period is ended before the tidal discharge target is attained, so that an allowable residual volume remains in the abdominal cavity and then a fill period is commenced, and the fill period is implemented in such a way that when the fill period has finished the fill volume of the patient is at an allowable patient volume which is above the defined patient volume.
