1. Field of the Invention
The present invention relates to a water-removal control system for dialysis devices and, more particularly, to a water-removal control system capable of recalculating and displaying a planned finish time of dialysis treatment by changing at least one of preset values of a planned water-removing volume and a water-removing rate when there is the necessity of changing a predetermined finish time of dialysis treatment for some reasons or other during dialysis.
2. Description of the Prior Art
Dialysis devices have been used widely to perform dialysis treatment for patients with chronic renal failure. Such dialysis devices are generally composed of a dialyzer, a blood line, a dialysate line, a blood pump, a water-removal pump, and a water-removal control system. The water-removal control system generally comprises a volume-setting means for setting a volume of water to be removed, a rate-setting means for setting a water-removing rate, a control means for controlling water-removing procedure on the basis of a set value of the water-removing rate set by the rate-setting means. The control means is so designed as to calculate a necessary time for dialysis from the set volume to water to be removed and the set value of the water-removing rate, and determine a finish time of dialysis treatment, i.e., a time at which the dialysis treatment has been finished, from the necessary time and the actual time. Generally, the control means is so designed as to have the ability to change the volume of water to be removed and the water-removing rate even in the dialysis treatment.
High performance dialysis devices have recently been developed and make it possible to remove a large volume of water from the blood. However, there is such a fear that the patient's life is in danger because of improper control of water removal which causes excessive or insufficient water removal. Thus, there is an increasing demand for a water-removal control system for dialysis devices that ensures correct and safe control of water removal.
To meet such a demand, a few dialysis devices with a ultrafiltration control system have been proposed, for example, in Japanese Utility Model publication JP-B- 6-11001 and Japanese Patent JP-A - 6-14994.
The former discloses a dialysis device comprising a volume-setting means for setting a planned volume of water to be filtered, a rate-setting means for setting a filtering-rate, a control unit for controlling ultrafiltration procedure on the basis of the filtering rate determined by the rate-setting means, the control unit being so designed that it allows at least one of the filtration volume and filtering-rate to be changed during dialysis treatment, the control unit being adapted to calculate the remaining time of dialysis, by using the planned filtration volume, the filtering-rate, and the volume of water filtered by that time, and to display the result. If the filtration volume or filtering-rate is changed during dialysis, the control unit recalculates remaining time of dialysis from the changed value and displays the result.
The latter, JP-A- 6-14994, discloses a water-removal calculating system for dialysis device, including means for setting a planned volume of water to be removed, a planned finish time of dialysis treatment and a current time as data for control of water-removal, and a means for calculating the required time for dialysis treatment from the data, from which the water-removing rate at the time of start of dialysis is calculated automatically. If the dialysis treatment is delayed for some reasons or other, the water-removing rate is automatically recalculated from the remaining time of dialysis treatment and the remaining volume of water to be removed, to eliminate the delay of dialysis treatment, and then reset the water-removing rate to the calculated new value.
However, the dialysis device of JP-B- 6-11001 does not display the finish time of dialysis treatment, but the remaining time of dialysis treatment, so that the operators are liable to make a wrong judgement carelessly on the finish time of dialysis treatment. If it becomes difficult to finish the dialysis treatment within the initially planned time for some reasons or other, there is the necessity of finishing the dialysis treatment within a time shorter than the initially planned finish time. In such a case, the dialysis treatments often bring to an end simultaneously, particularly, when many patients are treated at the same time, so that the operators are pressed by work because of after-treatment and preparation for the next treatments. Accordingly, the operators would make a mistake in calculation when setting the planned volume of water to be removed from the blood or ultrafiltration rate.
Since the water-removal calculating system of JP-A- 6-14994 is so designed as to reset the water-removing rate to finish the dialysis treatment at the initially determined time, the water-removing rate becomes too fast, causing excess water-removal. This problem may be overcome by setting upper limits to the water-removing rate, but it requires recalculation of the water-removing rate every when the water-removing rate exceeds the limit.