An apparatus configured for carrying out Continuous Renal Replacement Therapies (CRRT) on patients weighing less than about 20 kg, comprising: a control unit comprising: a blood pump and a plurality of fluid pumps (17, 18, 19) mounted thereon; a controller configured for operating said blood pump and said fluid pumps (17, 18, 19); and an interactive operator control system comprising an operator interface screen operatively connected to said controller, wherein said controller comprises software configured to operate said apparatus in response to operator input selections; and a replaceable panel kit configured to be manually mounted on and removed from said control unit comprising a blood panel; a fluid panel comprising blood and fluid supply tubing, respectively, secured thereon and in operating engagement with said blood pump and said fluid pumps (17, 18, 19), respectively; a filter cartridge panel secured to said blood panel and said fluid panel; and a replaceable filter cartridge mounted thereon, characterized in that, said interactive operator control system includes operator inputs for setting patient weight, blood pump flow rate and fluid pump flow rates; and said controller is configured to calculate and display maximum allowable fluid gain or loss based solely on patient weight settings between zero kg and about 20 kg and trigger an alarm and/or stop operation of said pumps (14, 17, 18, 19) or termination of CRRT in response to patient fluid gain or loss in excess of said maximum allowed fluid gain or loss. a control unit comprising: a blood pump and a plurality of fluid pumps (17, 18, 19) mounted thereon; a controller configured for operating said blood pump and said fluid pumps (17, 18, 19); and an interactive operator control system comprising an operator interface screen operatively connected to said controller, wherein said controller comprises software configured to operate said apparatus in response to operator input selections; and a replaceable panel kit configured to be manually mounted on and removed from said control unit comprising a blood panel; a fluid panel comprising blood and fluid supply tubing, respectively, secured thereon and in operating engagement with said blood pump and said fluid pumps (17, 18, 19), respectively; a filter cartridge panel secured to said blood panel and said fluid panel; and a replaceable filter cartridge mounted thereon, a blood pump and a plurality of fluid pumps (17, 18, 19) mounted thereon; a controller configured for operating said blood pump and said fluid pumps (17, 18, 19); and an interactive operator control system comprising an operator interface screen operatively connected to said controller, wherein said controller comprises software configured to operate said apparatus in response to operator input selections; and a replaceable panel kit configured to be manually mounted on and removed from said control unit comprising a blood panel; a fluid panel comprising blood and fluid supply tubing, respectively, secured thereon and in operating engagement with said blood pump and said fluid pumps (17, 18, 19), respectively; a filter cartridge panel secured to said blood panel and said fluid panel; and a replaceable filter cartridge mounted thereon, a blood panel; a fluid panel comprising blood and fluid supply tubing, respectively, secured thereon and in operating engagement with said blood pump and said fluid pumps (17, 18, 19), respectively; a filter cartridge panel secured to said blood panel and said fluid panel; and a replaceable filter cartridge mounted thereon, characterized in that, said interactive operator control system includes operator inputs for setting patient weight, blood pump flow rate and fluid pump flow rates; and said controller is configured to calculate and display maximum allowable fluid gain or loss based solely on patient weight settings between zero kg and about 20 kg and trigger an alarm and/or stop operation of said pumps (14, 17, 18, 19) or termination of CRRT in response to patient fluid gain or loss in excess of said maximum allowed fluid gain or loss.