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Critical Care Medicine

Dialysis

 

The Continuous Renal Replacement Therapy (CRRT) program began in the Critical Care Unit at the Hospital for Sick Children in approximately 1988.  CRRT was initially in the form of Continuous Arterio Venous Hemofiltration (CAVH) where a vascular access catheter was placed in an artery and a second one in a central vein.  The patient’s mean arterial blood pressure (MAP) was the driving force of blood through an external hemodialysis filter. Special filters were required and the treatment was frequently unsuccessful in very sick hypotensive patients.   In 1990 technological advances allowed for renal replacement therapy to progress using venous access only utilizing a pump to withdraw blood from the patient through one side of a double lumen central venous catheter, drive it through the hemodialysis filter and return the cleansed blood to the patient via the second lumen of the central line.  This obviated the need for arterial access, and improved the success of the treatment.  This form of CRRT was called Continuous Veno Venous Hemofiltration (CVVH).  The machine used was called the Monitral BSM 22 , an old hemodialysis machine.  These circuits were not the “all in one” circuits seen today and required the use of additional pumps to control dialysate flow and fluid removal.  The first patient on the Monitral BSM 22 was a 2.5 kg post operative cardiac patient.

In 1997 Gambro’s Prisma machine was introduced.  This new machine offered flexibility in CRRT therapy with its improved computerized technology and “all in one circuits”.  The delivery of differing modes of therapy Slow Continuous Ultrafiltration (SCUF), Continuous Veno Venous Hemofiltration (CVVH), Continuous Veno Venous Hemodialysis (CVVHD), and Continuous Veno Venous Hemodiafiltration (CVVHDF), could readily be achieved without priming a new circuit.  This allowed for removal of solutes and water through the process of convection (CVVH), the process of diffusion (CVVHD) or both (CVVHDF).

In 2004, Edwards Life Sciences Aquarius machine was introduced to our Critical Care Unit, to overcome significant hemodynamic instability experienced upon initiation of CRRT in patients requiring a blood prime due to the type of AN69 filter used in the circuit, which was associated with bradykinin release and instability.  The blood primed circuit was required  in the less than 11 kg patient due to their small circulating blood volume.  The Aquarius machine offered a safer biocompatible polysulphone membrane, which was better tolerated from a hemodynamic point of view.  Unfortunately, the Aquarius was not well suited to citrate anticoagulation using a CVVHD(F) protocol.

In 2008, a new fleet of 3 Prismaflex machines was Introduced to the ICU.  Prismaflex had an improved user friendly interface with touch screens and clear messaging.  Added safety features were applied to enhance patient safety and prevent inadvertent fluid removal or excess gain.   Also included were polysulphone filters and surface treated AN69 filters, allowing for improved Hemodynamic stability overall. Prismaflex also came with a promise of paediatric software, much needed in the world of paediatric renal replacement therapy, historically intended for patients greater than 20 kg.  The first patient on Prismaflex was a newborn who also required advanced life support via an Extracorporeal Membrane Oxygenation (ECMO) machine.  The Prismaflex worked perfectly in the ECMO circuit while its earlier counterpart had not.  

In 2010 new paediatric software was installed in the Prismaflex machines and the old Prisma and Aquarius machines were retired from service.  Prismaflex with its option of a new smaller membrane (HF 20) now meets the needs of our highest risk and most vulnerable population for CRRT therapy – the neonate.