78 S . P . Butt et al .: J Extra Corpor Technol 2024 , 56 , 77 – 81
Figure
1 . Illustration of veno-venous bypass for liver transplantation . FV – Femoral Vein , PV – Portal Vein , RIJV – Right Internal Jugular Vein , AV – Axillary Vein .
Figure 2 . Illustration of venovenous bypass circuit . ( a ) Centrifugal pump with access and return line and a heat exchanger added to the return line . ( b ) Bypass loop with gate clamp ( Hoffman ) to control flow through the heat exchanger .
Despite being available and utilized since the 1980s , the routine use of VVB has experienced a decline in LT procedures worldwide . Several factors contribute to this trend , including the high cost of VVB , the associated risks of large-bore line insertion and the bypass procedure itself , the potential for hypothermia , and the availability of alternative techniques [ 3 ].
Over the past two decades , advancements in VVB techniques has taken place , including the emergence of a percutaneous technique as a safer and easier alternative to the traditional surgical cut-down method . This percutaneous approach has shown promise in terms of improved safety and ease of implementation . Furthermore , advancements in extracorporeal technologies including better design , incorporation of heat exchanger devices to prevent hypothermia , and availability of coated circuits for better anticoagulation management has expanded the utilization of VVB in critically ill patients undergoing LT , offering opportunities to enhance patient outcomes [ 1 ].
Methods
We present a modified VVB circuit that incorporates a heat exchanger , illustrated in Figure 1 . This addition enhances the traditional method , which uses a centrifugal pump and a single access and return line , by offering precise temperature control to efficiently warm or cool the patient as needed . Additionally , the inclusion of bubble sensors on both the access and return lines ensures the safety of the circuit by promptly detecting and mitigating any potential risks associated with air embolism . The circuit used is also coated with heparin to reduce the need for anticoagulation and improve biocompatibility .
From a hardware standpoint , we utilize the Rotaflow II System machine ( Getinge , Göteborg , Sweden ) equipped with two bubble detectors and flow probes as illustrated in Figure 2 . These components are affixed to the access and return lines of the circuit . The system offers configurable interventions , such as halting the pump in case air bubbles are detected in either line . Moreover , the console features a flow limits function enabling the establishment of lower and upper alarm thresholds . In addition , we employ the DLP 60000 pressure Display box ( Medtronic , Minneapolis , Minnesota , USA ) to monitor the overall circuit pressure , complete with adjustable lower and upperpressure settings . Furthermore , temperature control is facilitated by the Heater Unit HU 35 ( Getinge , Göteborg , Sweden ).
From a circuit perspective , we employ the Rotaflow pump head coupled with tubing featuring a bioline coating as this enables the utilization of minimal anticoagulation doses during