Clinical and Chemical Outcomes Following Cardiac Surgery: The Post-Operative Effects of Modified Ultrafiltration (On-line MUF) and Off-line (MUF)

Current practice in cardiac surgery requiring cardiopulmonary bypass (CPB) dictates the salvage of the residual circuit volume at the end of the procedure into an autologous recovery system. This system uses the centrifugation method (CF) to separate whole blood into red blood cells (RBCs) and plasma components (Sutton et al, 1993). The RBCs are then washed with normal saline and re-infused into the patient as needed while the plasma components are discarded.

While this technique produces a product with a high haemoglobin (Hb), the main disadvantage of this process is the loss of plasma protein and clotting factors (Samolyk et al, 2005).

The Modified Ultrafitration (MUF) is a standard of care technique that was originally used on pediatric patients undergoing cardiac surgery with CPB. Following CPB while the aorta is still cannulated, MUF uses an inline hemofilter to concentrate the patients total blood volume thereby increasing Hb, plasma proteins, systemic blood pressure, and cardiac index while decreasing cytokines and post-operative bleeding (Kiziltepe et al. 2001).

According to a task-force on evidence based surgery (the Society of Thoracic Surgeons and the Society of Cardiovascular Anesthesia) the use of modified ultrafiltration (online-MUF) is indicated for blood conservation and reduction of post-operative blood loss in adult cardiac operations using cardiopulmonary bypass (CPB) (Ferraris et al 2011). Moreover, Luciani et al. 2001, showed significantly lower levels of GI, neurologic and cardiac complications in patients who underwent on-line MUF following cardiac surgery as compared to those who did not. They also demonstrated a significantly lower mortality at 30 days follow-up in patients receiving online MUF as compared to control. Boodhwani et al. (2006) demonstrated that the use of online MUF was associated with a 0.72 unit reduction in blood transfused and a reduction of post-operative loss. The disadvantages to this technique are the time required (10-15 min), delays protamine administration, and the requirement of anaesthesia cooperation for pressure management. According to the Proceedings of the American Society of Extracorporeal Technology International Conf. March 9, 2013, online MUF works best and is recommended for smaller patients 75 kg or less because the effect of concentration of the blood volume is greater in smaller patients as compared to larger patients. In house data collected by our Department of Clinical Perfusion at the Royal University Hospital has demonstrated that 70% of the smaller patients undergoing cardiac surgery (mainly women) receive allogeneic transfusion peri- and post-operatively.

Off-line MUFF, another standard of care technique, is used after separation from CPB and decannulation. This technique uses a hemofilter to concentrate the residual CPB volume to produce a product which is more analogous to whole blood as compared to that processed by the CF method. Recently, our research group has shown that after 12-hours post-operatively patients' biochemical (total protein and albumin) and clinical parameters (vasoactive inotrope score and fluid balance) were significantly improved when patients' residual CPB volume underwent multiple-pass hemofiltration as compared to the CF (McNair et al. (2013), Journal of Cardiothoracic and Vascular Anaesthesia, In Press). Recently, it has been demonstrated that following cardiac surgery, the post-operative use of vasoactive inotropes is decreased when the residual CPB volume is processed by the offline MUF method as compared to the CF method (Coli et al 2012; McNair et al. (2013), Journal of Cardiothoracic and Vascular Anaesthesia, In Press). The disadvantages of on-line MUFF are the possible entrainment of air into the arterial line and prolonged time for protamine administration. The disadvantages of off-line MUFF are inadequate clearance of heparin by the hemofilter and prolonged processing time.