eComment. Haemolysis in cardiac surgery: a well-known problem with no solution.

Haemolysis in cardiac surgery is a common intractable problem, the consequences of which are still undervalued. Every study on this topic has attracted considerable interest, and the paper of Ricci et al. cannot be overlooked [1]. There are two main causes of haemolysis during cardiac surgery: effect of extracorporeal circulation support devices on patient’s blood (cardiopulmonary bypass, extracorporeal membrane oxygenation, cell salvage, etc.) and red blood cell transfusion. Certainly, mechanically induced haemolysis occupies the leading position in cardiac surgery. Lack of significant effect of transfusion in the above study may be due to small variance in dose or age of transfused red blood cells (RBCs), but it cannot be ignored. It is impossible to completely eliminate haemolysis when using extracorporeal circulation support devices; that depends not only on the device design features, but also on the procedure conditions in each case (left atrial venting flow, suction intensity, venous and arterial cannula position, etc). Increased free haemoglobin level causes dysregulation of vascular tone and tissue oxygenation due to decreased NO bioavailability, increased oxidative stress, and damage to kidney tubules [2]. It is worth noting that application of NO inhalations against haemolysis to treat pulmonary hypertension or right-sided heart failure may not produce the desired effect, because the reaction between free haemoglobin and NO leads to the formation of biologically inert methemoglobin and NO, which may require temporary NO dose adjustment. In moderate haemolysis, its natural body control systems (haptoglobin or haemopexin) may be able to completely neutralize the negative impact of free haemoglobin. However, in case of massive haemolysis their depot rapidly depletes, which predetermines the need for therapeutic interventions. These may be aimed at the elimination of free haemoglobin (haptoglobin involvement or plasmapheresis) or vascular tone regulation recovery (NO donors, endothelin receptor blockers) [3]. However, all these methods have some limitations, and existing experience of their clinical application is either isolated or absent (in vivo experiments only). One can discuss such preventative measures of haemolysis negative consequences in cardiac surgery as creation of extracorporeal circuits or blood storage containers, which are able to inactivate/adsorb free haemoglobin, and thus would allow to eliminate free haemoglobin timely (maintaining haptoglobin pool) or prevent it from entering the body.