Mechanical trauma to the blood can be considered as physical insult presented to the contents of blood, most significantly erythrocytes, but also including platelets and leukocytes. This can result in sublethal damage to cells or even fatally, cell lysis. Mechanical haemolysis is considered a form of haemolytic anaemia and can have a variety of aetiologies. Blood contacting devices are responsible for the majority of mechanical trauma to blood in the field of surgery. In an effort to reduce potential consequences of blood trauma, it is valuable to study the pathomechanisms responsible for causing damage to the blood. The main aspects of this paper are with regards to erythrocytes and their propensity for loss of deformability and increase in aggregation; resulting in their ultimate removal from the vasculature via the spleen. Information regarding trauma to other components of the blood are also discussed where literature is present. This paper compiles the various forms mechanical trauma to blood; devices and mechanisms contributing to sublethal damage and haemolysis; methods of measurement of such damage and methods for protection against it. Research on this topic is growing and its efforts will aid in the reduction of haemolysis from blood contacting devices, and provide better solutions for protection against haemolysis in medical and surgical practices around the world.