During many types of heart surgery, the blood, which would normally pass through your heart, is passed through a heart-lung machine. The heart-lung machine does the work of the heart and lungs by keeping the blood oxygenated and flowing around your body, whilst the heart is stopped and lungs are deflated. This machine makes it easier for the surgeon to operate because the heart and lungs are not moving and there is no blood in the heart. However, using the heart-lung machine increases the chances of having a complication after surgery. These complications can impede recovery and increase the length of hospital stay.

The purpose of the COMICS study is to compare the use of conventional heart-lung machines with miniaturised heart-lung machines. Miniaturised heart-lung machines have been developed by several manufacturers with the aim of reducing the risk of having a complication due to from using a heart-lung machine.

This study will compare the incidence of a number of specified complications in patients having their operation with using the conventional heart and lung machine and patients having their operation using the miniaturised heart and lung machine. The complications that the miniaturised heart-lung machine aims to avoid include heart attack, stroke, major bleeding and blood transfusion, and kidney injury. The study will also look at the amount of blood products transfused in both groups, the length of hospital stay and the overall resources used to treat patients during their hospital stay.