Patient-specific Cerebral Oxygenation Monitoring as part of an Algorithm to reduce Transfusion during Heart Valve Surgery: A Randomised Controlled Trial

During heart surgery, doctors take measurements to make sure that a patient has enough oxygen for their body to function properly. For example, they check the oxygen supply to the whole body by measuring the amount of oxygen in the blood. When these ‘whole bod’ measures of oxygen show that the body is not getting enough oxygen, doctors try to improve the oxygen supply.

During surgery, doctors also monitor the amount of red cells in the patient’s blood (known as the ‘haematocrit’). Red cells are important because they carry oxygen around the body. Doctors try to keep the haematocrit above a set level because it is assumed that, otherwise, the body will not receive enough oxygen. If a patient’s haematocrit falls below the pre-set level, doctors may give the patient a blood transfusion to try to increase the amount of oxygen available to the body.

These practices are not ideal. Sometimes the haematocrit and the oxygen supply to the body can be normal even when oxygen levels in specific organs and tissues are low. Also we know that transfusing blood to keep the haematocrit above a pre-set level does not always increase the oxygen levels in specific body organs unless they are very low to begin with and although blood transfusions may be beneficial, they can cause harm. Doctors therefore want to avoid unnecessary transfusions where possible.

We think that monitoring oxygen levels in specific organs during surgery would be a better way to decide whether a blood transfusion is needed. Developments in technology mean that we can safely measure the oxygen level in the brain during surgery using sensors placed on the forehead. Using this method, we can adjust the oxygen supply and blood transfusion during surgery to the needs of the individual patient, instead of applying the pre-set level to all patients (as we do now). We believe that the brain is the best organ to monitor because it is most sensitive to decreases in oxygen.

The Pasport study investigated whether monitoring the oxygen level in the brain improves the health of patients after the operation and reduces the number of blood transfusions. We compared this new method with the current method of monitoring the haematocrit and oxygen supply to the whole body to decide when to transfuse blood.

The Pasport protocol paper was published in December 2015.