The effect of hemorrhage on the oxygen supply

Several factors contribute to decreased oxygen supply to the tissues following haemorrhage. These are summarised in the following equation:

Cardiac Output X Hemeglobin X O2 Saturation in Blood = O2 supply to tissues

When significant blood loss occurs, the fall in oxygen carrying capacity of blood together with the reduction in blood volume cause a fall in oxygen delivery. If intravenous therapy is started to maintain normovolemia, a normal or increased cardiac output may occur which enables an adequate oxygen continue. Replacement of blood loss with crystalloids or colloids also results in dilution of the blood components or hemodilution. Initially this reduces the viscosity of blood, which improves capillary blood flow and cardiac output, enhancing the supply of oxygen to the tissues. Therefore the key objective is to ensure normovolemia at all times during the course of a surgical procedure. When the Hb falls below 7-8g/dl the cardiac output can no longer compensate for the anemia and blood transfusion is usually necessary.

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Mr. Jan B. Wade
Blood Management Consultant
Enhance Outcomes - Control Cost
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