Abstract
Haemodilution is a technique used to reduce perioperative homologous blood transfusions. Haemodilution is a poorly investigated technique in veterinary medicine. This article reviews haemodilution as a potential technique to reduce perioperative homologous blood transfusions. The history of haemodilution is briefly reviewed followed by the mathematical basis to haemodilution. The issue of critical oxygen delivery and its implications for haemodilution are discussed. The effects of haemodilution on the patient, including the effects on oxygen transport, blood flow and coagulation are discussed as well as the use of colloids, fluids and blood components in haemodilution. The success and failure of haemodilution in human clinical trials and experimental evidence is discussed. Some guidelines are given for the use of haemodilution in small animal patients in the perioperative setting. It appears in all likelihood that haemodilution has a limited application in cats and other small patients. Haemodilution is most beneficial when the initial haematocrit is high, a low haemodiluted haematocrit is achieved, the patients circulating volume is large and a large amount of blood was lost. It is important to avoid haemoconcentration during surgery as this increases red blood cell loss. Haemodilution is not a substitute for poor surgical technique and inadequate haemostasis intra-operatively. Intravascular volume should be maintained throughout the procedure.
Highlights
During surgery blood is lost from the body and fluids are infused to maintain normovolaemia
If the same patient had a haematocrit of 25 % and the same blood loss occurred, a total of 250 m of red blood cells were lost, representing a saving of 200 m of red blood cells[45]. This has been the traditional impetus behind acute normovolaemic haemodilution (ANH)
If the haematocrit is less than 30 % it is not possible to save an appreciable amount of red blood cells even if the patient is haemodiluted to 15 %13
Summary
If the same patient had a haematocrit of 25 % and the same blood loss occurred, a total of 250 m of red blood cells were lost, representing a saving of 200 m of red blood cells[45] This has been the traditional impetus behind acute normovolaemic haemodilution (ANH). The amount of blood saved by haemodilution is dependent on the patient’s circulating blood volume, initial haematocrit, the diluted haematocrit, the allogeneic transfusion trigger point and surgical blood loss[13,21,22,52]. Feldman et al showed, that the same patient required the removal of 2250 m of blood in order to achieve a maximum benefit from haemodilution[13] This far exceeds the blood loss occurring during the procedure. If the haematocrit is less than 30 % it is not possible to save an appreciable amount of red blood cells even if the patient is haemodiluted to 15 %13
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