Factors predicting loss and gain of red cell volume in cardiac surgery patients

Abstract

Haemoglobin may be a poor indicator of changes in red cell volume (RCV) because of factors such as haemodilution. This study has been designed to analyse what peri-operative variables may be associated with loss or gain in RCV due to bleeding or transfusion. Prospective observational study. Single centre study based in a regional cardiac surgery centre. Twenty-nine elective adult cardiac surgery patients. Loss and gain of RCV were measured in theatre and for the first 24 h post-operatively. Patient and operative factors analysed were age, sex, height, weight, body surface area (BSA), induction haematocrit (Hct), estimated pre-operative RCV and antiplatelet therapy taken less than 7 days before operation, cardiopulmonary bypass (CPB) time, aortic occlusion time, minimum and maximum CPB temperatures and fluid administered. Age, sex, height, weight, BSA and induction Hct were found to predict red cell transfusion but not RCV loss. The total number of red cells transfused was significantly associated with RCV lost when expressed as a percentage reduction in the estimated pre-operative RCV but not the absolute RCV lost. Pre-operative RCV, as predicted by the variables outlined above, is more important than RCV lost in triggering red cell transfusion.

The ongoing variability in blood transfusion practices in cardiac surgery

“…This enormous range may be attributed partially to a subjectively based instead of an evidence‐based practice and may indicate unnecessary transfusion. Variation in perioperative transfusion practice patterns, however, may also be influenced by differences in patient population among the study centers, including comorbidities as well as other patient‐related factors such as age, body size, 7 or preoperative anemia 10,23,24 . Moreover, preoperative medication with anti‐PLT agents and anticoagulants as well as preoperative transfusion of blood products may impact intra‐ and postoperative transfusion needs 25,26 .…”

Rationalizing blood transfusion in cardiac surgery: preliminary findings with a red cell volume‐based model

“…Previous research has demonstrated that the ability of an individual to tolerate RCV loss is dictated by the preoperative RCV [5]. As gender and weight are major determinates of RCV, we divided preoperative RCV data into male and female categories with three weight‐based subdivisions [4].…”

“…There is currently no convenient and repeatable method for determining RCV. This has led us to develop a transfusion protocol that involved a transfusion threshold derived from body weight (as an estimate of preoperative RCV and therefore the ability to tolerate RCV loss [5]), and a dilution factor to allow the adjustment of postoperative Hb (Table 1). We report preliminary findings of using this ‘RCV transfusion threshold’ as a guideline for the use of RBCs in patients undergoing cardiac surgery.…”

Rationalizing blood transfusion in cardiac surgery: the impact of a red cell volume‐based guideline on blood usage and clinical outcome

“…The most robust formula to date for the calculation of RCV has been provided by the International Council for Standardization in Hematology [10]. Results from previous research have indicated that weight and gender are the most important components of this formula in determining RCV [7]. As such, data from a previous study were divided into male and female categories with three further weight based subdivisions [4].…”

“…Unfortunately, at the time of writing, such a technique does not exist. This has led us to develop a RCV‐based transfusion guideline incorporating both body weight (as a guide to the ability to tolerate RCV loss) and a dilution factor in order to give greater relevance to postoperative Hb (Table 1) [3,4,7,8].…”