oa Southern African Journal of Anaesthesia and Analgesia - Predicting the need for blood during cardiopulmonary bypass : research
<I>Background:</I> Haematocrit (Hct) values <18%-20% during cardiopulmonary bypass (Hct<sub>CPB</sub> ) are potentially unsafe. <br><I>Aims:</I> 1. To predict when bankedblood should be pre-issued. 2. To evaluate the sparing-effect of banked-blood by autologous blood transfusions. <br><I>Methods:</I> An equation for prediction of Hct<sub>CPB</sub> (Hct<sub>pred</sub>), based on weight and pre-operative haemoglobin concentration was used to forecast which patients would develop Hct<sub>CPB</sub> <u><</u> 20%. Perioperative blood and fluid administration were recorded in 80 patients requiring CPB. Blood and fluid administration strived for Hct<sub>CPB</sub> <u>></u>18% on CPB and 33% in the ICU. <br><I>Results:</I> Hct<sub>pred</sub> bias and precision were 2.6% and 13.1%. A Hct<sub>pred</sub> cut-off value of 23% reliably forecast a Hct<sub>CPB</sub> <u><</u> 20% (15 patients with mean Hct<sub>CPB</sub> 16.5%). Despite a 31% false positive rate (FPR), there is emphasis on safety associated with the 23% Hct<sub>pred</sub> cutoff-point. (100% negative predictive value; zero negative likelihood ratio). Applying the same predictive criterion to all blood transfusions performed in the OR, increased positive predictive values from 43% to 63% so that the FPR decreased to 24%. Autologous transfusion comprised 72% of transfused blood and was the only transfusion in 67% of patients. Banked-blood recipients weighed less and had lower pre-operative haemoglobin concentrations, Hct<sub>pred</sub> and Hct<sub>CPB</sub> . They received larger transfusions of which autologous blood formed 46%. <br><I>Conclusions:</I> 1. It is possible to predict which patients will develop potentially low Hct<sub>CPB</sub> . 2. Autologous transfusions result in considerable reduction of banked blood usage.
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