Blood transfusion is commonly undertaken in critically ill patients; and studies have suggested the use of oxygen extraction ratio (O2ER) as an additional transfusion trigger in critically ill patients. The aim of this study was to establish the relationship between blood transfusion and oxygen extraction ratio in adult patients admitted to the general intensive care unit, using central venous oxygen saturation instead of mixed venous oxygen saturation. Methods: Arterial and central venous blood samples were drawn and a blood gas analysis immediately before commencement of blood transfusion was undertaken. At least 15 min after completion of the transfusion, similar samples were drawn and the blood gas analysis was repeated. The O2ER before and after transfusion was then calculated. Using paired student’s t-test, we checked whether the mean difference between the two O2ERs was statistically significant. Results: We enrolled 58 patients in the study, the mean (±SD) haemoglobin concentration before transfusion was 7.38 g/dl (±1.71). The mean change in haemoglobin concentration following blood transfusion was 2.29 g/dl (±1.18), after transfusing an average of 1.95 (±0.83) units of packed cells. Mean O2ER was 0.27 (±0.11) before, and 0.25 (±0.12) after RBC transfusion. The mean change in O2ER was −0.018 SD ± 0.10 (95% CI, −0.043–0.007; P = 0.15). Linear regression analysis showed no statistically significant relationship between change in haemoglobin concentration and change in O2ER; p-value = 0.12. Discussion: The change in oxygen extraction ratio was not statistically significant following blood transfusion in adult patients admitted to the general ICU at a tertiary teaching hospital. Further studies are required especially in patients with increased pre transfusion O2ER to evaluate the usefulness of this measurement as a possible transfusion trigger.