Effect of low vs. high haemoglobin transfusion trigger on cardiac output in patients undergoing elective vascular surgery: post-hoc analysis of a randomised trial
Department of Anaesthesia and Intensive care Naestved-Slagelse-Ringsted, Slagelse Hospital, Denmark. Copenhagen Trial Unit, Centre for Clinical Intervention Research, Rigshospitalet, Copenhagen, Denmark. Department of Cardiology and Vascular Surgery, Zealand University Hospital Roskilde, Denmark. Department of Anaesthesia, Rigshospitalet, University of Copenhagen, Denmark. Department of Clinical Immunology, Naestved Hospital, Denmark. Department of Anaesthesia, Zealand University Hospital Roskilde, Denmark.
BACKGROUND During vascular surgery, restricted red-cell transfusion reduces frontal lobe oxygen (ScO(2) ) saturation as determined by near-infrared spectroscopy. We evaluated whether inadequate increase in cardiac output (CO) following haemodilution explains reduction in ScO(2) . METHODS This is a post-hoc analysis of data from the Transfusion in Vascular surgery (TV) Trial where patients were randomised on haemoglobin drop below 9.7
g/dL to red-cell transfusion at haemoglobin below 8.0 (low-trigger) vs. 9.7 g/dL (high-trigger). Fluid administration was guided by optimising stroke volume. We compared mean intraoperative levels of CO, haemoglobin, oxygen delivery, and CO at nadir ScO(2) with linear regression adjusted for age, operation type and baseline. Data for forty-six patients randomised before end of surgery were included for analysis. RESULTS The low-trigger resulted in a 7.1% lower mean intraoperative haemoglobin level (mean difference, -0.74 g/dl; P<0.001) and reduced volume of red-cell transfused (median [inter-quartile range], 0 [0-300] vs. 450 ml [300-675]; P<0.001) compared with the high-trigger group. Mean CO during surgery was numerically 7.3% higher in the low-trigger compared with the high-trigger group (mean difference, 0.36 L/min; 95% confidence interval (CI.95), -0.05 to 0.78; P=0.092; n=42). At the nadir ScO(2) -level, CO was 11.9% higher in the low-trigger group (mean difference, 0.58 L/min; CI.95, 0.10 to 1.07; P=0.024). No change in oxygen delivery was detected between trial groups (MD, 1.39 dL(O2) /min; CI.95, -6.16 to 8.93; P=0.721). CONCLUSION Vascular surgical patients exposed to restrictive RBC transfusion elicit the expected increase in CO making it unlikely that their potentially limited cardiac capacity explains the associated ScO(2) decrease.
