Single centre evaluation of heparin administration by body mass index in elective cardiac surgery

Introduction Heparin has an idiosyncratic anticoagulation response when administered to facilitate cardio-pulmonary bypass (CPB). (1) After an initial loading dose of 300 units per kilogramme (U/Kg) of heparin a number of our elective cardiac surgical patients need additional top-ups to maintain a target activated clotting time (ACT) of at least 420 seconds. This seems more evident in overweight and obese patients. We conducted a service evaluation study to investigate hour heparin administration practices and to understand how they are affected by patients’ BMI in elective cardiac surgery. Methods We undertook a cross-sectional observational study We analysed data on 150 elective cardiac surgical patients. Heparin doses were calculated in units per kilogramme (U/Kg) at 4 stages of surgery: FIRST – initial heparin bolus, PRE – additional top-ups before CPB, PRIME – heparin in the CPB circuit prime, ON- top-ups during CPB. Patients’ body mass index (BMI) was categorised as: LOW 35.1. Results are presented as medians with interquartile range (IQR), percentages and mean percentages with 95% confidence intervals (CI). Results Median FIRST heparin doses (U/Kg) for BMI were: LOW  339 (IQR 58.6) NORMAL  343 (IQR 40.4) OVERWEIGHT 330 (IQR 35.7) OBESE1  308 (IQR 42.4) OBESE2/3  280 (IQR 39.6) The FIRST heparin dose was Depending on the FIRST heparin dose, top-ups required were: If If >300 U/Kg:  PRE 8%,  ON 42%  and both 4% Overall, heparin top-ups were required PRE 13%, ON 49% and both 9% of the whole cohort. As heparin doses were given, the mean percentage contribution at each stage to the total heparin dose received was: FIRST  64.4, 95% CI [62.846, 65.934]. PRE  2.4, 95% CI [1.3219, 3.4581]. PRIME  25.2, 95% CI [24.1707, 26.1293]. ON  8, 95% CI [6.5437, 9.5963]. Depending on the FIRST heparin dose, the median (IQR) total heparin dose (U/Kg) was: If If >300 U/Kg:  500 (IQR 74) Discussion This study has highlighted that in our clinical practice heavier patients received lower loading heparin doses. However, patients who were initially underdosed, went on to require additional heparin doses more frequently than not-underdosed patients. At the end of surgery, underdosed and not-underdosed patients received a similar median total dose of heparin. This study was not designed to identify the reasons our heavier patients tend to have lower heparin loading. This issue warrants further research.