Optimal diuretic dosing strategies following cardiac surgery: a retrospective cohort study

Background: Diuretics are a class of drugs used to treat oedema and fluid overload. Loop diuretics are the most frequently prescribed, with furosemide being the most common in the UK. Furosemide is used following cardiac surgery to re-establish euvolemia following peri-operative fluid administration, however its threshold response is not often appreciated, potentially affecting the diuretic response. There is much deliberation in the literature as to the best way to prescribe diuretics and much of the research relates to prescribing in healthy volunteers, renal failure or heart failure. Evidence suggests that ineffective prescribing can lead to prolonged hospitalisation. We aim to identify trends in prescribing and factors affecting dosing effectiveness. Methods: We undertook a single-centre retrospective cohort study of 101 consecutive post-operative cardiac surgery patients. We collected data from a 4-week period in October 2022 at a large tertiary cardio-thoracic hospital. Baseline demographics, operative details, and diuretic prescription data were collected. The primary outcome measured was the number of dose escalations required in the post-operative period. Secondary outcome measures included hospital length of stay and total diuretic dose amendments. The research purpose of this study was to review furosemide dosage as part of a pilot study, in order to undertake a more in-depth study about the dosing of diuretics in this cohort. Statistical analysis was undertaken using 'R' software. Results: In 101 patients who underwent cardiac surgery 92.1% (N=93) were prescribed postoperative diuretics. The most common starting dose in patients was 40 mg daily, with 76.3% (N=71) receiving this. Of those prescribed diuretics, 49.5% (N=46) required no adjustment to their diuretic dose, while 50.5% (N=47) required at least 1 dose adjustment. Of this group, 42.6% (N=20) patients required 1 change to furosemide prescription, and many needed further subsequent dose escalations to achieve adequate diuresis and fluid balance. All patients that underwent off-pump operations (N=14) required postoperative diuretic, but required fewer dose escalations following those who had cardiopulmonary bypass (CPB). Conclusions: Loop diuretics play a vital role in post-operative fluid management, and establishing euvolemia efficiently in patients can lead to fewer associated complications and a reduced hospital stay. Further research needs to be undertaken reviewing furosemide dosage regimes, in relation to the dose-response curve.