Early Diuretic Initiation Improves Fluid Balance and Recovery After Cardiac Surgery

Introduction: Optimizing fluid management is a cornerstone of critical care following cardiac surgery, involving a complex balance between maintaining adequate filling in the immediate postoperative phase, while minimizing fluid overload. The lack of national guidelines on perioperative diuretic use can lead to delayed diuresis, prolonged fluid imbalance and slower recovery. Following an initial review of loop diuretic prescribing post-cardiac surgery at our institution in the United Kingdom, a revised strategy was devised to promote earlier diuretic initiation. This study aims to reevaluate the impact of this intervention at restoring fluid balance.


Methods: An initial retrospective audit was conducted on patients who underwent cardiac surgery from April-June 2023. Exclusions included congenital/emergency surgeries, extensive aortic repairs and those on diuretics prior to surgery. Data collected included patient demographics, surgery type, timing of diuretic initiation, fluid balance and bodyweight measurements. A targeted intervention was then introduced, aiming for loop diuretic initiation within 48hrs postoperatively. A second review was conducted from April-May 2025.


Results: 83 patients were reviewed in 2023, and 49 in 2025. Initial data showed wide variation in timing of diuretic initiation, with many not initiated until day 4 or later, typically after stepdown from ICU. Early initiation (within days 2-3) and lower early fluid accumulation (0-2000mL by day 2) were associated with faster return to baseline bodyweight. Following intervention, mean day of initiation was significantly reduced (5.14+/-1.56 vs 2.34+/-2.61, p< 0.0001), with over 70% of patients now receiving diuretics within 48hrs whilst still under critical care. This was associated with faster bodyweight normalization (mean 6.3 vs 5.6 days), and more patients returning to baseline weight within 10 days (34.9% vs 38.8%). Although AKI incidence increased (5% vs 12%), all cases resolved before discharge.


Conclusions: Earlier loop diuretic initiation, ideally within 48hrs under intensive care, improves fluid balance and recovery of baseline bodyweight post-cardiac surgery. Further validation may inform national guidelines and support safer, more effective fluid management strategies.