Physiological changes after fluid bolus therapy in cardiac surgery patients: A propensity score matched case-control study.

Objective: Fluid bolus therapy (FBT) is ubiquitous in intensive care units (ICUs) after cardiac surgery. However, its physiological effects remain unclear. Design: Setting: The study was conducted in a multidisciplinary ICU of a tertiary-level academic hospital. Participants: The study included 2,736 patients who underwent Coronary Artery Bypass Grafting and/or heart valve surgery. Main Outcome Measures: Changes in cardiac output (CO) and mean arterial pressure (MAP) during the 60 minutes following FBT. Results: We analysed 3572 matched fluid bolus (FB) episodes. After FBT, but not in control episodes, CO increased within 10 min, with a maximum increase of 0.2 l/min (95%CI 0.1 to 0.2) or 4% above baseline at 40 min (p < 0.0001 vs. controls). CO increased by > 10% from baseline in 60.6% of FBT and 49.1% of control episodes (p < 0.0001). MAP increased by > 10% in 51.7% of FB episodes compared to 53.4% of controls. Finally, FBT was not associated with changes in acid-base status or oxygen delivery. Conclusion: In this quasi-experimental comparative ICU study in cardiac surgery patients, FBT was associated with statistically significant but numerically small increases in CO. Nearly half of FBT failed to induce a positive CO or MAP response.