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

## TL;DR

This study finds that fluid bolus therapy after heart surgery leads to small increases in heart output but often fails to significantly improve blood pressure or oxygen delivery.

## Contribution

The study uses propensity score matching to isolate physiological effects of fluid bolus therapy in cardiac surgery patients.

## Key findings

- Fluid bolus therapy increased cardiac output by up to 4% within 40 minutes.
- Nearly half of fluid bolus episodes failed to induce a significant positive response in cardiac output or blood pressure.
- Fluid bolus therapy did not affect acid-base status or oxygen delivery.

## Abstract

Fluid bolus therapy (FBT) is ubiquitous in intensive care units (ICUs) after cardiac surgery. However, its physiological effects remain unclear.

: We performed an electronic health record–based quasi-experimental ICU study after cardiac surgery. We applied propensity score matching and compared the physiological changes after FBT episodes to matched control episodes where despite equivalent physiology no fluid bolus was given.

The study was conducted in a multidisciplinary ICU of a tertiary-level academic hospital.

The study included 2,736 patients who underwent Coronary Artery Bypass Grafting and/or heart valve surgery.

Changes in cardiac output (CO) and mean arterial pressure (MAP) during the 60 minutes following FBT.

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.

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.