# Perioperative Oxygen Supply-Demand Balance in Patients Undergoing Hemodialysis With Arteriovenous Fistulas: A Retrospective Observational Study

## TL;DR

This study examines oxygen balance in hemodialysis patients during heart surgery, finding that mixed venous saturation levels may not reflect true oxygen balance due to arteriovenous fistulas.

## Contribution

The study provides new insights into interpreting SvO2 in hemodialysis patients with arteriovenous fistulas during cardiac surgery.

## Key findings

- HD patients had a significantly higher cardiac index before surgery compared to non-HD patients.
- SvO2 decreased over time more in non-HD patients, suggesting different oxygen balance dynamics.
- Oxygen delivery index was similar between HD and non-HD patients perioperatively.

## Abstract

Background: Patients with end-stage renal disease on hemodialysis (HD) undergoing cardiac surgery face increased risks. Mixed venous saturation (SvO2) is an important parameter representing the systemic oxygen supply-demand balance. However, interpreting SvO2 in HD patients may be challenging due to arteriovenous fistulas. The literature on these issues is lacking. This study aimed to investigate the change in SvO2 in HD patients by comparing those in non-HD patients perioperatively.

Methodology: From April 1, 2019, to March 31, 2020, 39 patients undergoing cardiac surgery with pulmonary artery catheters, 18 with and 21 without HD, were identified. The cardiac index (CI) and SvO2 were extracted from patient records, and the oxygen delivery index (DO2I) was calculated before surgery (T0), on intensive care unit (ICU) admission (T1), 24 hours (T2), and 48 hours (T3) after ICU admission. A linear mixed effects model was applied for repeated measures analyses.

Results: T0 CI was significantly higher in the HD group (2.5 ± 0.5 vs. 2.0 ± 0.5 L/minute/m2, mean ± SD, P = 0.003) and increased significantly over time in both groups, without an interaction effect (P for interaction = 0.12). T0 SvO2 did not differ between groups (72 ± 10% vs. 72 ± 5%, P = 0.97) and decreased over time, more evidently in the non-HD group (P for interaction = 0.016). DO2I was similar in both groups perioperatively.

Conclusions: SvO2 tended to be higher in the HD group perioperatively. If SvO2 in HD patients is similar to that in non-HD patients, this may mean that the oxygen supply-demand balance is disturbed.