# Modifiable risk factors for perioperative hidden blood loss in unilateral biportal endoscopic surgery: a systematic review and meta-analysis

## TL;DR

This study identifies risk factors for hidden blood loss in a type of minimally invasive spine surgery, offering insights to help reduce this complication.

## Contribution

The study is the first to systematically identify modifiable risk factors for hidden blood loss in unilateral biportal endoscopic surgery.

## Key findings

- Higher BMI, longer surgical time, and preoperative hypertension are linked to increased hidden blood loss.
- Elevated preoperative hematocrit levels also correlate with higher hidden blood loss in UBE surgery.
- The findings were confirmed through sensitivity analysis, showing consistent results.

## Abstract

Unilateral biportal endoscopic (UBE) surgery enables precise treatment of lumbar spine pathologies due to its inherent advantages typical of minimally‑invasive endoscopic procedures, including reduced intraoperative blood loss and minimal soft tissue dissection. However, hidden blood loss (HBL) remains a significant challenge in UBE, with limited data regarding its incidence and risk factors.

This study aimed to investigate risk factors associated with HBL in UBE surgery.

Original studies evaluating risk factors for HBL in UBE surgery were systematically searched in MEDLINE, Embase, China National Knowledge Infrastructure, Wanfang Data, and the Cochrane Central Register of Controlled Trials (up to March 2025). The included studies met the quality assessment criteria of the Newcastle‑Ottawa Scale.

Six studies involving 601 patients subjected to lumbar UBE surgery were included. Our meta‑analysis identified that higher body mass index (BMI), prolonged surgical time, preoperative hypertension, and elevated preoperative hematocrit (HCT) levels were significant risk factors for increased HBL in UBE surgery (P <0.05). Sensitivity analysis confirmed the robustness of these findings, with no changes in the significance of the pooled results.

Higher BMI, prolonged surgical time, preoperative hypertension, and elevated preoperative HCT levels are associated with an increased risk of HBL in patients undergoing lumbar UBE surgery. This study serves as a baseline reference for developing public health strategies to mitigate HBL in UBE procedures.