Comparison of Hidden Blood Loss in Biportal Endoscopic Spine Surgery and Open Surgery in the Lumbar Spine: A Retrospective Multicenter Study.

: Biportal endoscopic spine surgery (BESS) is one of the minimally invasive spine surgery techniques. BESS has several advantages, such as better visualization, less muscle injury, early rehabilitation, etc. Due to its clear visualization, delicate intraoperative hemostasis of the bleeding foci, including cancellous bone and small epidural vessels, can be achieved. Therefore, some authors have reported that BESS resulted in less intraoperative visible blood loss (VBL) compared to conventional open surgery. However, it is difficult to analyze the exact amount of intraoperative blood loss because of the continuous normal saline irrigation. In addition, hidden blood loss (HBL) tends to be overlooked, and the amount of HBL might be larger than expected. We aim to calculate the amount of HBL during BESS and to compare our findings with convention open surgery. : We retrospectively obtained the clinical data of patients that underwent lumbar central decompression from July 2021 to June 2024. Patients were divided into two groups: the BESS group that underwent biportal endoscopic lumbar decompression, and the open surgery group that underwent open decompression. Both groups used unilateral laminotomy and bilateral decompression techniques. Total blood loss (TBL) using preoperative and postoperative change in hematocrit (Hct) was measured using Gross's formula and the Nadler equation. Since TBL consists of VBL and HBL, HBL was calculated by subtracting the VBL measured intraoperatively from TBL. : A total of sixty-six patients in the BESS group and seventeen patients in the open surgery group were included in the study. The TBL was 247.16 ± 346.88 mL in the BESS group and 298.71 ± 256.65 mL in the open surgery group, without significant difference (p = 0.569). The calculated HBL values were 149.44 ± 344.08 mL in the BESS group and 171.42 ± 243.93 mL in the open surgery group. The HBL in the BESS group was lower than the HBL in the open surgery group, without significant difference ( = 0.764). : The TBL and HBL during lumbar central decompression were smaller in patients who underwent BESS compared to those who underwent open surgery. While TBL was significantly lower in BESS, HBL did not show statistical significance between the two groups. HBL during BESS should not be neglected, and related hemodynamics should be considered postoperatively.