Effect of Irrigation Pressure on Postoperative Complications and Surgical Field Clarity in Unilateral Biportal Endoscopic Surgery

Background: Unilateral biportal endoscopy (UBE) is a minimally invasive spine surgery technique that has been increasingly used for lumbar disc herniation, spinal stenosis, and other degenerative conditions. Irrigation fluid is essential in UBE to maintain the surgical space and control bleeding. However, the pressure of irrigation fluid may be associated with complications such as neck pain, seizures, and increased intracranial pressure. The height of the fluid bag and the direction of the surgical incision are two controllable factors that may influence actual irrigation pressure and surgical field clarity, but prospective clinical evidence is lacking.

Objective: This study aims to investigate the effects of different fluid bag heights (0.9 m vs. 1.0 m) and incision directions (horizontal vs. vertical) on irrigation pressure, surgical field clarity, blood loss, and early postoperative pain and functional recovery in patients undergoing UBE surgery. Additionally, disc tissue collected during surgery will be used to explore the relationship between disc degeneration and factors such as sex, age, mechanical stress, and injury.

Design: This is a single-center, prospective, randomized controlled trial. Approximately 80 patients scheduled for UBE surgery at the First Affiliated Hospital of Kunming Medical University will be enrolled. Patients will be randomly assigned to one of four groups: (1) 0.9 m fluid bag height + horizontal incision; (2) 0.9 m fluid bag height + vertical incision; (3) 1.0 m fluid bag height + horizontal incision; (4) 1.0 m fluid bag height + vertical incision. Intraoperative irrigation pressure around the dura will be continuously measured. Surgical field clarity, blood loss, and early postoperative outcomes will be recorded. Patients will be followed for at least 6 months.

Inclusion criteria

• Age >= 18 years and < 75 years.
• Patients scheduled for unilateral biportal endoscopic (UBE) surgery for lumbar degenerative disease at the First Affiliated Hospital of Kunming Medical University between February 2026 and December 2027.
• Follow-up duration > 6 months.
• Complete clinical and follow-up data available.
• Voluntary participation and signed informed consent.

Exclusion criteria

• History of tuberculosis, infection, tumor, or trauma.
• Severe cardiac, hepatic, or renal insufficiency.
• History of chronic lung disease, liver disease, HIV infection, diabetes, or renal insufficiency.
• Psychiatric disorders or inability to comply with follow-up.
• Severe osteoporosis.
• Pregnant or lactating women.