Quantitative venous outflow assessment in reconstructive flaps using indocyanine green angiography: protocol for a systematic review

Background: Venous congestion is a major cause of free flap compromise. Early recognition improves salvage, yet current monitoring relies on clinical inspection and Doppler, which are subjective. Indocyanine green angiography (ICGA) is widely used to assess arterial perfusion. However, its role in evaluating venous outflow is unclear, and published studies use different definitions and measurements. No systematic review has summarized these approaches. Objective: To identify studies that use ICGA for quantitative venous outflow assessment in free flap surgery and determine whether quantitative metrics relate to clinical outcomes. Methods: This protocol follows Preferred Reporting Items for Systematic Review and Meta-analysis Protocols guidelines and is registered in PROSPERO (CRD420251124704). A search will be performed in PubMed, Medline, Scopus and Web of Science. Eligible studies include clinical trials, cohort studies, case series and case reports involving free flap reconstruction where ICGA was used to quantify venous outflow. Two reviewers will screen all records, extract data and assess risk of bias using ROBINS I for observational studies and RoB 2 for randomized trials. Extracted variables include flap type, ICGA system, ICG dose and timing, quantitative measures and reported outcomes. Data will be synthesized descriptively. Discussion: The review will map existing quantitative venous metrics and identify knowledge gaps. Clarifying whether specific ICGA parameters correlate with venous compromise may support standardization of imaging protocols and improve flap monitoring practices.