Quantification and Predictors of Hemoglobin Drop, Hidden Blood Loss and Irrigation Fluid Retention in Shoulder Arthroscopy.

: Shoulder arthroscopy is a common, minimally invasive surgery, but the resulting postoperative blood loss remains poorly understood. In this study, we quantified the intraoperative and postoperative blood loss, the hemoglobin (Hb) drop, and the effects of irrigation fluid retention, as well as the influence of solutions administered through infusions. : A prospective observational study of 49 patients undergoing arthroscopic rotator cuff tear (RCT) repair was conducted. Their preoperative and postoperative Hb levels were measured, along with the intraoperative and postoperative blood loss. Irrigation fluid retention was analyzed, and multiple regression was used to assess the factors contributing to Hb drops. : The intraoperative blood loss amounted to 36.46 ± 20.34 mL, while the total blood loss reached 791.17 ± 280.96 mL, with 94.64% occurring postoperatively. The postoperative Hb drop (2.06 ± 0.74 g/dL) was significantly greater than the intraoperative Hb drop (0.11 ± 0.06 g/dL) ( < 0.001). An older age ( = 0.02) and male sex ( = 0.025) significantly predicted the postoperative Hb drop, while irrigation fluid retention and administration of crystalloids and colloids had no notable effects. Capsulotomy was associated with a small but significant increase in intraoperative blood loss ( < 0.01). Increased intraoperative blood loss correlated with greater irrigation fluid retention (r = 0.41, adjusted R2 = 0.152, < 0.001). : In shoulder arthroscopy, the postoperative blood loss and Hb drop are significantly greater than the intraoperative blood loss and Hb drop, as well as the fluid gain, emphasizing the need for careful monitoring, especially in high-risk patients. Future studies should investigate the potential impacts of low-molecular-weight heparin on postoperative bleeding after shoulder arthroscopy.