Postoperative Anemia Predicts Length of Stay for Geriatric Patients Undergoing Minimally Invasive Lumbar Spine Fusion Surgery

Introduction: We hypothesize that postoperative anemia will predict length of stay (LOS) for geriatric patients undergoing minimally invasive (MIS) lumbar spine fusions. Materials and Methods: Patients who underwent MIS lateral and transforaminal lumbar interbody fusion between January 2017 and March 2018 at an academic tertiary care referral center were selected. Eighty-one patients were included. The primary outcome variable was LOS, measured in days. The predictors studied were preoperative hemoglobin (Hgb), postoperative day 1 Hgb, postoperative nadir Hgb, intraoperative Hgb decrement (preoperative Hgb-postoperative day 1 Hgb), perioperative Hgb decrement (preoperative Hgb-postoperative nadir Hgb), age, American Society of Anesthesiologists-Physical Status (ASA-PS) score, volume of perioperative intravenous (IV) fluids (IVFs), and number of levels fused. Simple linear regression and analysis of variance were used for statistical analysis. Results: In the present study, preoperative anemia was not associated with longer LOS (P = .15). Postoperative anemia was associated with longer LOS as both postoperative day 1 Hgb (P = .05*) and postoperative nadir Hgb (P < .0001*) predicted longer LOS. Greater intraoperative Hgb decrement did not predict longer LOS (P = .36); however, greater perioperative Hgb decrement predicted longer LOS (P < .0001*). Older age (P = .01*) and greater number of levels fused (P = .03*) predicted longer LOS; however, a greater ASA-PS classification did not predict longer LOS. Greater IVF administration was associated with longer LOS (P < .0001*). Discussion: Postoperative nadir Hgb (P < .0001*) was more predictive of longer LOS than postoperative day 1 Hgb (P = .05*). There is a perioperative Hgb decrement associated with longer LOS (P < .0001*). Geriatric patients may be more susceptible to the potential contributors to Hgb decrement, including occult bleeding post-op and hemodilution from IVF administration. Conclusion: Postoperative anemia, perioperative decrement in Hgb, older age, greater number of levels fused, and greater total IVFs administered predict longer LOS. Understanding the impact of these factors on LOS is critical as these procedures increasingly move to the outpatient setting.