The Plateau Hemoglobin Paradox: Reversed Effect of Hemoglobin on Surgical Outcomes by Oxygen Saturation Strata at High Altitude

Background: Hemoglobin (Hb) elevation is the hallmark of high-altitude adaptation, yet its effect on surgical outcomes may depend on arterial oxygen saturation (SpO2)--previously uninvestigated. Objectives: To explore whether preoperative Hb effect on postoperative length of stay (LOS) after laparoscopic cholecystectomy (LC) reverses across SpO2 strata. Methods: Retrospective single-center cohort of 612 adults undergoing elective LC (2018-2023) at Qinghai Red Cross Hospital, Xining, China (2260 m). Exposure: preoperative Hb (82-233 g/L) and SpO2 (86%-99%), stratified as low (<93%), mid (93%-95%), high (>=96%). Primary analysis: multivariable linear regression with Hb x SpO2 interaction, adjusted for BMI, age, sex, season. Results: Among 612 patients (65.8% female; mean age 43.5 [11.9] years; mean Hb 151.4 [20.7] g/L; mean SpO2 94.6% [2.3%]), the Hb x SpO2 interaction was significant (beta = -0.0095; P = .009). Hb effect reversed: in SpO2 >=93%, each 1 g/L Hb prolonged LOS by 0.003 days (P = .079); in SpO2 <93%, each 1 g/L reduced LOS by 0.006 days. In mid-SpO2 stratum (n = 251), Hb >=180 g/L had longer LOS (1.88 vs 1.62 days; P = .001; d = 0.54). Five computational robustness analyses confirmed the interaction (leave-one-out: 100% P < .05 across 612 iterations). Conclusions: In this exploratory cohort, we observed an SpO2-dependent reversal of the Hb effect on postoperative LOS, designated the "Plateau Hemoglobin Paradox." Given single-center design and achieved power of 0.754, findings require replication. If replicated, this pattern may inform future perioperative risk stratification at high altitude.