Sex-Specific Nonlinear Association Between Preoperative Hemoglobin and Intraoperative Oxygen Desaturation in High-Altitude Surgical Patients: A Retrospective Observational Study.

Abstract

High hemoglobin concentration is a compensatory adaptation to high-altitude hypoxia that theoretically increases oxygen-carrying capacity. However, the associated rise in blood viscosity may compromise microcirculatory flow and contribute to intrapulmonary shunting during anesthesia. This study investigates sex-specific associations between preoperative hemoglobin concentrations and intraoperative oxygen desaturation events in surgical patients residing at high altitude. In this retrospective study, we analyzed data from 8010 high-altitude residents undergoing general anesthesia for noncardiothoracic surgery at People's Hospital of Xizang Autonomous Region between January 2020 and October 2024. The dataset comprised preoperative baseline characteristics, information related to surgery and anesthesia. The primary outcome was intraoperative oxygen desaturation, defined as a peripheral oxygen saturation (Spo2 <90% lasting for ≥1 minute) measured by pulse oximetry in patients receiving mechanical ventilation during general anesthesia. Patients were stratified by sex: male (n = 3622) and female (n = 4388). Nonlinear associations were analyzed using multivariable-adjusted restricted cubic splines, and piecewise logistic regression was used to identify hemoglobin thresholds. Nonlinear associations between preoperative hemoglobin concentrations and intraoperative oxygen desaturation were observed in both sexes. For males, piecewise regression identified a statistical inflection point at 20.6 g/dL (adjusted odds ratio [adjOR] per 1 g/dL increase, 1.50; 95% confidence interval [CI], 1.18-1.92; P = .001). For females, the threshold was notably lower at 14.9 g/dL, above which the risk significantly increased (adjOR per 1 g/dL increase, 1.33; 95% CI, 1.13-1.58; P < .001). However, for males, a clinically significant risk increase was observed starting at 18.0 g/dL (adjOR per 1 g/dL increase, 1.23; 95% CI, 1.05-1.45; P = .012). Sensitivity analyses validated these findings across different definitions of desaturation and imputation methods. In high-altitude surgical patients receiving mechanical ventilation during general anesthesia, we identified sex-specific hemoglobin thresholds associated with intraoperative oxygen desaturation. While statistical inflection points occur at higher levels, particularly in males, our data suggest that clinical caution is advised when hemoglobin exceeds 18.0 g/dL in males and 14.9 g/dL in females. These findings underscore the rheological risks of higher hemoglobin concentrations and support the adoption of sex-stratified preoperative assessment protocols to optimize perioperative oxygen delivery.