Introduction & Objective: In spite of the existence of evidence regarding the role of bariatric surgery on body mass index (BMI) reduction, improving apnea-hypopnea index (AHI) and enhancement of oxygen saturation (SPO2), there was no evidence regarding a causal network of these variables. The present study was aimed to investigate the associations using structural equation modeling (SEM). Materials & Methods: A secondary study was conducted using SEM on the aggregate data of the literature. A directed acyclic graph (DAG) was designed and SEM was performed for verification of the hypothesized DAG at P < 0.1. This graph included BMI as an independent variable, percentage of oxygen saturation as a dependent variable, and AHI as a mediating variable. Results: A total of 684 cases were studied. On the average, 12.1 kg/m2 reduction was observed for BMI, 20.0 unit reductions was observed for AHI and 2.1% increase was observed for Mean of SPO2. According to SEM, the effect of reducing the BMI on the reduction of the AHI was positive (effect coefficient = 0.28; that is, a decrease of one unit in the BMI led to a decrease of 0.28 units in the AHI) and the effect of decreasing the AHI was also positive on improving the average percentage of oxygen saturation (effect coefficient = 0.13; i.e., a decrease of one unit in the AHI led to an improvement of 0.13 units in the average percentage of oxygen saturation). Thus, the product of these two paths showed that in the indirect path, each unit reduction in body mass index leads to a 0.04% improvement in the average percentage of oxygen saturation. The coefficient of the direct path was 0.07, which means that the contribution of the mediating path to the total effect is 0.335 (about one third). Conclusions: AHI changes were associated with BMI changes, but the association of SPO2 changes with BMI and AHI changes were not tangible. It seems that the variation of SPO2 changes may be explained by some other variables.