Background: Pain management with the use of sedatives and analgesics has several advantages and few complications or side effects. Objectives: In this study, we planned to evaluate the effects of pain control on oxygen saturation independent of other factors, such previous cardio-pulmonary conditions or respiratory rate. Patients and Methods: Sixty-seven adult patients with direct trauma to extremities, who were referred to Imam Hossein Educational Hospital emergency room were enrolled in this study. Exclusion criteria were trauma to parts of the body other than extremities, and comorbidity with cardiovascular, pulmonary, or other disorders. Pain was evaluated using a numerical rating scale and scored between 0-10. Patients’ respiratory rates (RR) were recorded by a physician and blood oxygen saturations were measured using a pulse oximeter. Then, fentanyl 1 μg/kg was administered under direct supervision of a physician. After five minutes, pain score, oxygen saturation, and RR were measured in the above-mentioned order. Results: The data from 67 patients with a average age of 30 years were collected: 77% were male and 23% were female. The average pain score of these patients was 7.3 at the time of admission, which significantly decreased to 3.8 after fentanyl administration (P < 0.001). Upon arrival in emergency department the mean oxygen saturation and RR were 97.1% and 21.5/minute, respectively. After pain control, mean oxygen saturation and RR were 94.9% and 19.2 /minute, respectively, showing a significant decrease only for RR in comparison with that at the time of admission (P < 0.001). Regression analysis of pain score and O2 saturation differentiation showed no significant relation between these variables. There were no side effects or complications of fentanyl observed in these patients. Conclusions: The results of our study revealed no independent causative relationship between pain control and oxygen saturation.