Background: Pulmonary embolism (PE) is a blood clot that blocks and stops blood flow to an artery in the lung. It (PE) is a common and often fatal complication of venous thromboembolic disease (VTE). Pulmonary embolism (PE) is the third leading cause of cardiovascular-related death and is responsible for the hospitalization of a huge number of patients yearly. D-dimer concentration is a diagnostic marker of pulmonary embolism (PE). Aim of the study: This study aimed to assess the impact of anesthesia on D-dimer concentration in patients undergoing surgery associated with high risk for pulmonary embolism. Methods: This prospective observational study was conducted in the Department of Anesthesia & ICU, Mugda Medical College Hospital, Dhaka, Bangladesh during the period from January 2022 to December 2022. In total 57 patients undergoing surgery associated with a high risk for pulmonary embolism were enrolled in this study as study subjects. In this study, we examined the changes imparted by anaesthesia surgery on the end-tidal CO2/O2 compared with the D-dimer. Blood samples were immediately analyzed for fibrinogen and D-dimer concentrations. Breath samples were obtained from 1 min of spontaneous tidal breaths delivered via mouthpiece while the patientst breathed room air. Results: In this study, the mean transoperative value changes of respiratory rate (breaths/min), pulse rate (beats/min), systolic blood pressure (mmHg), SaO2 (%, room air) and minute ventilation (ml/min) were found as 0.23, 11.2, 15.33, 2.05 and 779.42 respectively. The pre-operative mean D-dimer 1042.57 ±202.47 ng/ml had been significantly increased to 1277.58 ±211.28 ng ml postoperatively, where the p-value was found as <0.001. On the other hand, the pre-operative mean End-tidal CO2 ⁄ O2, 0.3 ±0.02 had been decreased to 0.3 ±0.01 (Not significant). But the mean fibrinogen (mg/dl) had increased significantly (p<0.001). Conclusion: As per the findings of this study we can conclude that the stress ...