History and Objectives: Due to importance of the acid-base balance in the body and conflicting reports on the effect of surgical operation on arterial blood gases, this study was conducted to asses the effect of medium and large scale surgical operations on the arterial blood gases on patients (150) referred to the Shaheed Beheshti hospital of Kashan in 1997.

Materials and Methods: A clinical trial was carried out on 150 patients before and after surgical operation. Patient’s records were collected and those with COPD, anemia and diabetes mellitus were eliminated from the study. Higher arterial blood pH value of 7.4±0.5, PaCo2 40±5 and bicarbonate 24±2 were taken as abnormal findings. Mc Nemar statistical analysis was used to test the results.

Results: 75 males and 75 females participated in the study (Age 49±23). Arterial blood pH showed 21% (P<0.001), PCo2 7.3%, bicarbonate 22%, (P<0.001), metabolic acidosis 14% and respiratory alkalosis 9.3% increase during surgery. No augmentation was observed for metabolic alkalosis.

Conclusion: The present study points to the fact the increased duration of surgical operation has a effect on arterial blood gases and metabolic acidosis is higher.