This study was designed to investigate the ranges of pH, PaO₂ PaCO₂, and SaO₂, before and during halothane-N₂O-O₂-pancuronium anesthesia under controlled ventilation (V_τ: 500-600ml, f: 18-20/min). For the study, 25 surgical patients were selected with physical status ASA class l and ll and age ranging from 20 to 60 years. Samples of arterial and venous blood were collected before and during anesthesia, and sent for immediate gas analysis. The arterial blood gas samples before and during anesthesia revealed values within normal limits. After testing, we were able to control the blood gas patterns by ventilation to produce ideal conditions for patients undergoing anesthesia.