Oxygen flow rate was set at 8 L/min, and patients continued to breathe normally at tidal volumes for 3 min. The face mask was applied to the patients in the supine position in both groups. Preoxygenation was done with an appropriately sized clear face mask connected to 100% oxygen filled anesthesia machine. By pushing the button of oxygen instead of medical air, preoxygenation was accomplished. Before preoxygenation, the tidal volume was checked over 6 ml/kg and end tidal CO 2 concentration was checked by using 8 L/min flow of medical air under the circle system. Afterwards the face mask was applied firmly to patient's face in order to prevent air leakages, but not so tightly as to cause discomfort. įor baseline measurements, patients breathed room air with the tidal volume breathing technique for 3 min to record O 2, CO 2 concentration and oxygen saturation in the supine position. The change in the relationship between functional residual capacity and closing capacity causes an increased ventilation perfusion mismatch, which leads to a lower oxygen stores than in young adults. In elderly people total lung capacity is relatively unchanged by the age, but functional residual capacity falls below closing capacity which increases with age. However, patients with a decreased capacity of oxygen loading or an increased oxygen extraction, or both, are desaturated during apnea much faster than healthy patients. Hence, if most of the nitrogen in the lung is replaced by oxygen, end tidal expiratory oxygen concentration is reached over 90% as the result of adequate preoxgenation. Maximal preoxygenation is achieved when the alveolar, arterial, tissue, and venous compartment are all filled with oxygen. Preoxygenating with 100% oxygen before induction of general anesthesia and delaying the onset of arterial hemoglobin desaturation during subsequent apnea is standard practice in many institutions.

Normal tidal volume per kg anesthesia