Even when ventilation appears to be adequate, rebreathing may cause hypercarbia when the dead space of the apparatus is excessive, when very low gas flows(<3.0 L/min) are used in Jackson-Ress or Bain circuits, or as a result of defective carbon dioxide absorption in a circle system.

The purpose of the present study was to determine the effects of head position and intubation method on the arterial blood gas analysis values.

Arterial blood gas analysis (PH, PaCO₂, PaO₂, oxygen saturation and base excess) were performed at 30 minutes after the endotracheal intubation, 5 minutes before the end of surgery and 30 minutes after endotracheal extubation.

The results were obtained as follows ;

1) At 30 minutes after the endotracheal intubation, the PH, PaCO₂, base excess values in group 2 were significantly different from the values in group 1 and 3, the PaCO₂ value was highly significant increased in group 2 but the PaO₂ and oxygen saturation values had no statistical significance in any group.

2) At the 5 minutes before the end of surgery, the PH, PaCO₂, PaO₂ values in group 2 were significantly different from the values in group 1 and 3, but the oxygen saturation and base excess values had no satistical signigicance in any group.

3) At 30 minutes after the endotracheal extubation, the PH, PaCO₂, PaO₂, oxygen saturation, base excess values had no satistical significance in any group