الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Induction of general anesthesia causes an increase in intrapulmonary shunt, which is mainly caused by atelectasis formation. Atelectasis appears within minutes of induction of anesthesia in the lungs of 85–90% of healthy, non-obese patients .
In cases of difficult airway management, duration of non-hypoxic apnea, defined as apnea with SpO2 > 90%, depends on the reserves of oxygen held within the body, which are mainly in the functional residual capacity (FRC). To a lesser degree, intrapulmonary shunt will also influence the duration of non-hypoxic apnea. Therefore, avoiding atelectasis formation may increase the duration of non-hypoxic apnea and, in consequence, increase the margin of safety .
It has been shown that FIO2 used during pre-oxygenation greatly influences atelectasis formation. Even a FIO2 of 0.8 will prevent atelectasis formation compared to 100% oxygen, although, at the cost of a decrease in the non-hypoxic apnea duration .
Atelectasis formation can be effectively prevented by the application of positive end-expiratory pressure (PEEP) applied during the induction of anesthesia, despite the use of 100% of oxygen. Therefore, applying PEEP during the entire induction of anesthesia with 100% O2 may increase the duration of the non-hypoxic apnea .
Functional anatomy of the lungs
The lung parenchyma can be subdivided into three airway categories based on functional lung anatomy (Table I). The conductive airways provide basic gas transport, but no gas exchange takes place in them. The next group of airways, which have smaller diameters, are transitional airways. They are conduits for gas movement, and additionally perform limited gas diffusion and exchange. Finally, the smallest respiratory airways’ primary function is gas exchange. Ventilation–perfusion (V/Q) relationships are defined by the function of the respiratory airways .
Table ( I ) : Functional airway divisions 5