During induction of anesthesia, apnea may persist in the case of difficult intubation or fiberoptic guide intubation. In that situation hypoxemia and hypercarbia may occur even though preoxygenation and hyperventilation has performed before apnea
star.
Sometimes anesthesiologist perform preoxygenation with mixed oxygen and nitrous oxide gas to facilitate and smooth induction.
The aim of this study was to know the apnenic time that arterial oxygen saturation drop below 93% in the patients who was preoxygenated with 100% oxygen or mixed gas (oxygen: nitrous oxide 1:1 ratio) before apnea begin and to know whether nasal
oxygen
insufflation during apnea affect arterial oxygen tension.
Study was conducted in three groups. Each group has 13 patients. After induction of anesthesia with thiopental, pancuronium and isoflurane 1 vol%, Group 1 (Air group) and Group 2 (O2 group) were ventilated with facemask with 100% oxygen for 5
minutes
and then remained apneic state in air (Group 1) or nasal insufflation of oxygen (1 L/10 kg/min) (Group 2) with patent airway. Group 3 (N2O group) was ventilated with O2 and N2O in 1:1 ratio for 5 minutes and remained apneic state in air Apnea
continued
until either SaO2 were recorded. During apnea period PaO2, PaCO2, Sao2, MAP HR were measured 1 min interval.
Duration of apnea and mean minimum saturation for Group 1, 2 and 3 were 7(1, 8, 30.(0.9 min and 96.6(2.4%, 99.1(1.5%, 95.7(2.5% (mean(SD) respectively. In Group 2, SaO2 never fell below 95% during the entire 8 min apnea in any subject.
PaCO2 were increased by 5.8 mmHg (Group 1), 7.4 mmHg (Group 2) 7.8 mmHg (Group 3) at first 1 min and then linealy increased by 2.9 mmHg/min for Group 1 and 2 and by 3.2 mmHg/min in Group 3 during apnea period. There was no difference in MAP among
three
groups during apneic period but HR of Group 3 showed significant increase after 2 min compared to Group 2.
In conclusion, preoxygenation followed by insufflation of oxygen via nasal oxygen cannula provides at least 8 min of adequate oxygenation in healthy apneic patients whose airways are unobstructed in whom the trachea is not intubated. It is safe
method
not to use preoxygenation with mixed gas of N2O before apnea if there is any possibilty of difficult intubation or difficulty in establishing patent airway.
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