Preoxygenation is a standard anesthetic technique which prevents significant hypoxemia during the induction of anesthesia. Complete oxygenation is especially important in clinical situations of difficult intubation or in patients with decreased
FRC, and
in situations where oxygen saturation is critical.
During the induction of anesthesia in children. Airway obstruction and apnea are associated with rapid development of hypoxemia. The decreasing speed of oxyhemoglobin saturation was faster in smaller infants than bigger infants. The most
important
factor determining the speed with which hypoxemia develops in healthy children is probably the oxygen reserve contained in the lungs and its relation to the oxygen consumption of the child.
With decreasing age, the arterial oxygen consumption increases and the ratio of FRC to body weight decreases.
Due to the anatomical structure of an infant's upper airway, it is more difficult to obtaine patient airway in infants than in children. During repeated attempts to intubate the trachea or while waithg for recovery from laryngeal spasms hypoxia
can
occur easily resulting in vislble cyanosis in infants.
This study was carried out to measure the time permissible for apnea before occurance of hypoxia following full oxygenation.
The subjects consisted of 6 randomly selected infants 1-2 month of age, 4.6 ± 0.6 Kg of body weight with no abnormalities of cardiorespiratory functions. After the intramuscular injection of a5ropine, patients were anesthetized through mask
using
oxygen and halothane.
SpO2 and pulse rates were recorded throughout the study. After the patients were intubated, a plug was placed on the distal end of the tube to induce obstructive apnea. As soon as SpO2 decreased to just below 90%, the patients were ventilated
again.
In 2 of the infants. The time required to obtaine 90% saturation was 60 seconds. Within less than 70 seconds, four out of 6 infants had SpO2 below 90% and SpO2 below 80% were noticed in 3 cases. After the reestablishment of ventilation, SpO2
retumed to
the preapneic value within 10 second in all subjects.
There was no evidence of increasing pulse rate as SpO2 levels decreased.
However, pulse rate decreased in all subjects thoughout the study.
In summary, maximum time permissible for apnea in neonate and young infant is approximately one minute. Furthermore, tachycardia should not be used as a sign for the onset of hypoxia.
|