However, accumulation of carbon dioxide (described above) would remain the limiting factor. Apneic oxygenation is more than a physiologic curiosity. It can be employed to provide a sufficient amount of oxygen in thoracic surgery when apnea cannot be avoided, and during manipulations of the airways such as bronchoscopy, intubation, and surgery of the upper airways. However, because of the limitations described above, apneic oxygenation is inferior to extracorporal circulation using a heart-lung machine and is therefore used only in emergencies, short procedures, or where extracorporal circulation cant be accessed. Use of PEEP valves is also an accepted alternative (5 cm H2O in average weight patients and 10 cm H2O significantly improved lung and chest wall compliance in morbidly obese patients).In 1959, Frumin described the use of apneic oxygenation during anesthesia and surgery. Of the eight test subjects in this landmark study, the highest recorded PaCO2 was 250 millimeters of mercury, and the lowest arterial pH was 6.72 after 53 minutes of apnea. Apnea scientific studies
Studies found spleen volume is slightly reduced during short breath-hold apnea in healthy adults. Apnea test in determining brain death
A recommended practice for the clinical diagnosis of brain death formulated by the American Academy of Neurology hinges on the conjunction of three diagnostic criteria: a coma, absence of brainstem reflexes, and apnea (defined as the inability of the patient to breathe unaided: that is, with no life support systems like ventilators). The apnea test follows a delineated protocol.
With the onset of apnea, low pressure develops in the airspace of the lungs because more oxygen is absorbed than CO2 is released. With the airways closed or obstructed, this will lead to a gradual collapse of the lungs and suffocation. However, if the airways are open, any gas supplied to the upper airways will follow the pressure gradient and flow into the lungs to replace the oxygen consumed. If pure oxygen is supplied, this process will serve to replenish the oxygen stored in the lungs and resume sufficient ventilation. The uptake of oxygen into the blood will then remain at the usual level, and the normal functioning of the organs will not be affected. A detriment to this hyperoxygenation is the occurrence of nitrogen washout, which can lead to absorption atelectasis.However, no CO2 is removed during apnea. The partial pressure of CO2 in the airspace of the lungs will quickly equilibrate with that of the blood. As the blood is loaded with CO2 from the metabolism without a way to remove it, more and more CO2 will accumulate and eventually displace oxygen and other gases from the airspace. CO2 will also accumulate in the tissues of the body, resulting in respiratory acidosis. Under ideal conditions (i.e., if pure oxygen is breathed before onset of apnea to remove all nitrogen from the lungs, and pure supplemental oxygen is insufflated), apneic oxygenation could theoretically be sufficient to provide enough oxygen for survival of more than one hours duration in a healthy adult.