Lower Inspiratory Oxygen Fraction for Preoxygenation

Overview

During the induction period of general anesthesia, surgical patients are inevitably experienced a short period of apnea for endotracheal intubation or other airway manipulation. In order to minimize the risks of hypoxemia during the establishment of artificial airway, pure oxygen (FiO2=100%) is commonly applied to the patients throughout the preoxygenation and induction period. However, high concentration of oxygen therapy has been shown to result in hyperoxemia and substantial oxygen exposure during perioperative period or critical care. There is currently no clinical evidence indicating that preoxygenation with a lower oxygen partial pressure (such as FiO2=60%) during the induction of anesthesia increases the incidence of hypoxemia or other complications. The findings of this proposed clinical study may provide fundamental evidence for the use of different oxygen concentrations in clinical anesthesia during the induction period, and determine the effects of inspired oxygen concentrations on the general postoperative outcomes during general anesthesia.

The administration of 100% oxygen for 3-5 minutes may replace the nitrogen content in the lung cavity (de-nitrogenation) with higher alveolar concentrations of oxygen (greater then 95%). Elevation of oxygen reserve in the lung and oxygen partial pressure in the blood circulation may thus delay the development of hypoxemia (oxygen desaturation; defined as the tissue oxygen saturation below 90%) up to 10 minutes after apnea. On the other hand, there is currently no clinical evidence indicating that preoxygenation with lower oxygen partial pressures (i.e. FiO2= 50-60%) during the induction of anesthesia increases the incidence of hypoxemia or other complications. Most recently, two elegant large-scale clinical trials reported that the supplement of oxygen to patients with acute myocardial infarction or acute ischemic stroke did not provide any clinically beneficial effects in the prognosis of diseases. The results of these two important trials did not support the routine supplement of oxygen in these acute diseases. In addition, high concentrations of oxygen therapy are potentially deleterious, as oxygen toxicity may result in direct tracheobronchial and alveolar damage, absorption atelectasis (lung tissue collapse) and central nervous system toxicity. In cellular levels, hyperoxia increases the production of reactive oxygen species, such as the superoxide anion, the hydroxyl radical, and hydrogen peroxide, which in turn may cause cellular apoptosis and inflammatory response. Therefore, oxygen therapy in clinical settings has been recognized as a two-edged sword and excessive oxygen supplement should be guided closely for its potential toxicity. Currently, there is no clinical evidence that supports the routine administration of 100% oxygen prior to intubation is essential or beneficial. In the contrary, it also remains undetermined if lower fractions of inspiratory oxygen during the induction period of anesthesia may attenuate lung injury or other cellular damage derived from the oxygen toxicity. Therefore, the findings of this proposed clinical study may provide fundamental evidence for the use of different oxygen concentrations in clinical anesthesia during the induction period, and determine the effects of inspiratory oxygen concentrations on the general postoperative outcomes after general anesthesia. This is a randomized, open-label, observer-blind and non-inferiority clinical trial. The research model of study is two-group parallel interventional study. The control group is preoxygenation with 100% oxygen during the induction phase of anesthesia; the experimental group is preoxygenation with 60% oxygen during the induction phase of anesthesia. The anesthetists in-charge are not blinded to the concentrations of oxygen use during induction of anesthesia, but the persons who collected study data will be unaware of the treatment. Block randomization will be generated using a generator software and the assignment of treatment will be sealed in the envelops. This study anticipates in enrolling 1500 participants.