While breathing room air, oxygen saturation drops precipitously to below 90% within about a minute of the start of apnea in the average healthy adult. One of the most important safety measures we use in anesthesia is to preoxygenate our patients prior to induction of anesthesia and in preparation for intubation. This is especially true if we are planning a rapid sequence induction. Adequate preoxygenation can more than double the time to hypoxia during apnea, allowing more time for intubation to occur.
Preoxygenation increases the margin for safety. It treats any pre-existing hypoxemia in the critically ill patient. It also postpones the onset of hypoxia while the patient is apneic during the intubation attempt. This becomes especially important if the intubation attempt becomes difficult and prolonged.
Speed of onset of hypoxia with apnea depends on metabolic rate and on the actual amount of oxygen available in the patient’s functional residual capacity. To see how preoxygenation can effect this let’s review some physiology. Continue reading