To the Editor.—In their commentary “Oxygen Therapy for Bronchiolitis,”1 Bass and Gozal pointed out the significant risks of chronic or intermittent hypoxia on cognition in children as documented in their excellent systematic review.2In their commentary, they took the position that what is known about the effects of chronic and intermittent hypoxia can be extrapolated to an acute illness, bronchiolitis. As they pointed out, there have been no articles addressing the effects of mildly decreased oxygen saturation in this condition. The 2 entities for which there is high-quality evidence for cognitive effects of hypoxia, congenital heart disease (CHD) and sleep-disordered breathing (SDB), are very different from bronchiolitis. With CHD there is chronically low pulse oxygen saturation (Spo2) until surgical correction is achieved. With SDB a child undergoes nightly periods of oxygen deprivation until diagnosis is made and intervention takes place. In articles referenced in the cited review,2 this diagnosis usually occurred at 3 to 5 years of age. Especially in SDB, it may be the sleep disturbance itself that affects behavior and cognition. On the other hand, bronchiolitis is a self-limited disease, with respiratory symptoms usually resolving within 3 to 7 days.The actual oxygen content of blood is determined by the type, amount, and physiologic characteristics of hemoglobin as well as Spo2 and Po2. It is the amount of oxygen in the blood and the ability of the hemoglobin to carry and deliver oxygen to tissues that determine the adequacy of brain and tissue oxygenation. In a previously healthy infant older than 2 months with acute bronchiolitis and without other physiologic risk factors such as acidosis, there is little difference in oxygen content delivered to tissues at 90% than at the traditionally used value of 92%. The Collaborative Home Infant Monitoring Evaluation Study Group showed transient decreases in Spo2 to <90% in healthy infants, including some children >2 months of age, during normal sleep.3Schroeder et al4 showed that 16 of 62 patients had hospitalization prolonged by a mean of 1.6 days because of a perceived need for supplemental oxygen to maintain Spo2 at ≥93% despite other signs of clinical improvement. The authors concluded that continuous monitoring of Spo2 leads to prolonged hospitalization because of administration of oxygen in response to brief transient decreases in Spo2. In the previously healthy child, recovery from acute bronchiolitis is relatively predictable. Once the infant's respiratory rate is decreasing, work of breathing is returning to normal, wheezing has decreased, and Spo2 is stable on the shoulder of the oxyhemoglobin dissociation curve, continuous monitoring of Spo2 can be discontinued and discharge planning can be accomplished.Although the systematic review raised concerns about the impact of chronic hypoxia on cognitive and developmental outcome, until there are more substantial data linking short-term, intermittent hypoxia with behavioral and/or cognitive outcome, the recommendations contained in their guideline represent the “best evidence” available.