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Wednesday, November 5, 2014

Myth Buster: A high FiO2 is protective

So you have a patient come into the emergency room in severe respiratory distress, possibly heart failure, but the SpO2 is normal. In the past it was acceptable to place these patients on a nonrebreather to prevent the patients condition from deteriorating, thus allowing you time to react. This, however, may no longer be acceptable.

I think doctors have gotten much better at not panicking in this regard, as even patients with heart failure, while the used to always get a nonrebreather, that seems to no longer be the case. As with chest pain and any other condition, no oxygen is given unless the SpO2 drops below 94%.

The reasoning for the change was described in an October, 2013, article in Respiratory Care, by Thomas Blakeman.  He said:
According to Downs, the only true indication for prophylactic hyperoxyxgenation is prior to tracheal intubation. Downs furher states that, hypothetically, a patient on FiO2 of 100% and having a PaO2 of 650 m Hg, could drop to 90 mm Hg due to lung function deterioration over a period of 15-20 minutes, but the SpO2 would not drop below 98%. This drop would not be enough to indicate a problem. But over the next 5 minutes the SpO2 wold drop to 92%, alerting the caregiver to investigate. In this scenario the elapsed time until a problem is detected would be 20-25 minutes. If that same patient was on an FiO2 of 30% with a PaO2 of 90 mm Hg and an SpO2 of 99% and experienced the same problem, the SpO2 would decrease to 94% within 10 minutes, alerting caregivers to a problem much earlier. Additionally, if a patient is already receiving FiO2 of 100%, there is no room to increase once a problem is detected."
So, over-oxygenating, a common occurrence in hospitals, may mask an underlying problem, delaying treatment.

  1. Blakeman, Thomas C., "Evidence for Oxygen in the Hospitalized Patient: Is more Really the Enemy of Good," Respiratory Care, October, 2013, volume 58, number 10, pages 1679-1693
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