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Friday, October 24, 2014

Myth Buster: FiO2 less than 60% is safe

One of the myths of respiratory therapy is if we get the FiO2 down to 60% we are safe.  In fact, most of us were taught in school that an FiO2 greater than 60% produced more side effects than an FiO2 less than 60%.

This apparently is a myth, and the following is the evidence:
  1. Register et al conducted a study with subjects under going open heart surgery, all of whom were breathing room air preoperatively  It was found that in subjects administered FiO2s of 0.50 postoperatively had a greater degree of hypoxemia on room air on postoperative day 2 than those given sufficient oygen to maintain SpO2 (greater than) 90%.  After repeating the study using only room air intra- and post-operatively, and finding that most subjects did not have a decrease in blood oxygen levels, as compared to preoperative values, it was postulated that the hypoxemia experienced in the first study was due to the use of oxygen during and after surgery.
  1. Garner et al exposed rats with peritonitis to FiO2 of 0.80, 0.4, or 0.21. Mortality was lowest in the FiO2 O.21 group, and highest in the Fio2 0.80 group.  Upon postmortem examination it was found that lung pathology did not differ between the groups but there was substantial liver damage with FiO2 (greater than) 0.21.  It was postulated that free radical formation caused the liver damage. 
This is yet another example that oxygen should not be administered unless necessary, and that every effort should be made to reduce oxygen as soon as possible.  Thankfully, most hospital oxygen protocols call for maintaining an SpO2 of somewhere in the range of 88-94%.  

  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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