High FiO2 and atelactasis

Q: One of the tricks to avoid atelectasis is to employ high FiO2?

A) True

B) False

Answer: B

The high fraction of inspired oxygen (FiO2) in the air actually expedites atelectasis.

Normal (ambient) air contains 79% of inert nitrogen. As human lungs are exposed to ambient air since birth, it is in equilibrium with the nitrogen that's dissolved in pulmonary arteriolar and capillary blood. In normal circumstances, at the distal end of the bronchial tree, the pressure gradient forcing nitrogen into mixed venous blood is extremely low, and so nitrogen absorbs slowly. In other words, it acts like an alveolar splint or scaffolding and thus prevents or delays atelectasis. In contrast, intraalveolar oxygen quickly reabsorbed along a steep pressure gradient into deoxygenated mixed venous blood.

High FiO2 in the air disperses nitrogen. As described above, distal atelectasis develops quickly.

#pulmonary

#ventilators

References:

1. Park M, Jung K, Sim WS, Kim DK, Chung IS, Choi JW, Lee EJ, Lee NY, Kim JA. Perioperative high inspired oxygen fraction induces atelectasis in patients undergoing abdominal surgery: A randomized controlled trial. J Clin Anesth. 2021 Sep;72:110285. doi: 10.1016/j.jclinane.2021.110285. Epub 2021 Apr 7. PMID: 33838534.

2. Benoît Z, Wicky S, Fischer JF, Frascarolo P, Chapuis C, Spahn DR, Magnusson L. The effect of increased FIO(2) before tracheal extubation on postoperative atelectasis. Anesth Analg. 2002 Dec;95(6):1777-81, table of contents. doi: 10.1097/00000539-200212000-00058. PMID: 12456458.