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Morbid obesity: Hypoxemia physiology

The predominant cause of worsened oxygenation in obesity is a reduction in functional residual capacity (FRC) andincreased airway closure which essentially produces a right-to-left shunt. High FiO2 can contribute to this pathology by promoting atelectasis and further worsening shunting.BMI is correlated to the degree of both atelectasis and shunting. Anesthesia providers should endeavor to prevent this right-to-left shunting byemploying CPAP during induction

Note that 100% FiO2maynot be the best management decision – it promotes atelectasis and if the right-to-left shunt is larger than 30%, willnotimprove PaO2

Obesity and Hypoxemia

  • Cause:right-to-left shuntcaused by airway closure (FRC reduced) and atelectasis
  • Management: CPAP may prevent R-L shunting, consider avoiding 100% O2

Other References

  1. Keys to the Cart: June 5, 2017; A 5-minute video review of ABA Keywords Link