Success or Failure of High-Flow Nasal Oxygen Therapy: The ROX Index Is Good, but a Modified ROX Index May Be Better

The ROX index was calculated for Sp O 2 of 95% and respiratory rates of 20-40 breaths/min using a range of FI O 2 values from 0.4 to 1.0.The gray area indicates ROX values below a cutoff point of 4.88 (1).Respiratory rates in oxygen-dependent patients are expected to be increased.The figure reveals that the ROX index is unlikely to drop below 4.88 with FI O 2 values of up to 0.5, and it would be under the cutoff point with FI O 2 values of 0.8 or higher for the anticipated range of respiratory rates.FI O 2 values of 0.5 and 0.8 are marked with interrupted vertical lines.If Sp O 2 is under or above 95%, all of the presented curves of the calculated ROX will shift slightly downward or upward, respectively.The index is very simple and has the potential to become a routine parameter in clinical practice when supplemental oxygen is used with NHF therapy.The presented figure may help to predict when a patient is expected to fail and could be considered for escalation of care.