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Maximizing the stability of oxygen delivered via nasal cannula
1Department of Pediatrics, Stanford University School of Medicine, Calif.
Background:
The effective fractional inspired oxygen concentration (FiO2) of supplemental oxygen provided to infants via nasal cannula may be adjusted by changing cannula flow rate or oxygen concentration, factors within our control. However, FiO2 also varies with changes in the patient's breathing, factors beyond our control. While a stable oxygen delivery is desirable, combinations of flow and concentration that maximize stability over time need to be studied.
Objective:
To assess the impact of different weaning strategies on the stability of inspired oxygen concentrations delivered to infants via nasal cannulas and to identify optimum strategies maximizing that stability.
Design:
Theoretical analysis and comparison with previously published measurements.
Methods:
We derived equations predicting the FiO2 delivered to infants via nasal cannula, incorporating traditional adjustments of cannula flow rate and oxygen concentration, as well as considering the impact of the infant's inspiratory time, tidal volume, and fraction of nasal breathing. We compared predicted results with previously published measures and evaluated strategies to maximize oxygen delivery stability over time.
Results:
Predicted values correlated well with published hypopharyngeal measurements (r = .97) and were unbiased, accurate predictors of FiO2. Effective FiO2 was least likely to be affected by changes in patient-controlled controlled factors when the nasal cannula flow rate was as low as possible.
Conclusions:
To minimize variability in oxygen delivery via nasal cannula to infants, cannula flow should be reduced to the lowest possible flow by using undiluted (100%) oxygen. Supplemental oxygen may then be weaned by making small reductions in cannula flow. Cannula oxygen concentration should be reduced below 100% only after the minimum calibrated flow rate is reached. Such a strategy may maximize the stability of delivered oxygen over time as well as minimize the size of changes in delivered oxygen at each step of the weaning process.