MAXIMIZING THE STABILITY OF OXYGEN DELIVERED VIA NASAL CANNULA

Background: The effective fractional inspired oxygen-concentration (Fi O2) of supplemental oxygen provided to infants via nasal cannula may b e adjusted by changing cannula flow rate or oxygen concentration, fact ors 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 ma ximize stability over time need to be studied. Objective: To assess th e impact of different weaning strategies on the stability of inspired oxygen concentrations delivered to infants via nasal cannulas and to i dentify optimum strategies maximizing that stability. Design: Theoreti cal analysis and comparison with previously published measurements. Me thods: We derived equations predicting the FiO2 delivered to infants v ia nasal cannula, incorporating traditional adjustments of cannula flo w rate and oxygen concentration, as well as considering the impact of the infant's inspiratory time, tidal volume, and fraction of nasal bre athing. We compared predicted results with previously published measur es and evaluated strategies to maximize oxygen delivery stability over time. Results: Predicted values correlated well with published hypoph aryngeal measurements (r=.97) and were unbiased, accurate predictors o f FiO2. Effective FiO2 was least likely to be affected by changes in p atient controlled factors when the nasal cannula flow rate was as low as possible. Conclusions: To minimize variability in oxygen delivery v ia nasal cannula to infants, cannula flow should be reduced to the low est possible flow by using undiluted (100%) oxygen. Supplemental oxyge n may then be weaned by making small reductions in cannula flow. Cannu la oxygen concentration should be reduced below 100% only after the mi nimum calibrated flow rate is reached. Such a strategy may maximize th e stability of delivered oxygen over time as well as minimize the size of changes in delivered oxygen at each step of the weaning process.