The Science Journal of the American Association for Respiratory Care

2011 OPEN FORUM Abstracts

HIGH FLOW NASAL CANNULA: WHEN DOES HIGH FLOW MASK HYPOVENTILATION?

Rita T. Giordano2, Lisa Tyler2, Daniela H. Davis1, Richard J. Lin1,2; 1Anesthesiology and Critical Care Medicine, The Children's Hospital of Philadelphia, Philadelphia, PA; 2Respiratory Care, The Children's Hospital of Philadelphia, Philadelphia, PA

Background: High flow nasal cannula (HFNC) has become popular as a mode of support which can be better tolerated than a mask interface but may still offer benefits of non-invasive support such as overcoming inspiratory resistance and providing end expiratory pressure. The application of HFNC is appealing for small children and infants where achieving an adequate mask fit that is well tolerated may be challenging. It is important to understand the effective FiO2 provided by different flow rates of nasal cannula oxygen so that safe parameters can be established for use of HFNC which minimize the risk of masking hypoventilation. However, there is a lack of data available in the literature. Methods: We developed an empiric equation between FiO2 and nasal cannula flow rate which would 1)account for the commonly used rule of thumb for nasal cannulas in adults (0.04 increase for each lpm), 2)be asymptotic to an FiO2 of 1.0 with increasing flow, and 3)have a scale factor for minute ventilation, since the effective FiO2 is less than the FiO2 of the nasal cannula gas due to entrainment of air to meet minute ventilation demands. Results: The expression FiO2=0.21+0.79(1-exp(f*ln(0.49)/MV)) has the specified features, where f is the nasal cannula flow rate, and MV is the minute ventilation. The predicted values for MV of 3 lpm are comparable to those measured in infants by Kuluz (Resp Care 46(9), 897-901 (2001)). This expression is graphed below for MV of 3, 6, and 12 lpm. For comparison, measured FiO2 for an LTV 1200 with minute ventilations of 3 and 6 lpm is also shown. Conclusions: We have been able to develop an expression which provides estimates of FiO2 as a function of nasal cannula flow that are consistent with a commonly used empiric rule for adults and with available neonatal data. This can be the basis of guidelines for use of HFNC which minimizes risk of masking hypoventilation. Sponsored Research - None