Published online December 31, 2007
PEDIATRICS Vol. 121 No. 1 January 2008, pp. 82-88 (doi:10.1542/peds.2007-0957)
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ARTICLE

Heated, Humidified High-Flow Nasal Cannula Therapy: Yet Another Way to Deliver Continuous Positive Airway Pressure?

Zuzanna J. Kubicka, MDa, Joseph Limauro, RRTb and Robert A. Darnall, MDa,c

a Departments of Pediatrics
b Respiratory Therapy
c Physiology, Dartmouth Medical School and Dartmouth-Hitchcock Medical Center, Lebanon, New Hampshire

OBJECTIVE. The goal was to estimate the level of delivered continuous positive airway pressure by measuring oral cavity pressure with the mouth closed in infants of various weights and ages treated with heated, humidified high-flow nasal cannula at flow rates of 1–5 L/minute. We hypothesized that clinically relevant levels of continuous positive airway pressure would not be achieved if a nasal leak is maintained.

METHODS. After performing bench measurements and demonstrating that oral cavity pressure closely approximated levels of traditionally applied nasal continuous positive airway pressure, we successfully measured oral cavity pressure during heated, humidified, high-flow nasal cannula treatment in 27 infants. Small (outer diameter: 0.2 cm) cannulae were used for all infants, and flow rates were left as ordered by providers.

RESULTS. Bench measurements showed that, for any given leak size, there was a nearly linear relationship between flow rate and pressure. The highest pressure achieved was 4.5 cmH2O (flow rate: 8 L/minute; leak: 3 mm). In our study infants (postmenstrual age: 29.1–44.7 weeks; weight: 835–3735 g; flow rate: 1–5 L/minute), no pressure was generated with the mouth open at any flow rate. With the mouth closed, the oral cavity pressure was related to both flow rate and weight. For infants of ≤1500 g, there was a linear relationship between flow rate and oral cavity pressure.

CONCLUSIONS. Oral cavity pressure can estimate the level of continuous positive airway pressure. Continuous positive airway pressure generated with heated, humidified, high-flow nasal cannula treatment depends on the flow rate and weight. Only in the smallest infants with the highest flow rates, with the mouth fully closed, can clinically significant but unpredictable levels of continuous positive airway pressure be achieved. We conclude that heated, humidified high-flow nasal cannula should not be used as a replacement for delivering continuous positive airway pressure.

Key Words: oxygen delivery • high-flow nasal cannula • continuous positive airway pressure • infant

Abbreviations: HHHFNC—heated, humidified, high-flow, nasal cannula • CPAP—continuous positive airway pressure • OD—outer diameter • NCPAP—nasal continuous positive airway pressure

Accepted Jul 27, 2007.