The Science Journal of the American Association for Respiratory Care

2006 OPEN FORUM Abstracts

Variable Resistance Modeling in a High Flow Nasal Cannula (HFNC) Delivery System with Pressure Limitation

Mitchell R Goldstein, MD1,2,3, Martin Sandoval1, Linda L Yang, MD1,2,3, Kristen Hougland, MD1,2,3, Perpetua Lawas-Alejo, MD1,2,3, Bruce D Sindel, MD1,2,3, Mita Shah, MD1,2,3, Gilbert I Furman, MD1,2,3, Clark G Ochikubo, MD1,2,3 and Gilbert I Martin, MD1,2,3. 1Neonatal Medicine, Pomona Valley Hospital Medical Center, Pomona, CA; 2Neonatal Medicine, Citrus Valley Medical Center, West Covina, CA and 3Western University Health Sciences, Pomona, CA.

Background:
The use of HFNC simulating Nasal Continuous Positive Airway Pressure (NCPAP) is widely used in neonatal practice. NCPAP can be altered by varying flow states. This relationship can be affected by patient leak, size of the cannula, and patient minute ventilation. Resistance is an important consideration in the actual propagation of the pressure effect and in excess may precipitate ventilation failure.  We asked if the flows generated under HFNC with pressure limitation could be quantified for idealized flow rates producing minimal resistance.

Methods:
Using a wall flow meter, flows from 1-8 lpm QWall were entrained through a T-connector to a water column at 10 cm H2O and to a distal nasal cannula (AirlifeTM Nasal Oxygen Cannula # 001312) that was submerged to depths from 1-10 cm H2O ∆P = 10-PCannula). Flows QS to the distal cannula were measured and used to calculate Resistance (R) (cmH2O/L/s) according to the relationship R = ∆P/QS.

Results:
As shown in the diagram, HFNC flows delivered with pressure limitation produced variable resistance. A relationship exists between resistance, pressure delivered at the cannula, and wall flow as derived in the equation.

Conclusion:
. HFNC can be optimized by recognizing catheter characteristics that produce the lowest possible resistance values at with ideal flow propagation. Using different catheters with varied resistance profiles may enhance the possibility of success with this modality.



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