The Science Journal of the American Association for Respiratory Care

2012 OPEN FORUM Abstracts


Gary R. Lowe1, Randy Willis1, Shirley Holt3, Tracy Thurman3, Mark Heulitt1,2; 1Respiratory Care Services, Arkansas Children’s Hospital, Little Rock, AR; 2Department of Pediatrics, Critical Care Medicine, University of Arkansas for Medical Sciences, Little Rock, AR; 3Arkansas Children’s Hospital Research Institute, Little Rock, AR

Background: High pressures can be generated within the circuit of heated high flow nasal cannula (HHFNC) systems. A comparative study was undertaken to determine the pressures generated within the circuit and the patient interface of two manufacturers HHFNC devices. Objective: Evaluate the pressures generated within the circuit and at the patient interface. Methods: A bench study was conducted comparing maximal flows and pressures in a HHFNC system with two manufacturers’ nasal cannula devices [Fisher/Paykel (F/P) and Neotech Ram (RA)]. Flow rates for cannula sizes were set as follows: 6 LPM in F/P premature infant cannulas (F/P1) and RA preemie infant cannulas (RA1), 7 LPM in F/P infant cannulas (F/P2) and RA newborn cannulas (RA2), and 8 LPM in F/P pediatric cannula (F/P3) and RA infant cannulas (RA3). Five cannulas were used for each test. Data were collected at 32° and 37°C. FiO2 was 1.0. The external diameters and lengths of all cannulas were measured with calipers. Measurements of flow and pressure were acquired using the Biopac MP-100 System. For all cannulas, one 0-35 LPM pneumotachograph (PNT) was placed where the large bore tubing connects to the nasal cannula and one 0-35 LPM PNT was connected directly to the portion of the cannula that would be inserted in the nares. Pressure was calibrated with an SJ-16 vertical manometer. All output signals were routed via an analog channel box into the Biopac MP-100 data acquisition unit converting them into digital signals that can be processed with a computer. Signals were obtained at a rate of 1000 samples per second. Results: The circuit pressures noted in F/P cannulas were significantly higher (60% – 70%, p < 0.001) than in the RA cannulas. However, there was < 10% difference in pressures generated at the patient interface between manufacturers. Measured pressure at the patient interface was less than 0.50 cmH2O for both manufacturers (F/P 0.29-0.42; RA 0.27-0.42 cmH20). Temperature settings did not appear to have an effect on pressures generated in either case. The diameters of the F/P cannulas were smaller than the equivalent size of RA cannulas. Conclusion: Based on these results, F/P cannulas showed significantly higher circuit pressures than RA cannulas. Additionally, the diameters of the F/P cannulas may be responsible for the degree of back pressures generated in the circuit. Minimal pressures were generated at the patient interface in both manufacturers’ cannulas. Sponsored Research - None