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; 2Dept. of Pediatrics, Critical Care Medicine, University of Arkansas for Medical Sciences, Little Rock, AR; 3Arkansas Children’s Hospital Research Institute, Little Rock, AR

Background: Heated high flow nasal cannulas (HHFNC) have become an integral part of pediatric respiratory care. The set-up used at our institution does not include a pop-off valve (POV). The impact that POVs could have on flows and pressures during HHFNC has not been widely investigated. Objective: Evaluate the effect of an in line POV on flow and pressure. Methods: A bench study was conducted comparing maximal flows and pressures in a HHFNC system with and without a POV in line. Flow rates for cannula sizes were set as follows: 6 LPM in premature infant cannulas (PMIC), 7 LPM in infant cannulas (IC), 8 LPM in pediatric cannulas (PC), and 60 LPM in small adult cannulas (SAC). Five cannulas and POVs were used for each test. Data were collected at 32° and 37°C. FiO2 was 1.0. Measurements of flow and pressure were acquired using the Biopac MP-100 System. For the PMIC, IC, and PC, 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. The SAC was configured the same way, but two 0-160 LPM PNTs were used. Pressure was calibrated with 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 pressure differences with the POV in line were significantly lower with both temperature settings in the PMIC. The mean flow differences with the POV in line were significantly lower with both temperature settings in the PMIC and IC. This was also noted in the PC at the higher temperature setting. The pressure within the circuit averaged 29.98 cmH2O when using the POV, although the POV limit is stated as 40 cmH2O. The pressure generated at the patient interface was < 0.41 cmH2O in all cases with the exception of the SAC which generated a maximum pressure of 2.06 cmH2O at the patient interface. Conclusion: The current practice for not utilizing the POV in-line was validated in this study. The circuit pressures were not extreme, and would not be translated to the patient based on these results. With the POV in line, the flows were reduced which could impact the patient’s course of treatment. Sponsored Research - None