Does the Use of a Pop-Off Valve Affect the Accuracy of Delivered Flow and Pressure in Heated High-Flow Nasal Cannula Therapy in Pediatric Patients?

Abstract

Background:

The practice of managing work of breathing and oxygenation through the use of heated high-flow nasal cannula (HHFNC) therapy has continued to increase at our institution. Based on our bench study published in 2012, our HHFNC set-up does not include the use of an in-line pop-off valve (POV). With our organization's recent transition to using the Optiflow Junior 2 nasal cannulas and the RT330 heated single-limb circuit, we performed an additional bench study to assess whether use of the POV in conjunction with the Optiflow Junior 2 cannulas and RT330 circuit may prevent the system from reaching the manufacture-listed maximum flows.

Methods:

A bench study was conducted comparing maximal flows and pressures in a HHFNC system with and without a POV in line. Flows for cannula sizes were set as follows: extra-small (ES) 8 L/min, small (S) 9 L/min, medium (M) 10 L/min, large (L) 23 L/min and extra-large (EL) 25 L/min. For this study, three cannulas of each size, along with three POV were used. For each set of three cannulas (for each size), three sets of data were collected for a total of 45 data sets. Data were collected at 37°C. FIO₂ was 1.0. Measurements of flow and pressure were acquired using a Magnehelic pressure manometer and a TSI/Alnor 41403 Flow Meter. Between measurements of each set of three cannulas, the baseline flow was recalibrated using the TSI/Alnor 41403 flow meter.

Results:

The most significant pressure differences with the POV inline occurred in the L and EL cannulas (Table 1). The pressure within the circuit averaged 28.40 cm H₂O when using the POV with the EL cannula and 27.9 with the L cannula, although the POV limit is stated as 40 cm H₂O. There was a correlated difference observed in the measured flow with the POV inline for the L and EL cannulas. Respective flows of 20.3 and 21.6 L/min were observed, as compared with manufacturer listed maximum flows of 23 and 25 L/min respectively (Table 2). Though measured values for the M, S and ES cannulas (POV inline) resulted in P values of <0.05, the differences would not reach clinical significance for the patient.

Conclusions:

Our current practice for not utilizing the POV inline was validated in this study. The circuit pressures were not extreme. With the POV inline, the circuit pressures and cannula flows were reduced significantly below the manufacture listed maximum flow level in the L and EL cannulas, which could potentially impact the patient's course of treatment.