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Horsley, Alex R. and O'Neill, Katherine and Downey, Damian G. and Elborn, J. Stuart and Bell, Nicholas J. and Smith, Jaclyn and Owers-Bradley, John (2016) Closed circuit rebreathing to achieve inert gas wash-in for multiple breath wash-out. ERJ Open Research, 2 (1). 00042-2015. ISSN 2312-0541

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Abstract

Multiple breath wash-out (MBW) testing requires prior wash-in of inert tracer gas. Wash-in efficiency can be enhanced by a rebreathing tracer in a closed circuit. Previous attempts to deploy this did not account for the impact of CO2 accumulation on patients and were unsuccessful. We hypothesised that an effective rebreathe wash-in could be delivered and it would not alter wash-out parameters.

Computer modelling was used to assess the impact of the rebreathe method on wash-in efficiency. Clinical testing of open and closed circuit wash-in–wash-out was performed in healthy controls and adult patients with cystic fibrosis (CF) using a circuit with an effective CO2 scrubber and a refined wash-in protocol.

Wash-in efficiency was enhanced by rebreathing. There was no difference in mean lung clearance index between the two wash-in methods for controls (6.5 versus 6.4; p=0.2, n=12) or patients with CF (10.9 versus 10.8; p=0.2, n=19). Test time was reduced by rebreathe wash-in (156 versus230 s for CF patients, p<0.001) and both methods were well tolerated. End wash-in CO2 was maintained below 2% in most cases.

Rebreathe–wash-in is a promising development that, when correctly deployed, reduces wash-in time and facilitates portable MBW testing. For mild CF, wash-out outcomes are equivalent to an open circuit.

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