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P19 Investigating hypoxic challenge testing methods: patient preference and physiological insights from venturi mask and mouthpiece techniques
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P19 Investigating hypoxic challenge testing methods: patient preference and physiological insights from venturi mask and mouthpiece techniques
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Journal Article
P19 Investigating hypoxic challenge testing methods: patient preference and physiological insights from venturi mask and mouthpiece techniques
2025
Overview
IntroductionHypoxic challenge tests (HCT) are recommended by the British Thoracic Society to assess the requirement for in flight supplemental O2. During an HCT, the FiO2 is reduced to 15% replicating the PiO2 experienced during air travel. Various HCT methods exist, potentially affecting clinical outcomes. In the UK, two main techniques are used, the ‘Venturi mask method’ (V-HCT), which employs 100% N2 via a 40% O2 venturi barrel, and the ‘Mouthpiece method’ (M-HCT), which uses pre-mixed 15% O2 via a mouthpiece. We compared these methods in elderly individuals with airflow obstruction, hypothesising that the M-HCT would induce hyperventilation (assessed via transcutaneous CO2 – tCO2) and potentially yield false-negative results.MethodsParticipants with self-reported COPD or asthma, aged over 60 and naïve to HCT, attended the University of Winchester for a screening visit followed by two experimental visits. Spirometry during the screening visit confirmed airflow obstruction. During the experimental visits, participants completed both V-HCT and M-HCT in a random order, with continuous measurements of tCO2, SpO2, and HR. They also reported any claustrophobia and answered, ‘If asked to perform a HCT by your clinician, what test would you rather perform?’.ResultsTwelve participants completed both HCT methods (see table 1 for demographics). Five found the M-HCT claustrophobic, while none did for the V-HCT, and all preferred the V-HCT. In contrast to our hypothesis, tCO2 levels were similar between methods, with no significant difference from baseline to the final three minutes (M-HCT: 5.1 to 5.0 kPa; V-HCT: 5.1 to 5.1 kPa). Furthermore, ten participants had lower SpO2 nadirs during the M-HCT. Statistical analysis on the grouped data was not feasible as two participants’ SpO2 dropped <83% during the M-HCT, necessitating an FiO2 increase as per ethical guidelines.Abstract P19 Table 1Participant demographicsConclusionPatients preferred the V-HCT, reporting less claustrophobia than the M-HCT, but no evidence of hyperventilation during either method was shown. The reason for lower SpO2 with the V-HCT in ten participants remains unclear, although room air entrainment through the mask’s expiratory ports, raising the FiO2 is a possible explanation. Future studies are required to accurately measure the true FiO2 inhaled during the Venturi technique.
Publisher
BMJ Publishing Group LTD
Subject
