PURPOSE: Bronchiolitis & pneumonia account for 93% of all infant lung disease. Continuous positive airways pressure (CPAP) has been used to avert intubation during acute respiratory failure. However, it still fails in up to 35% of cases. Ways of improving CPAP delivery & efficacy need to be investigated. Helium-oxygen gas mixtures (heliox), due to its physical properties, may enhance the physiological benefits of CPAP if used as the driving gas. The aim of this study was to assess if heliox-CPAP can improve tidal volumes and reduce the work of breathing.
METHODS: The ASL5000 Servo Lung simulator was used to compare CPAP effects using 2 driving gas mixtures: 79% helium/21% oxygen (heliox) & 79% nitrogen21% oxygen (air or ’nitrox’). Studies were undertaken at CPAP pressures of 1-10 cmH2O. The tidal volume & imposed work of breathing were noted using the lung simulator for each CPAP setting.
RESULTS: 1) Up to 10 cmH20 CPAP pressure was achievable using heliox. 2) Tidal volumes were up to 20-30% greater with heliox-CPAP compared to nitrox-CPAP. This effect was optimum at CPAP pressures of 4 cmH2O. Heliox-CPAP had no additional benefit beyond pressures of 9 cmH2O. 3) The work of breathing (WOB) was reduced by up to 70-80% when using heliox. This effect was also optimum at pressures of 4 cmH2O.
CONCLUSION: Heliox can be effectively used to deliver up to 10 cmH2O CPAP.The optimum CPAP pressure for improvements in tidal volume and work of breathing is 4 cmH2O.There is no additional benefit in tidal volume beyond 9 cmH2O of heliox-CPAP.
CLINICAL IMPLICATIONS: Heliox-CPAP may increase the efficacy of CPAP and reduce the number of infants requiring invasive respiratory support.Recommendations for using heliox-CPAP in clinical practice: 1) Start at 4 cmH2O. 2) Do not exceed 9 cmH2O. 3) When weaning, coming directly off non-invasive support at 4 cmH2O is a bigger step for heliox-CPAP than for conventional nitrox-CPAP. It is therefore recommended that patients are weaned further - in steps down to 1-2 cmH2O before stopping heliox-CPAP altogether.
DISCLOSURE: Mina Chowdhury, Grant monies (from industry related sources) BOC Medical; Shareholder None; Employee None; Fiduciary position (of any organization, association, society, etc, other than ACCP None; Consultant fee, speaker bureau, advisory committee, etc. None; Other None.