Performance of different continuous positive airway pressure helmets equipped with safety valves during failure of fresh gas supply

Purpose: We assessed the performance of different continuous positive airway pressure (CPAP) helmets equipped with a safety valve during discontinuation of fresh gas flow. Methods: This was a physiological study of five healthy volunteers. We delivered CPAP (fresh gas flow 60 l/min, FiO2 60%, PEEP 5 cmH2O) with three different helmets in a random sequence: 4Vent (Rüsch), HelmHAR-cp (Harol) and CaStar CP210 (StarMed). For each helmet we randomly applied, for up to 4 min, three disconnections of fresh gas flow: helmet inlet (Dinlet), flowmeter (Dflowmeter) and gas source (Dsource). We continuously recorded from a nostril: end-tidal CO2 (Pet- CO2), inspiratory CO2 (PiCO2), fraction of inspired oxygen (FiO2) and respiratory rate (RR). Results: During every disconnection we observed an increase in PiCO2 and PetCO2 with a drop in FiO2, while RR did not change. Fio2 decreased more quickly in the CaStar, equipped with the largest safety valve, during Dsource and Dflowmeter, while FiO2 decreased more quickly during Dinlet in CaStar and in 4Vent. Pico2 resulted in a lower increase in CaStar during Dsource and Dflowmeter compared to 4Vent. Petco2 in CaStar increases more slowly compared to 4Vent during Dsource and more slowly compared to the other two helmets during Dflowmeter. During Dinlet similar degrees of CO2 rebreathing and Pet- CO2 were recorded among all the helmets. Conclusions: To minimize CO2 rebreathing during disconnection of the fresh gas supply while performing helmet CPAP, it is desirable to utilize large helmets with a large anti-suffocation valve. Monitoring and alarm systems should be employed for safe application of helmet CPAP.