Helmet continuous positive airway pressure for patients' transport using a single oxygen cylinder: A bench study.

Abstract

Background: Continuous positive airway pressure (CPAP) is frequently used to treat patients with acute respiratory failure in out-of-hospital settings. Compared to a facemask, the helmet has many advantages for the patient but requires a minimum gas flow of 60 L/min to avoid CO₂ rebreathing. The aim of the present bench study was to evaluate the performance of four Venturi devices, connected to a single oxygen cylinder, in delivering helmet-CPAP with clinically relevant gas flow, fraction of inspired oxygen (FiO₂)_, and positive end-expiratory pressure (PEEP) values.

Methods: Three double-inlet Venturi systems (EasyVent, Ventuplus, Compact-HAR) were connected to full 5-L oxygen cylinders using a double flowmeter, and their oxygen requirements to reach different setups (flow 60-80 L/min; FiO₂ 0.4-0.5-0.6, PEEP 7.5-10-12.5 cmH₂O) were tested. The fourth Venturi system (O2-MAX) was directly attached to the tank, and the flow and FiO₂ delivered at preset FiO₂ 0.3 and 0.6 were recorded. The runtime of the cylinder was assessed.

Results: EasyVent, Ventuplus, and O2-MAX were able to deliver helmet-CPAP with clinically useful setups when connected to a single oxygen cylinder, while Compact-HAR did not. The runtime of the cylinders ranged between 28 and 60 minutes according to the preset flow and FiO₂. The delivered gas flow decreased slowly and linearly with the drop in cylinder pressure until its exhaustion.

Conclusions: Helmet-CPAP might be provided using portable Venturi systems connected to an oxygen cylinder, but not all of them are able to deliver it. The use of a double flowmeter allows delivery of both high flow and high FiO₂ when double-inlet Venturi systems are used. Due to the flow drop observed during the cylinder consumption, a flow >60 L/min should be set when helmet-CPAP is started. Considering the flow drop phenomenon, the estimated duration of the tank runtime can be used with a margin of safety when planning patient transport.