BACKGROUND: SARS-CoV-2 aerosolization during noninvasive positive-pressure ventilation may endanger health-care professionals . Various circuit setups have been described to reduce virus aerosolization . However, these setups may alter ventilator performance . RESEARCH QUESTION: What are the consequences of the various suggested circuit setups on ventilator efficacy during CPAP and noninvasive ventilation (NIV)? STUDY
DESIGN AND METHODS: Eight circuit setups, evaluated in bench tests, consisted of a three-dimensional printed head and an artificial lung . Setups included a dual-limb circuit with an oronasal mask, a dual-limb circuit with a helmet interface, a single-limb circuit with a passive exhalation valve, three single-limb circuits with custom-made additional leaks, and two single-limb circuits with active exhalation valves . All setups were evaluated during NIV and CPAP . The following variables were recorded: the inspiratory flow preceding triggering of the ventilator, the inspiratory effort required to trigger the ventilator, the triggering delay, the maximal inspiratory pressure delivered by the ventilator, the tidal volume generated to the artificial lung, the total work of breathing, and the pressure-time product needed to trigger the ventilator .
RESULTS: With NIV, the type of circuit setup had a significant impact on inspiratory flow preceding triggering of the ventilator (P <.0001), the inspiratory effort required to trigger the ventilator (P <.0001), the triggering delay (P <.0001), the maximal inspiratory pressure (P <.0001), the tidal volume (P = .0008), the work of breathing (P <.0001), and the pressure-time product needed to trigger the ventilator (P <.0001). Similar differences and consequences were seen with CPAP as well as with the addition of bacterial filters . Best performance was achieved with a dual-limb circuit with an oronasal mask . Worst performance was achieved with a dual-limb circuit with a helmet interface . INTERPRETATION: Ventilator performance is significantly impacted by the circuit setup . A dual-limb circuit with oronasal mask should be used preferentially.