Continuous positive airway pressure for respiratory support during COVID-19 pandemic: a frugal approach from bench to bedside

Annals of Intensive Care

Table 1 Bench study

Changes expressed in % of baseline value without filter		Low inspiratory effort (Pmus = −5 cm H₂O)			Moderate inspiratory effort (Pmus = − 10 cm H₂O)
Changes expressed in % of baseline value without filter		∆ Volume	∆ WOB imposed	∆ WOB patient	∆ Volume	∆ WOB imposed	∆ WOB patient
Resistance 5 cm H₂O/L/s	FF-CPAP 6 cm H₂O	− 16.5%	+ 105.8%	+ 34.2%	− 15.5%	+ 98.3%	+ 29.9%
Resistance 5 cm H₂O/L/s	FF-CPAP 10 cm H₂O	− 15.3%	+ 64.8%	+ 32.5%	− 15.9%	+ 69.0%	+ 27.7%
Resistance 15 cm H₂O/L/s	FF-CPAP 6 cm H₂O	− 10.9%	+ 90.4%	+ 13.2%	− 11.3%	+ 95.9%	+ 8.5%
Resistance 15 cm H₂O/L/s	FF-CPAP 10 cm H₂O	− 9.4%	+ 51.7%	+ 14.5%	− 9.6%	+ 57.6%	+ 9.8%

Influence of the filter on tidal volume and work of breathing during low and moderate simulated inspiratory efforts
Pmus simulated muscle pressure, ∆ Volume tidal volume variation induced by the filter as compared to baseline (without filter), ∆ WOBimposed variation of work of breathing imposed by the CPAP induced by the filter as compared to baseline (without filter). WOBimposed was calculated from the airway pressure–volume loop. ∆ WOBpatient variation of simulated patient’s work of breathing needed to maintain the tidal volume constant after having added the filter. WOBpatient was calculated from the muscle pressure–volume loop, PEEP positive end-expiratory pressure, FF-CPAP filter frugal continuous positive airway pressure (see text for definition)