Abstract
We performed a bench (BS) and human (HS) study to test the hypothesis that estimation of tidal volume (VT) during noninvasive helmet pressure support ventilation (nHPSV) would be possible using a turbine driven ventilator (TDV) coupled with an intentional leak single-limb vented circuit. During the BS a mannequin was connected to a lung simulator (LS) and at different conditions of respiratory mechanics, positive end expiratory pressure (PEEP) levels and leaks (30, 50 and 80 L/min). All differences were within the 95% limits of agreement (LoA) in all conditions in the Bland-Altman plot. The overall bias (difference between VT measured by TDV and LS) was 35 ml (95% LoA 10 to 57 ml), 15 ml (95% LoA −40 to 70 ml), 141 ml (95% LoA 109 to 173 ml) in the normal, restrictive and obstructive conditions. The bias at different leaks flow in normal condition was 29 ml (95% LoA 19 to 38 ml). In the HS four healthy volunteers using nHPSV had a pneumotachograph (P) inserted through a mouthpiece to measure subject’s VT.The bias showed a scarce clinical relevance. In conclusions, VT estimation seems to be feasible and accurate in all conditions but the obstructive one. Additional leaks seem not to affect VT reliability.
Highlights
Noninvasive ventilation (NIV) is widely used worldwide to support ventilation and oxygenation in patients with respiratory failure[1]
Intentional leak single-limb vented circuit configuration allows during face mask or nasal ventilation to make an estimation of the delivered VT in all bi-level ventilators as well as in some intensive care unit (ICU) ventilators mainly dedicated for NIV use[14,15,16]
The main findings of the bench study are: (1) No clinically relevant differences were found in VT between turbine driven ventilator (TDV) and lung simulator (LS) in normal and restrictive conditions at all simulated level of positive end expiratory pressure (PEEP); (2) The difference between TDV and LS remained stable across the different tested leak flows; (3) There was a large, clinically relevant, difference in VT in the obstructive condition between TDV and the LS
Summary
Noninvasive ventilation (NIV) is widely used worldwide to support ventilation and oxygenation in patients with respiratory failure[1]. The availability to assess VT during nHPSV might be of importance because it was previously found that high VT during noninvasive ventilation (NIV) in hypoxemic patients may increase lung injury[11,12,13]. Intentional leak single-limb vented circuit configuration allows during face mask or nasal ventilation to make an estimation of the delivered VT in all bi-level ventilators as well as in some intensive care unit (ICU) ventilators mainly dedicated for NIV use[14,15,16]. We hypothesized that a turbine driven ventilator (TDV) coupled with intentional leak single-limb vented circuit and whose leak location is set at the helmet expiratory port would allow to estimate patient’s VT during nHPSV15,16. The aim of the present study was to test this hypothesis on a bench and healthy volunteer study
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