Tidal Volume Estimation during Helmet Noninvasive Ventilation: an Experimental Feasibility Study.

Area of Science:

• Respiratory Medicine
• Biomedical Engineering
• Critical Care

Background:

• Noninvasive helmet pressure support ventilation (nHPSV) is an emerging ventilatory support method.
• Accurate estimation of tidal volume (V_T) is crucial for effective ventilation management.
• Current methods for V_T estimation in nHPSV with intentional leaks are limited.

Purpose of the Study:

• To evaluate the feasibility and accuracy of tidal volume (V_T) estimation during nHPSV using a turbine-driven ventilator (TDV) with a single-limb vented circuit.
• To assess the impact of varying respiratory mechanics, positive end-expiratory pressure (PEEP), and leak conditions on V_T estimation accuracy.

Main Methods:

• Bench study (BS) using a lung simulator (LS) with controlled respiratory mechanics and PEEP levels.
• Human study (HS) involving four healthy volunteers breathing via nHPSV with a pneumotachograph for V_T measurement.
• Analysis of bias and 95% limits of agreement (LoA) using Bland-Altman plots.

Main Results:

• In the BS, V_T estimation showed good agreement with the LS across normal, restrictive, and obstructive conditions, with overall biases of 35ml, 15ml, and 141ml, respectively.
• In normal conditions, varying leak flows (30-80 L/min) did not significantly impact V_T bias (29ml).
• In the HS, the bias between TDV and pneumotachograph measurements was of scarce clinical relevance.

Conclusions:

• Tidal volume estimation during nHPSV using a TDV and vented circuit is feasible and accurate in normal and restrictive respiratory conditions.
• The accuracy of V_T estimation is compromised in obstructive conditions.
• Intentional leaks in the circuit do not appear to significantly affect the reliability of V_T estimation.