The variation of FiO₂ with circuit type and peak inspiratory flow rate during non-invasive respiratory support using domiciliary ventilators and its significance during the COVID-19 pandemic

Abstract

Background The COVID-19 pandemic has resulted in increased admissions with respiratory failure and there have been reports of oxygen failure and shortages of machines to deliver ventilation and Continuous Positive Airway Pressure (CPAP). Domiciliary ventilators which entrain room air have been widely used during the pandemic. Poor outcomes reported with non-invasive respiratory support using ventilators which lack an oxygen blender could be related to an unreliable Fraction of inspired O2 (FiO2). Additionally, with concerns about oxygen failure, the variety of ventilator circuits used as well as differing peak inspiratory flow rates (PIFR) could impact on the FiO2 delivered during therapy with domiciliary ventilators. Methods In a series of bench tests, we tested the effect of choice of circuit and different PIFR on the FiO2 achieved during simulation of ventilation and CPAP therapy using domiciliary ventilators. Results FiO2 was highly dependent upon the type of circuit used with circuits with an active exhalation valve achieving similar FiO2 at lower oxygen flow rates than circuits using an exhalation port. During CPAP therapy, high PIFR resulted in significantly lower FiO2 than low PIFR. Conclusions This study has implications for oxygen usage as well as delivery of non-invasive respiratory support during therapy with domiciliary ventilators when these are used during the second wave of COVID-19.

Long-term home mechanical ventilation using a noninvasive ventilator via tracheotomy in patients with myasthenia gravis: a case report and literature review

“…The active exhalation valve circuit provides higher FiO 2 at lower oxygen flow rates than the passive exhalation valve circuit. 41 However, the patient in our case was not primarily hypoxic, and the patient’s dyspnea was relieved by the use of a single-limb circuit with a passive exhalation port providing some pressure support. It has been shown that during home IMV, the use of passive exhalation circuit is no less important than the use of active exhalation circuit in ensuring good respiratory gas exchange and maintaining safety.…”

“…Currently, the circuits used in noninvasive ventilators include single-limb circuit with a passive exhalation port (some manufacturers call it ‘the leak valve’), active exhalation port in a dual-limb circuit, active exhalation port in a coaxial circuit, active exhalation port in single-limb circuit. 41 For single-limb circuit, the inspiratory pathways share the same limb with the expiratory pathways, so there is a risk of re-inhaling CO 2 . To avoid this, the ventilator delivers fresh air continuously at high enough speeds during expiration to flush the dead spaces of the circuit.…”

Mask interfaces and devices for home noninvasive ventilation in children

“…16,21 The double-limb circuit exists as a "classical" double tubing or a co-axial tubing which is mainly used for anesthesia or in ICU, but is available for home NIV. [60][61][62] A careful check of the integrity of the co-axial circuit must be always done to prevent potential malfunctioning. [61][62][63] The single-limb circuit, which is the most used for home NIV, can be used with a calibrated leak either at the mask level (vented mask) or directly in the circuit for a use with non-vented masks.…”

“…There are 3 types of circuits: the single‐limb circuit, the single‐limb circuit with an active exhalation valve, and the double‐limb circuit 16,21 . The double‐limb circuit exists as a “classical” double tubing or a co‐axial tubing which is mainly used for anesthesia or in ICU, but is available for home NIV 60–62 . A careful check of the integrity of the co‐axial circuit must be always done to prevent potential malfunctioning 61–63 …”

Anaesthesiology as an oasis amid the crisis of the vital medicine ‘Oxygen’- innovations and local modifications

“…They inferred a 50% reduction of oxygen during supported and controlled ventilation with an active exhalation valve breathing circuit, thereby explaining its connotation during the resource limitation era of the COVID-19 pandemic. [ 24 ]…”