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Carbon dioxide rebreathing in non-invasive ventilation. Analysis of masks, expiratory ports and ventilatory modes. Monaldi Arch Chest Dis

ABSTRACT Carbon dioxide (CO2) rebreathing is a complication of non-invasive ventilation (NIV). Our objectives were to evaluate the ability of masks with exhaust vents (EV) to avoid rebreathing while using positive pressure (PP) NIV with different levels of expiratory pressure (EPAP). Concerning volume-cycled NIV, we aimed to determine whether cylindrical spacers located in the circuit generate rebreathing.
5 healthy volunteers were evaluated. Bi-level PP was used with 3 nasal and 2 facial masks with and without EV. Spacers of increasing volume attached to nasal hermetic masks were evaluated with volume NIV. Inspired CO2 fraction was analyzed.
Rebreathing was zero with all nasal masks and EPAP levels. Using facial masks 1 volunteer showed rebreathing. There was no rebreathing while using all the spacers.
In healthy volunteers, nasal and facial masks with EV prevent rebreathing. In addition, the use of spacers did not generate this undesirable phenomenon.

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    ABSTRACT: Several factors in noninvasive positive pressure ventilation (NIPPV) have proved to be potential causes of failure when this kind of mechanical respiratory assistance is used in patients who suffer from acute (ARF) or chronic (CRF) respiratory failure [1–3]. One such factor is carbon dioxide (CO2) rebreathing [1–4]. This phenomenon consists of rebreathing part of the CO2 expired by the patient during the ventilatory cycle as a result of an accumulation of this gas in the mask or the circuit. Such rebreathing takes place mainly in single-limb circuits (inspiration and expiration into the same tube). Besides the use of such a circuit, there are technical circumstances that play an active role in the presence or elimination of expired CO2: the ventilatory mode [4, 5], type of mask and expiratory port [6–12], as well as the level of positive end-expiratory pressure (PEEP) used [4, 10, 11]. Since 1995, when Ferguson and his collaborators first described such a phenomenon, little research has been done on this issue. The development of technological innovations, mainly in interfaces, has restricted the potential clinical implications of this deleterious phenomenon. Likewise, research works conducted so far have not confirmed whether CO2 rebreathing does have a significant influence on patients’ clinical evolution or is just a potentially, but rarely, harmful phenomenon.
    Noninvasive Mechanical Ventilation, 01/2010: pages 87-92; , ISBN: 978-3-642-11364-2

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