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Reply to

preoxygenation by spontaneous breathing or noninvasive positive pressure ventilation with and without positive end-expiratory pressure

Hanouz, Jean-Luc

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European Journal of Anaesthesiology: February 2016 - Volume 33 - Issue 2 - p 145
doi: 10.1097/EJA.0000000000000381
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Editor,

We thank Drs Glossop and Esquinas for their interest in our study1 and the opportunity to discuss the results. They highlight that the patients included in our study were not representative of emergency surgical or critically ill patients in whom rapid airway control and hence rapid and efficient preoxygenation was required.2 We fully agree. However, the endpoints of our study (primary endpoint: time from face mask positioning to expired oxygen fraction >90%; secondary endpoint: time to peripheral O2 saturation = 93%) did not enable us to include emergency surgical and critically ill patients. Especially, the time until peripheral O2 saturation decreased to 93% was not considered ethical in emergency care and critically ill patients. We definitely believe that the time to desaturate must be studied. At the present time, our results may support the design of specific studies aimed at comparing different preoxygenation methods in emergency anaesthesia and critical care. We agree that such studies must be the next step.

They also questioned the use of noninvasive positive pressure ventilation without positive end-expiratory pressure. At the present time, most anaesthesia ventilators include a noninvasive positive pressure ventilation mode. One hypothesis of the study was that positive inspiratory pressure per se could result in faster preoxygenation compared with spontaneous breathing, at least from direct and indirect mechanisms. First, positive pressure ventilation requires perfect positioning of the face mask which could focus practitioner care on face mask position. Second, positive inspiratory support could prevent inward air leaks avoiding dilution of inspired oxygen, thus increasing the efficacy of preoxygenation. Third, positive pressure ventilation increases end-expiratory lung volume through the recruitment of collapsed alveoli and increases tidal volume resulting in a more efficient washing out of nitrogen. And fourth, positive pressure ventilation requires monitoring of airway pressure, tidal volume and inspiratory and expiratory gases. Thus, we wished to study a group with positive pressure ventilation without positive end-expiratory pressure. The results of our study support this hypothesis since the time to achieve preoxygenation was comparable between groups with positive pressure ventilation and with positive end-expiratory pressure. We fully agree with Drs Glossop and Esquinas that adding positive pressure ventilation to continuous positive airway pressure during preoxygenation could be valuable but we think that it should be comparable to the positive pressure ventilation and positive end-expiratory pressure group included in our study.

We think that our study supports the use of positive pressure ventilation with or without positive end-expiratory pressure during preoxygenation of patients whatever their condition. Beyond decreasing the time to achieve preoxygenation, the most important benefit could be an increased efficiency and reproducibility of preoxygenation which has been shown to remain a major issue.3 A single study will never answer all questions but could in fact raise some more questions. We thank Drs Glossop and Esquinas for highlighting some limits of our study1 and opening the way to further studies on preoxygenation.

Acknowledgements relating to this article

Assistance with the letter: none.

Financial support and sponsorship: this work was supported by CHU de Caen, Caen, France.

Conflicts of interest: none.

References

1. Glossop AJ, Esquinas AM. Preoxygenation by spontaneous breathing or noninvasive positive pressure ventilation with and without positive end-expiratory pressure: a future direction for high-risk intubations? Eur J Anaesthesiol 2016; 33:143–144.
2. Hanouz JL, Lammens S, Tasle M, et al. Preoxygenation by spontaneous breathing or noninvasive positive pressure ventilation with and without positive end-expiratory pressure: a randomised controlled trial. Eur J Anaesthesiol 2015; 32:881–887.
3. Baillard C, Depret F, Levy V, et al. Incidence and prediction of inadequate preoxygenation before induction of anaesthesia. Ann Fr Anesth Reanim 2014; 33:e55–e58.
© 2016 European Society of Anaesthesiology