Optimisation of tidal volumes given with self-inflatable bags without additional oxygen☆,☆☆
Introduction
The European Resuscitation Council has recommended smaller tidal volumes during basic life support ventilation in order to minimise gastric inflation [1]. Studies in both bench models and clinical studies confirmed that smaller tidal volumes resulted in decreased peak airway pressure, which, in turn, makes gastric inflation less likely [2], [3], [4], [5], [6]. The approach to administering small tidal volumes in these studies was to use a paediatric instead of an adult self-inflatable bag. In clinical studies, we have shown that small tidal volumes were sufficient to maintain adequate ventilation and oxygenation, but only if an FiO2 of approximately 0.5 was used [7]. This is remarkable, since exhaled tidal volumes when using a self-inflatable bag are usually only about 50% of the maximum bag volume, resulting in tidal volumes of approximately 350 ml with a paediatric self-inflatable bag (maximum volume, 700 ml). We have demonstrated this in several previous studies [2], [3], and have suggested that although the European Resuscitation Council recommendation states a tidal volume of 500 ml, only 350 ml may be delivered with a paediatric bag This is especially important when additional oxygen is not available at the scene. Using a paediatric self-inflatable bag with room-air resulted in adequate ventilation, but deteriorating oxygenation [8]. As such, ensuring a smaller risk of gastric inflation may be offset by severe oxygenation problems, rendering the strategy of attempting to deliver tidal volumes of 500 ml with a paediatric self-inflatable bag questionable.
One approach to overcome this problem may simply be to increase tidal volumes given with a paediatric self-inflatable bag, but not to a level produced by an adult self-inflatable bag that is associated with gastric inflation [9]. It seemed logical to evaluate the performance of a self-inflatable bag with a size between the maximum volume of a paediatric (700 ml) and an adult (1500 ml) bag. The purpose of the present study was to determine whether a bag with a maximum volume of 1100 ml may be able to combine both advantages; minimising the risk of gastric inflation, while ensuring adequate carbon dioxide elimination and oxygenation, even with room-air. Our hypothesis was that there would be no differences in respiratory variables and blood gases when employing either self-inflatable bag.
Section snippets
Materials and methods
The experimental protocol of this study was reviewed and approved by the Institutional Review Board of the study institution. We kept the Institutional Review Board informed of the process of the study at all times. It was agreed that the value of the study using pre-oxygenation would have been at best questionable. The consensus was that it would be ethical to perform the study in healthy ASA I and ASA II patients who signed written informed consent before being enrolled into the
Results
Fifty patients were enrolled into the study, and randomised to receive bag-valve-mask ventilation with either a newly developed medium-size (n=25) or an adult (n=25) self-inflatable bag. There were no significant differences in age, weight, or height between groups (Table 1). When compared with an adult self-inflatable bag, the medium-size bag resulted in significantly lower exhaled tidal volume (P<0.001; Table 2), oxygen saturation, and partial pressure of oxygen (P<0.05; Table 3). When using
Discussion
In this experiment, we have demonstrated that bag-valve-mask ventilation with a medium-size self-inflatable bag (maximum volume, 1100 ml) maintains adequate ventilation and oxygenation, although the oxygenation was slightly better when using an adult self-inflatable bag (maximum volume, 1500 ml).
When smaller tidal volumes of 500 ml (about 6 ml · kg−1) were recommended by the European Resuscitation Council [1], it was not described how to deliver this volume. Interestingly, in a clinical study
Acknowledgements
Supported, in part, by the Department of Anaesthesiology, University of Lübeck, Germany. We are indebted to Susanne Flaig RN, and Rolf Müller RN, for technical assistance and support throughout the study.
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Reply
2014, Journal of Clinical Anesthesia
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Presented, in part, as an abstract at the 13th Annual Meeting of the American College of Emergency Physicians, Las Vegas, NV, October 1999.
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The authors do not have a conflict of interest with regards to the devices used in this experiment.