Elsevier

Resuscitation

Volume 36, Issue 1, January 1998, Pages 23-27
Resuscitation

Effectiveness of mask ventilation in a training mannikin. A comparison between the Oxylator EM100 and the bag-valve device

https://doi.org/10.1016/S0300-9572(97)00091-9Get rights and content

Abstract

The demands for an optimal ventilation apparatus are that it can be easily handled, achieves a sufficiently high ventilation volume, and minimizes gastric inflation. Our aim was therefore to carry out a study in a training mannikin to find out whether the Oxylator EM100, compared with the bag, obtains improved ventilation and a decrease in gastric inflation. In a randomized crossover study, 72 subjects were selected (24 physicians, 44 nurses and 4 auxiliary nurses), chosen from the operating theatre, emergency department and intensive care unit of two hospitals. We used the Ambu®-Bag Mark III with mask No. 4, the Oxylator EM100 with a pressure setting of 35 cm H2O run in the manual setting, the Ambu®-Man C mannikin as well as the Ambu®-CPR computer program. The resuscitation cycles of the standard two-rescuer's adult procedure lasted 3 min each, with a 3-min pause between the crossover procedure. The participants could improve their ventilatory volume with the Oxylator EM100 by 635 ml (95% confidence interval 578–692 ml) compared with the bag ventilation. The number of subjects who could attain a mean ventilatory volume of 800 ml or more increased from 15% to 98.6% (P<0.001). Compared with the bag, the increase of adequate respirations (≥800 ml) obtained by the Oxylator EM100 for the individual participants amounted to a median of 91% (P<0.001). Moreover, conventional ventilation caused in 42% one or several instances of gastric inflation, whereas no such reactions occurred with the Oxylator EM100. The Oxylator EM100 showed significantly better results in the mannikin than the bag. Of most importance is a significant lowering of gastric inflation and less so a marked increase in ventilatory volume. Our trial procedure with a relatively high lung compliance and a high oesophageal sphincter opening simulated favorable conditions. Owing to a large in vivo variability of these magnitudes, a direct testing in real patients with circulatory arrest is indicated.

Introduction

In 70–80% of cases, ventricular fibrillation is the most frequent cause of sudden cardiac death [1]. It can only be reversed in the few minutes after circulatory arrest. Hypoxemia, hypercapnia and acidosis then lower the fibrillation threshold and increase defibrillation tolerance [2]. Basic measures for resuscitation are therefore aimed at emergency oxygenation and carbon dioxide elimination. They depend, in part, on the ventilatory volume. Respiration, however, can cause problems. As long as the patient is not intubated, the medical personnel generally use a face mask and bag. This ventilatory technique, however, is difficult to manage and frequently causes complications [3]. Large and/or rapidly administered volumes lead to high pressure peaks with gastric inflation and risk of regurgitation and aspiration. Moreover, the magnitude of respiratory volume is still unclear [2]. This uncertainty is reflected in different recommendations 1, 4. The American Heart Association (AHA) recommends an optimal ventilatory dose of 800–1200 ml of air [1]. This recommendation is difficult to achieve for many emergency medical technicians [5], nursing personnel [6], anaesthetists [7], and even physicians [8]with reasonable instructions and practical experience. The European Resuscitation Council (ERC) is of the opinion that 500–600 ml of ventilatory volume suffices [4]. According to the ERC, this guideline is easier to follow and definitely eliminates the risk of gastric inflation. Moreover, if air is supplemented with oxygen, sufficient oxygenation can be obtained. It is, however, questionable whether enough carbon dioxide can be exhaled. In any case, even in the presence of a minimal circulation, the occurrence of hypercapnia depends directly on ventilatory magnitude [9].

An optimal ventilation apparatus should therefore be one that can be easily handled and still attain a sufficiently high ventilatory volume without risking gastric inflation.

The Oxylator EM100 is supposed to fulfil these requirements. Since pertinent investigations have not yet been undertaken, however, our aim was to study in a training mannikin whether the Oxylator EM100 compared with the Ambu®-Bag in fact improves ventilation and reduces gastric inflation.

Section snippets

Participants, materials and methods

This is a randomized crossover study. The AHA recommends 10–12 respirations per minute [1]. In our experience, on the average a maximum of 5–6 proper respirations (≥800 ml) per minute is attained. We therefore assumed that the Oxylator EM100 would attain an improvement from 6 to 9 proper respirations per minute or 27 per 3 min, respectively. Taking into account an α-error of 0.05 and a power of 0.8, at least three subjects are needed to prove this effect [10].

Group comparison

The participants obtained with the Oxylator EM100 a mean ventilatory volume of 1.196 ml (95% confidence interval of 1161–1231 ml) compared with 556 ml (95% confidence interval 507–605 ml) for the bag-valve-mask ventilation. The number of subjects who obtained an average ventilatory volume of 800 ml or more increased from 15% (11/72) with the Ambu®-Bag to 98.6% (70/72) with the Oxylator EM100 (P<0.001). Altogether, 46% (33/72) in the mask-bag group and 49% (35/72) in the Oxylator EM100 group

Discussion

In contrast to bag-valve-mask ventilatory volume, with the use of the Oxylator EM100, nearly all our participants obtained the ventilatory volume as recommended by the AHA. Handling of the Oxylator EM100 was simple and directions for use minimal. Moreover, no abdominal insufflations were encountered. It is particularly noteworthy that for the Ambu®-Bag, even with the low tidal volumes of 400–600 ml, which according to Baskett et al. are perceived adequate for resuscitation [12], the mean values

Conclusion

In summary we came to the following conclusions:

  • 1.

    With the Oxylator EM100, ventilation of a training mannikin is effective, with minimal risk of gastric inflation, simply and quickly learned.

  • 2.

    In a mannikin with a lung compliance of 50–55 ml/cm H2O and an oesophageal opening pressure of 30 cm H2O, the Oxylator EM100 obtains markedly less abdominal insufflation and a higher respiratory volume than the Ambu®-Bag.

  • 3.

    The trial procedure simulated a favorable situation with a high threshold for abdominal

Acknowledgements

We wish to express our gratitude to Mr R. Schoch, A Bollinger AG, Ch-Fehraltorf representative in Switzerland of CPR Medical Devices, Inc., Canada, who made the Oxylator EM100 available to us and assisted us in its management. We also wish to thank all the participants for their cooperation in carrying out this study and the reviewers for their valuable suggestions.

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