Abstract
Purpose: Variable ventilation is superior to control mode ventilation in a number of circumstances. The nature of the breathing file used to deliver the variable rate and tidal volume has not been formally examined.
Methods: We compared two different noise files in a randomized prospective trial of variable ventilation. Pigs were anesthetized, intubated, and mechanically ventilated. Oleic acid was infused to introduce lung injury. The animals were ventilated at a tidal volume of 7 mL·kg−1, in variable mode, with either physiologically-derived noise (variability file − 1,587 breath intervals-obtained from a spontaneously breathing volunteer;n=10) or a variability file of identical length derived from computergenerated white noise (n=10).
Results: The physiologically-derived noise had a power law α-exponent of −0.27 and a Hölder exponent of −0.38, indicative of auto-correlated noise. The computer-generated noise had an α-exponent of −0.52 and a Hölder exponent of −0.49, indicative of white noise. Both files showed multifractal characteristics. There were no differences between groups, at any time period, for PaO2, PaCO2, and static or dynamic respiratory system compliance. No differences were observed between groups for wet:dry lung weight ratios or for interleukin-8 in bronchoalveolar lavage fluid.
Conclusion: This study demonstrates that the nature of the variability files, chosen to drive the variable ventilator, had no effect on indices of gas exchange or respiratory mechanics in this model. A considerable overlap of the multifractal files existed. The potential to drive a variable ventilator using algorithmderived files with multifractal characteristics, thereby eliminating the requirement to use physiologically-derived signals, is discussed.
Résumé
Objectif: La ventilation en mode variable est supérieure à la ventilation en mode contrôlée dans plusieurs situations. La nature du fichier de respiration utilisé pour engendrer la fréquence et le volume courant variable n’a pas été évaluée de façon formelle.
Méthode: Nous avons comparé deux fichiers de bruit différents dans une étude prospective randomisée de la ventilation en mode variable. Les cochons ont été anesthésiés, intubés et ventilés mécaniquement. Ils ont reçu une perfusion d’acide oléique afin de provoquer une lésion pulmonaire. Les animaux ont été ventilés à un volume courant de 7 mL·kg−1, en mode variable, avec soit du bruit de provenance physiologique (fichier de variabilité — 1587 intervalles de respiration — obtenus d’un volontaire respirant spontanément ; n=10) ou un fichier de variabilité de longueur identique dérivé d’un bruit blanc généré par ordinateur (n=10).
Résultats: Le bruit d’origine physiologique avait un exposant α de la loi de puissance de −0,27 et un exposant de Hölder de −0,38, ce qui indique un bruit auto-corrélé. Le bruit généré par ordinateur avait un exposant α de −0,52 et un exposant de Hölder de −0,49, ce qui indique un bruit blanc. Les deux fichiers ont montré des caractéristiques multifractales. Il n’y a pas eu de différence entre les groupes, à n’importe quelle période de temps, pour la PaO2, la PaCO2, et la conformité statique et dynamique du système respiratoire. Aucune différence n’a été observée entre les groupes en ce qui touche aux rapports de poids oedème pulmonaire/poumon sec ou pour l’interleukine 8 dans le liquide de lavage bronchoalvéolaire.
Conclusion: Cette étude démontre que la nature des fichiers de variabilité sélectionnés pour entraîner le respirateur en mode variable n’a pas eu d’effet sur les indices d’échange gazeux ou de mécanique respiratoire dans ce modèle. Un chevauchement considérable est apparu dans les fichiers multifractals. La possibilité d’entraîner un respirateur en mode variable avec des fichiers dérivés d’algorithmes avec des caractéristiques multifractales, éliminant ainsi le besoin de recourir à des signaux d’origine physiologique, est discutée ici.
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Conflict of interest: Dr. Mutch and the University of Manitoba stand to gain financially if the ventilator discussed in this paper is marketed. No other author has a similar financial arrangement.
Support: James S. McDonnell Foundation.
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Froehlich, K.F., Graham, M.R., Buchman, T.G. et al. Physiological noise versus white noise to drive a variable ventilator in a porcine model of lung injury. Can J Anesth 55, 577–586 (2008). https://doi.org/10.1007/BF03021431
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DOI: https://doi.org/10.1007/BF03021431