Determinants of the cuff-leak test: a physiological study

Prinianakis George, Alexopoulou Christina, Mamidakis Eutichis, Kondili Eumorfia, Georgopoulos, Georgopoulos Dimitris

Description

The cuff-leak test has been proposed as a simple method to predict the occurrence of post-extubation stridor. The test is performed by cuff deflation and measuring the expired tidal volume a few breaths later ( V T ). The leak is calculated as the difference between V T with and without a deflated cuff. However, because the cuff remains deflated throughout the respiratory cycle a volume of gas may also leak during inspiration and therefore this method (conventional) measures the total leak consisting of an inspiratory and expiratory component. The aims of this physiological study were, first, to examine the effects of various variables on total leak and, second, to compare the total leak with that obtained when the inspiratory component was eliminated, leaving only the expiratory leak. Methods In 15 critically ill patients mechanically ventilated on volume control mode, the cuff-leak volume was measured randomly either by the conventional method (Leak conv ) or by deflating the cuff at the end of inspiration and measuring the V T of the following expiration (Leak pause ). To investigate the effects of respiratory system mechanics and inspiratory flow, cuff-leak volume was studied by using a lung model, varying the cross-sectional area around the endotracheal tube and model mechanics. Results In patients Leak conv was significantly higher than Leak pause , averaging 188 ± 159 ml (mean ± SD) and 61 ± 75 ml, respectively. In the model study Leak conv increased significantly with decreasing inspiratory flow and model compliance. Leak pause and Leak conv increased slightly with increasing model resistance, the difference being significant only for Leak pause . The difference between Leak conv and Leak pause increased significantly with decreasing inspiratory flow ( V ' I ) and model compliance and increasing cross-sectional area around the tube. Conclusion We conclude that the cross-sectional area around the endotracheal tube is not the only determinant of the cuff-leak test. System compliance and inspiratory flow significantly affect the test, mainly through an effect on the inspiratory component of the total leak. The expiratory component is slightly influenced by respiratory system resistance.

Sujets

• Compliance
• Mechanical ventilation
• Résistance

Informations

• Publié par: biomed
• Publié le: 01 janvier 2004
• Nombre de lectures: 17
• Langue: English

Extrait

Available onlinehttp://ccforum.com/content/9/1/R24

February 2005 Vol 9 No 1 Open Access Research Determinants of the cuffleak test: a physiological study 1,2 1 1 1 George Prinianakis , Christina Alexopoulou , Eutichis Mamidakis , Eumorfia Kondili and 1 Dimitris Georgopoulos

1 Intensive Care Medicine Department, University of Crete, University Hospital of Heraklion, Heraklion, Crete, Greece 2 Director, Intensive Care Medicine Department, University of Crete, University Hospital of Heraklion, Heraklion, Crete, Greece

Corresponding author: Dimitris Georgopoulos, [e-mail]

Received: 3 August 2004 Revisions requested: 2 September 2004 Revisions received: 26 October 2004

Accepted: 3 November 2004

Published: 29 November 2004

Critical Care2005,9:R24R31 (DOI 10.1186/cc3012) This article is online at: http://ccforum.com/content/9/1/R24

© 2004 Prinianakiset al.; licensee BioMed Central Ltd.

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/ licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract IntroductionThe cuffleak test has been proposed as a simple method to predict the occurrence of postextubation stridor. The test is performed by cuff deflation and measuring the expired tidal volume a few breaths later (V). The leak is calculated as the difference betweenVwith and without a deflated T T cuff. However, because the cuff remains deflated throughout the respiratory cycle a volume of gas may also leak during inspiration and therefore this method (conventional) measures the total leak consisting of an inspiratory and expiratory component. The aims of this physiological study were, first, to examine the effects of various variables on total leak and, second, to compare the total leak with that obtained when the inspiratory component was eliminated, leaving only the expiratory leak. Methods15 critically ill patients mechanically ventilated on volume control mode, the cuffleak In volume was measured randomly either by the conventional method (Leak ) or by deflating the cuff at conv the end of inspiration and measuring theV). To investigate theof the following expiration (Leak T pause effects of respiratory system mechanics and inspiratory flow, cuffleak volume was studied by using a lung model, varying the crosssectional area around the endotracheal tube and model mechanics. Results, averaging 188 ± 159 ml (mean ±In patients Leak was significantly higher than Leak conv pause SD) and 61 ± 75 ml, respectively. In the model study Leak increased significantly with decreasing conv inspiratory flow and model compliance. Leak and Leak increased slightly with increasing model pause conv resistance, the difference being significant only for Leak . The difference between Leak and pause conv Leak increased significantly with decreasing inspiratory flow (Vand model compliance and' ) pause I increasing crosssectional area around the tube. ConclusionWe conclude that the crosssectional area around the endotracheal tube is not the only determinant of the cuffleak test. System compliance and inspiratory flow significantly affect the test, mainly through an effect on the inspiratory component of the total leak. The expiratory component is slightly influenced by respiratory system resistance.

Keywords:compliance, inspiratory flow, mechanical ventilation, postextubation stridor, resistance

C= model airway compliance;CO);= endinspiratory static compliance of the respiratory system (ml/cmH ∆Leak = difference between Leak rs 2 conv and Leak ;∆P= difference between peak inspiratoryPbetween methods;∆R= difference betweenRandR; Leak = cuffleak vol pause aw,peak aw rs int conv ume obtained by the conventional method; Leak = cuffleak volume obtained when the cuff was deflated at the end of the endinspiratory pause; pause P= airway pressure; PEEP = positive endexpiratory pressure;R= model airway resistance;R= minimum resistance of the respiratory system; aw int R= maximum resistance of the respiratory system;V' = flow at the airway opening;V' = inspiratory flow;V= expired tidal volume;V= expir rs I T T,baseline atoryVmeasured by averaging five consecutive breaths;V= expiratoryVmeasured when cuff was deflated;V= expiratory tidal volume T T,defl T T,pause measured at the end of the endinspiratory pause.

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