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. 2004 Dec;8(6):R398-402.
doi: 10.1186/cc2954. Epub 2004 Oct 6.

Effect of lung compliance and endotracheal tube leakage on measurement of tidal volume

Sami I Al-Majed  1 , John E Thompson, Kenneth F Watson, Adrienne G Randolph
Affiliations

Effect of lung compliance and endotracheal tube leakage on measurement of tidal volume

Sami I Al-Majed et al. Crit Care. 2004 Dec.

Abstract

Introduction: The objective of this laboratory study was to measure the effect of decreased lung compliance and endotracheal tube (ETT) leakage on measured exhaled tidal volume at the airway and at the ventilator, in a research study with a test lung.

Methods: The subjects were infant, adult and pediatric test lungs. In the test lung model, lung compliances were set to normal and to levels seen in acute respiratory distress syndrome. Set tidal volume was 6 ml/kg across a range of simulated weights and ETT sizes. Data were recorded from both the ventilator light-emitting diode display and the CO2SMO Plus monitor display by a single observer. Effective tidal volume was calculated from a standard equation.

Results: In all test lung models, exhaled tidal volume measured at the airway decreased markedly with decreasing lung compliance, but measurement at the ventilator showed minimal change. In the absence of a simulated ETT leak, calculation of the effective tidal volume led to measurements very similar to exhaled tidal volume measured at the ETT. With a simulated ETT tube leak, the effective tidal volume markedly overestimated tidal volume measured at the airway.

Conclusion: Previous investigators have emphasized the need to measure tidal volume at the ETT for all children. When ETT leakage is minimal, it seems from our simulated lung models that calculation of effective tidal volume would give similar readings to tidal volume measured at the airway, even in small patients. Future studies of tidal volume measurement accuracy in mechanically ventilated children should control for the degree of ETT leakage.

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Figures

Figure 1
Figure 1
Schematic diagram demonstrating the placement of CO2SMO and NMV pnueumotachometers in infant and pediatric models.
Figure 2
Figure 2
Effect of decreasing lung compliance on the difference between effective tidal volume and tidal volume at the endotracheal tube (ETT) in the infant, pediatric, and adult test lungs with no leak around the ETT.
Figure 3
Figure 3
Effect of decreasing lung compliance on the difference between effective tidal volume and tidal volume at the endotracheal tube (ETT) in the infant and pediatric test lung models with 20% and 30% simulated ETT leakage.
See this image and copyright information in PMC

References

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