Chest
Original ResearchCritical Care MedicineIncreases in Endotracheal Tube Resistance Are Unpredictable Relative to Duration of Intubation
Section snippets
Materials and Methods
The West Virginia University Institutional Review Board approved this study and waived the need for consent. The purpose of the study was to evaluate random ETTs from extubated adult patients in the ICU and compare them to new size-matched control tubes for changes in resistance as measured by pressure drop. Pressure drop, a measurement in physics used to quantify the change in pressure across a system, reflects the degree of resistance to flow.17 The pressure drop, as a function of flow rate,
Control Tubes
The measured pressure drop of a tube was directly related to diameter and flow. This association to tube size was consistent with all three flow rates. For each size, there was an increase in pressure drop that was dependent on flow, and the measured pressure drop at each flow level had a very small degree of variability. These results are shown in Figure 2.
Extubated Patient Tubes
Figure 3 demonstrates the differences in the pressure drop of extubated patient tubes compared with size-matched controls at flow rates of
Discussion
ETT size is a critical factor of airway resistance. Clinicians often must make adjustments in the amount of support to help the patient overcome the resistance of the system and the ETT.18, 19, 20 Clinicians assume this resistance is minimized with a properly sized ETT. Pressure drop has been used to describe ETT resistance but only in a pediatric population.21 We sought to quantify the effects of the accumulation of secretions in the adult population and compare them to industry standards. The
Conclusions
ETTs are manufactured in strict accordance to regulation of size. Once placed in the patient, organized secretions accumulate that impact the resistance of the ETT. This change in the tube can be highly variable and occurs for all sizes. The extent of increased resistance in any one patient may be unpredictable. This is clinically important because approximately 50% of the ETTs have a pressure drop of at least 5 cm H2O and can be > 20 cm H2O. In 70 to 80% of cases, the resistance is > 3 SDs
Acknowledgments
Author contributions: Dr. Wilson contributed to data analysis, interpretation, and manuscript preparation. Ms. Gray contributed to sample acquisition and measurements. Dr. Thomas contributed to laboratory oversight and concept development.
Financial/nonfinancial disclosures: The authors have reported to the ACCP that no significant conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.
Other contributions: We thank consultant Paul
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Funding/Support: This project was supported in part by a grant from Covidien Healthcare, previously TYCO Healthcare/Nellcor.
The study was performed at West Virginia University, School of Medicine and West Virginia University Hospitals, Morgantown, WV.
Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (www.chestjournal.org/site/misc/reprints.xhtml).