Chest
Volume 136, Issue 4, October 2009, Pages 1006-1013
Journal home page for Chest

Original Research
Critical Care Medicine
Increases in Endotracheal Tube Resistance Are Unpredictable Relative to Duration of Intubation

https://doi.org/10.1378/chest.08-1938Get rights and content

Background

Accumulated secretions after intubation can affect the resistance of an endotracheal tube (ETT). Our objective was to measure extubated patient tubes and size-matched controls to evaluate differences in resistance.

Methods

New ETTs, with internal diameters of 7.0 through 8.5 mm, were tested as controls to establish the resistance of each size group as measured by pressure drop. Measurements were obtained using a mass flowmeter and pressure transducer. Pressure drop was measured at three flow rates. Seventy-one patient ETTs were evaluated after extubation by an identical method and compared with controls.

Results

In each control group, pressure drop was tightly clustered with low variation and no overlap between sizes. A total of 73 to 79% of the patient ETTs had a pressure drop of > 3 SDs of size-matched controls at all flow rates. Pressure drop in 48 to 56% (across three flow rates) of extubated tubes was equivalent to the next smaller size of controls. At 60 and 90 L/min, 10% and 15% of patient tubes, respectively, had the pressure drop of a control tube three sizes smaller. The pressure drop was unpredictable relative to the duration of intubation.

Conclusions

Organized secretions can significantly increase resistance as measured by the pressure drop of ETTs. The degree of change was highly variable, occurs in all sizes, and was unrelated to the duration of intubation. The performance of an ETT may be comparable to new tubes one to four sizes smaller. This may impact the tolerance of ventilator weaning.

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

References (0)

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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).

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