2006 OPEN FORUM Abstracts
AIRWAY RESISTANCE IMPOSED BY ENDOTRACHEAL TUBES
William French, MA, RRT
Lakeland
Community
College
,
Kirtland
,
OH
Background
Airway resistance is a critical element in the management of
patients receiving mechanical ventilation. Resistance imposed by artificial
airways is an important part of that element, especially if the patient is
doing any spontaneous breathing. However, as important as this element is,
normal values for resistance through endotracheal
(ET) tubes of different sizes is not published in common sources. Thus, the
point of this study was to provide reference resistance numbers for various
size ET tubes.
Methods and Materials
Measurements were made by attaching an Espirit
ventilator (Respironics) to ET tubes ranging from 5.0
mm to 9.0 mm. The ET tube was attached to a test lung (Michigan Industries) set
at a compliance of 0.05 L/cmH2O. The ventilator was set in volume
control, tidal volume 600 mL, rate 12, square wave
flow pattern. Two consecutive measurements were made and the results calculated
by the ventilator with no variation. Data was reported in cmH2O/L/second.
Results
| ET Tube size | flow rate (L/m) | resistance |
| 5.0 | 40 | 19.5 |
| 5.0 | 60 | 28 |
| 5.0 | 80 | 34 |
| 6.0 | 40 | 8.1 |
| 6.0 | 60 | 12.5 |
| 6.0 | 80 | 15.6 |
| 7.0 | 40 | 4.6 |
| 7.0 | 60 | 6.7 |
| 7.0 | 80 | 8.7 |
| 8.0 | 40 | 3.0 |
| 8.0 | 60 | 4.2 |
| 8.0 | 80 | 5.6 |
| 9.0 | 40 | 2.0 |
| 9.0 | 60 | 2.6 |
| 9.0 | 80 | 3.4 |
Conclusions
Clearly, this was a bench study, and the data should be
viewed accordingly. However, the study does establish reference numbers for
various size ET tubes. It is also interesting to note that the data follow what
could be predicted from the math associated with airway resistance
(R=∆P/flow).