A Comparison of Gas Flow Resistance in Parker Flex-tip and Mallinckrodt RAE Nasal
Endotracheal Tubes
THESIS
Presented in Partial Fulfillment of the Requirements for the Degree Master of Science in
the Graduate School of The Ohio State University
By
Joshua L. Perry, D.D.S.
Graduate Program in Dentistry
The Ohio State University
2013
Dr. Simon Prior – Advisor
Dr. William Johnston
Dr. William Brantley
Copyright by
Joshua L. Perry
2013
Abstract
Introduction:
The newer Parker Flex-Tip endotracheal tube causes less trauma and/or bleeding
than more traditional designs during naso-tracheal intubation. However, the Parker tube
appears to deform to a greater extent during normal use than other endotracheal tubes.
This study aimed to investigate the resistance to gas flow that both the Mallinckrodt RAE
and Parker Flex-Tip demonstrate, and how these two types of tubes may differ in their
ability to withstand the deformation caused by thermosoftening and clinical positioning
during normal use.
Methods:
Mallinckrodt RAE (Mallinckrodt Medical, Dublin, Ireland) and Parker Flex-Tip
(Parker Medical, Highlands Ranch, CO) cuffed nasal endotracheal tubes, sizes 4.0, 4.5,
5.0, 5.5, 6.0, 7.0, 7.5 were connected to two Certifier FA Plus high flow modules (TSI
Incorporated, Shoreview, MN), one connected to the proximal and the second, via a 90°
fitting, to the distal end of each tube. A precise gas flow of 6 L/min was confirmed and
measurements of pressure were collected at both ends of each tube as each tube was bent
to angles of 70, 60, 50, and 45 degrees.
ii
Statistical analysis was done using a repeated measures analysis of variance and
making a Satterthwaite adjustment to degrees of freedom to eliminate any bias due to
heteroscedasticity. The alpha level was set at 0.05.
The three main effects found were the brand of the tube, the internal diameter of
the tube, and the degree of bend of the tube.
Results:
None of the two-way interactions tested was found to be statistically significant
(P≥0.198) (Table 1). However, the Parker Flex-tip nasal endotracheal tube, when
compared to the Mallinckrodt RAE tube, demonstrated a statistically significant higher
resistance to gas flow, at 98°F, over the entire range of tube diameters tested at both 50°
and 60° bends (P=0.013) (Table 2) (Figure 4).
Conclusion:
As is to be expected, smaller diameter nasal endotracheal tubes are associated
with an increased resistance to gas flow. Interestingly, the resistance to gas flow was
shown to be greater in the Parker Flex-tip nasal endotracheal tube under the conditions of
our testing. When used properly, the Parker Flex-tip nasal endotracheal tube has been
shown to cause less trauma and epistaxis during routine naso-tracheal intubation.
However, the increased resistance to gas flow may have a negative impact on the
physiologic work of breathing in nasally intubated patients; particularly in the smaller
size tubes used in the pediatric population. The physiological impact of this in terms of
iii
the increased work of breathing that may be required through a Parker tube warrants
further investigation.
iv
Acknowledgments
I would like to acknowledge Drs. Simon Prior, William Johnston, and William
Brantley for the time and effort they have given to this research project. A special thank
you to Dr. Simon Prior for his help and guidance, not only on this research project, but
throughout my anesthesia residency. I would also like to acknowledge Matthew Gray,
Biomedical Electronics Technician at the Wexner Medical Center, for his expertise and
assistance in the design and execution of our experiments.
v
Vita
January 21, 1984.......................................... Born in Bellefontaine, Ohio
2006 ............................................................ B.S. Exercise Science, Miami University
2011 ............................................................ D.D.S., The Ohio State University
2011 to present ........................................... Dental/Maxillofacial Anesthesiology
Residency, The Ohio State University
College of Dentistry
Fields of Study
Major Field: Dentistry
Minor Field: Anesthesiology
vi
Table of Contents
Abstract .......................................................................................................................... ii
Acknowledgments ........................................................................................................... v
Vita ................................................................................................................................ vi
Table of Contents .......................................................................................................... vii
List of Tables ............................................................................................................... viii
List of Figures ................................................................................................................ ix
Chapter 1: Introduction .................................................................................................. 1
Chapter 2: Methods ......................................................................................................... 5
Chapter 3: Results ......................................................................................................... 10
Chapter 4: Discussion ................................................................................................... 12
Chapter 5: Conclusion ................................................................................................... 15
Appendix A: Tables ...................................................................................................... 16
Appendix B: Figures ..................................................................................................... 19
References .................................................................................................................... 22
vii
List of Tables
Table 1: Resistance Data: R = pressure/flow ..................................................................16
Table 2: AVONA Data ..................................................................................................17
Table 3: Tukey Pairwise Comparisons ..........................................................................18
viii
List of Figures
Figure 1: Clinical Deformation of the Nasal Endotracheal Tube....................................19
Figure 2: Experimental Set-up ......................................................................................20
Figure 3: Grid for Experimental Measurements ............................................................20
Figure 4: Bar Graph – Comparisons of Resistance ........................................................21
ix
Chapter 1: Introduction
Nasal endotracheal intubation is preferred for several reasons by both oral and
dental surgery providers. Foremost among them, it allows unobstructed access to the oral
cavity. It also permits free movement of the mandible and maxilla during orthognathic
surgery, and significantly minimizes the possibility of having the tube unintentionally
damaged or displaced during treatment. Nasal endotracheal tubes are manufactured with
thick-walled, medical grade, polyvinyl chloride, much the same as oral endotracheal
tubes. They are, however, subject to many forms of thermosoftening: exposure to body
temperature, increased ambient temperature, and even intentional softening by the
anesthesiologist prior to intubation. Placement in warm saline, blanket warmers, or next
to a heated anesthetic vaporizer are common practices seen clinically. Thermosoftening
characteristics of nasal endotracheal tubes improve navigability of the tube through the
nasal passages and reduce damage to nasal mucosa and epistaxis.1
The nasal cavity is a fragile environment covered with a sensitive and well
perfused epithelium. It has a particularly variable anatomical structure and one that is
very difficult to visualize during the routine passage of a nasal endotracheal tube.2 The
common result being that nasal epistaxis is often observed during nasal intubations.
Although the above mentioned characteristics and practices of thermosoftening do
provide benefits, the structural integrity of the tubes may be undermined and cause
1
changes to the flow characteristics of gases; most notably, increases in resistance and
therefore work of breathing. Furthermore, the materials and processes by which nasal
endotracheal tubes are constructed differ between manufacturers, and perhaps to such an
extent that even standard clinical use may have different effects on the breathing
environment
Flow can be described as the volume of gas passing a cross sectional area per unit
of time, with the two main patterns of flow being laminar and turbulent. Endotracheal
tubes, whether oral or nasal, exhibit both types of flow with increasing amounts of
turbulent flow attributed to curvatures in the tube.3 In particular; nasal endotracheal tubes
are designed to approximate the anatomical path of the nose and pharynx. As a result,
they have a distinctive curvature as part of their design. The Hagen-Poiseuille equation
states that resistance varies inversely to the fourth power of the radius. However, this
relation applies only to laminar flow. At gas flows and tube diameters that we use
clinically the flow is assumed to be turbulent. Therefore, the resistance of nasal
endotracheal tubes must be determined empirically.4,5 Based on previous experiments,
resistance can be calculated by dividing the gas pressure by the flow rate. Resistance is
expressed in cm H2O/L/sec.3,6,7
Changes in the internal diameter of nasal endotracheal tubes do occur during
clinical use as a result of thermosoftening and manipulation. The preformed bend of
nasal endotracheal tubes is an area of concern. It has been noted clinically that this
particular area of the tube does not hold its original circular form and tends to collapse in
on its self, decreasing the internal diameter of the tube. The Parker Flex-Tip nasal
2
endotracheal tube is a recent addition to the anesthesiologist’s selection of intubating
tubes and brought with it a unique and very advantageous design of its distal tip
(navigating end). However, regular use of this particular nasal endotracheal tube for oral
and maxillofacial surgeries has revealed a tendency of this tube to collapse at its
preformed bend as the tube exits the nasal cavity (Figure 1). In comparison, one type of
nasal endotracheal tube may be more capable of withstanding the manipulation and
changes that occur with thermosoftening and clinical use.
With a reduction in the internal diameter of endotracheal tubes, an increased
resistance to gas flow is observed. The effect varies for different sizes of tubes and is
seen more profoundly in smaller sized endotracheal tubes, such as those used in pediatric
anesthesia. This increased resistance may result in an increased work of breathing and
place a considerable load on the respiratory muscles.8,9 In the general surgery situation
this would be seen most notably during spontaneous breathing trials, assessing whether or
not patients are ready to be weaned off mechanical ventilation. In dentistry, it is not
uncommon to have intubated patients breathing spontaneously for the entire duration of
the case. The implications of such influences on the work of breathing may be even more
pronounced in patients with conditions such as asthma and COPD. Additionally, should
this increased resistance prove to be clinically significant, the greater compliance of the
pediatric thorax may result in adequate gas exchange being affected.9,10 For these
patients, the extra work of breathing needed to overcome the increased resistance from
thermosoftened and collapsed endotracheal tubes could lead to problems with
spontaneous ventilation.
3
Both Parker Flex-Tip and Mallinckrodt RAE tubes are commonly used for nasal
intubations. While being clinically useful, nasal intubations typically require choosing a
smaller sized tube than the anesthesiologist may use for the same patient being orally
intubated. The combination of smaller tube size and the inherent curvature of the nasal
endotracheal tube increase the probability that thermosoftening will affect the structural
integrity of the tube. We wished to investigate the resistance to gas flow that both the
Mallinckrodt RAE and Parker Flex-Tip demonstrate, and how these two types of tubes
may differ in their ability to withstand the deformation caused by thermosoftening and
clinical positioning. This was done by testing the flow characteristics of oxygen through
the tubes under simulated clinical conditions. Our null hypothesis is that there is no
statistically significant difference in the resistance to gas flow between the Parker FlexTip and Mallinckrodt RAE at a temperature and degree of bend found clinically.
4
Chapter 2: Methods
Experimental:
Mallinckrodt RAE (Mallinckrodt Medical, Dublin, Ireland) and Parker Flex-Tip
(Parker Medical, Highlands Ranch, CO) cuffed nasal endotracheal tubes of the sizes 4.0,
4.5, 5.0, 5.5, 6.0, 7.0, 7.5 were used for testing in this study. One tube of each size was
stored in a 22.2°C (72°F) room for 24 hours prior to testing. Each tube was kept in its
original packaging and no manipulation of the tube was done prior to removal from its
package. All tests were conducted using a GE Datex-Ohmeda Excel 210 SE anesthesia
machine connected to a central oxygen source. Rubber circuit module test plugs were
placed in lieu of a breathing bag and to block the expiratory limb of the anesthesia
machine. The oxygen flowmeter was set to 6 L/min. Subsequently, the adjustable
pressure-limiting valve was adjusted to maintain a circuit pressure of 70 cm H2O
throughout our tests.
Two Certifier FA Plus high flow modules (TSI Incorporated, Shoreview, MN)
with corresponding digital interfaces were used to conduct our tests. Both of the high
flow modules were calibrated by a biomedical electronics technician prior to use. The
settings of the two digital interfaces were adjusted to allow analysis of the flow and
pressure of oxygen. The high flow modules were in-line positioned such that they
followed the correct flow of gas indicated by the blue label “FLOW →” on the front of
5
the module. The first high flow module (HFM1) was connected to the inspiratory limb of
the anesthesia machine with a 48-inch reusable corrugated breathing circuit tube. The
distal port of HFM1 was connected to an airway pressure fitting and the corresponding ¼
inch diameter silicone pressure tubing was connected to the positive pressure port of the
high flow module (Figure 2). The second high flow module (HFM2) was fitted with the
same airway pressure fitting and tubing on its proximal port with the distal port left open
to the atmosphere (Figure 2).
The first Mallinckrodt Nasal RAE tube to be tested was removed from its package
and cut with scissors at a mark two centimeters proximal to the cuff of the tube. This was
done to provide a uniform circular tip to all of the tubes and to remove the possibility of
the cuffed portion of the tube interfering with the set-up. The cuffed portion of the tube
that was removed was then discarded. The distal end of our remaining RAE tube was
then secured to a 90° fitting with black electrical tape (Figure 3). The tubes were
positioned carefully, making sure that the open end of the tube did not contact the fitting
and obstruct the flow of oxygen. Once secured, the tube was connected to the two high
flow modules with the proximal end of the tube connected to HFM1 and the distal end,
with the 90° fitting, connected to HFM2. A precise flow of 6 L/min was confirmed via
the digital interface. All measurements for use in our statistical analysis were collected
from HFM1. HFM2 was used to check for consistent, unobstructed flows of gas and to
confirm that the length of the tube distal to the preformed bend did not have any
influence on the pressure and flow measurements.
6
A grid with angles of 70, 60, 50, and 45 degrees was constructed on white poster
board and used to systematically manipulate the tubes to pre-marked angulations for each
measurement of flow and pressure (Figure 3). Each of 14 different tubes we tested comes
from the manufacturer pre-formed at a slightly different angulation. Therefore, our initial
measurement was done at this “out of package” angulation and not manipulated. Each
subsequent measurement was done with the tube manipulated to the pre-marked
angulations described above. The tube was secured at each angulation with pins to allow
sufficient time for the tube to conform to its new position and to obtain accurate
measurements. As a result, there were five measurements of pressure and flow for the
RAE tube being tested at 22.2°C. This same process was repeated for each size of RAE
and Parker Flex-Tip tube. Measurements of pressure and flow were collected three
separate times for each tube in order to calculate a mean pressure and identify any
obscure pressure measurements.
A new assortment of the same tubes (size and type) as described previously was
used for our second series of tests. Again, the tubes were stored at 22.2°C for 24 hours
and subsequently cut 2 centimeters proximal to the cuff prior to testing. This series of
tubes was then suspended in a 36.7°C (98°F) water bath for at least five minutes. After
the minimum five minutes, the tube to be tested was removed from the water bath and the
desired 36.7°C temperature of the tube confirmed using a laser thermometer. Our
requirement for testing was a tube temperature between 35°C and 37.8°C. If at any time
during the experiment the temperature of the tube was not within our designated range, it
was placed back into the water bath for at least two minutes until the desired temperature
7
was reached again. Measurements of pressure and flow for the warmed 36.7°C tube were
collected using the same method and angulations described for those tubes tested at
22.2°C.
Resistance to gas flow is an important component in the equation of physiologic
work of breathing. Our collected pressure and flow data was used in each case to
calculate resistance by dividing the mean of our three measurements of pressure by flow
as described by Manczur6 and Wright7.
Statistical:
Although multiple sets of data were collected, the purpose of our study was to
analyze only that data set determined as best representative of usual clinical conditions.
As a consequence, the pressure data only at the temperature of 98°F and at bends of 50°
and 60° was analyzed. This was done using a repeated measures analysis of variance.
This incorporated the method of using maximum likelihood estimates for the variances
and making a Satterthwaite adjustment to degrees of freedom to eliminate any bias due to
heteroscedasticity. The alpha level was set at 0.05. The three main effects were the
brand of the tube, the internal diameter of the tube, and the repeated factor, the degree of
bend in the tube.
Further, this ANOVA tested the statistical significance of every possible two-way
interaction of these three main effects. The analysis was done using the MIXED
procedure in SAS® Proprietary Software 9.2 (SAS Institute Inc., Cary, NC, USA).
8
Tukey pairwise comparisons were used whenever a significant effect was found
involving more than one degree of freedom in the effect.
9
Chapter 3: Results
All of the calculated values of resistance are presented in Table 1. The subset of
data that was used for our statistical analysis has been highlighted.
None of the two-way interactions tested was found to be statistically significant
(P≥0.198) (Table 1).
However, the Parker Flex-tip nasal endotracheal tube, when compared to the
Mallinckrodt RAE tube, demonstrated a statistically significant higher resistance to gas
flow, at 98°F, over the entire range of tube diameters tested at both the clinically
representative 50° and 60° bends (P=0.013) (Table 2) (Figure 4).
A statistically significant difference was also detected between the mean
resistance to gas flow between the two bends (P=0.020) (Table 2). This was
demonstrated for both brands of tubes and over all diameters tested. The resistance to gas
flow at a bend of 60° was higher than the resistance to gas flow at a bend of 50° (Figure
4).
Finally, a statistically significant difference between the mean resistance to gas
flow at the various diameters (P<0.001) was found for both brands of tubes and the two
bends tested (Table 2). As the diameter of the tube decreases, the resistance to gas flow
increases (Figure 4).
10
Our Tukey pairwise comparison of the effect ‘diameter’ is shown in Table 3. ‘Rchange’ is the difference in the average resistance to gas flow of ‘Diameter B’ compared
to ‘Diameter A’. Nasal endotracheal tubes, in general, demonstrate a difference in
resistance to gas flow with incremental decreases in diameter (5.0 to 4.5, 4.5 to 4.0 etc.).
A statistically significant change in resistance is revealed in the smaller diameter tubes.
5.5 to 5.0 (P=0.002). 5.0 to 4.5 (P=0.001). 4.5 to 4.0 (<0.001). This change in resistance
to gas flow between incremental sizes becomes non-significant at diameters 6.0 and
greater.
11
Chapter 4: Discussion
Based on our results, the Parker Flex-tip nasal endotracheal tube, when compared
to the Mallinckrodt RAE, demonstrated higher resistance to gas flow, at 36.7°C (98°F),
over the range of tube diameters tested at both 50° and 60° bends. We found, however,
that the difference in the mean resistance to gas flow between the two brands was
independent of either bend and/or diameter. This may have been due to the fact that such
a dependency does not exist, but we also have to recognize the possibility that our limited
initial experimental design may not have been able to identify either or both of these
dependencies. A larger sample size and/or further testing of our collected data may
elucidate such interactions if they exist.
As is to be expected, smaller diameter nasal endotracheal tubes are associated
with an increased resistance to gas flow following the principles and experiments
described by Mitchell3, Manczur6, Wright7, and El-Khatib8. Interestingly, the resistance
to gas flow was shown to be greater in the Parker Flex-tip nasal endotracheal tube in all
comparisons under the conditions of our testing. The physiologic implications of this
difference may be of a magnitude worth investigating further. Should this difference be
physiologically interesting, then this would logically be of particular importance for
spontaneously ventilating pediatric patients or those with respiratory conditions such as
asthma or COPD. It has been suggested that the presence of a nasal endotracheal tube
12
may doubles the work of breathing in chronically intubated adults and lead to respiratory
failure in certain children and infants.11 Furthermore, in vivo measurements of resistance
are generally higher than in vitro measurements, perhaps because of secretions, head and
neck positioning, or increased turbulence. Based on this information, it seems
appropriate to question how great the impact of this increased resistance to gas flow is in
the smaller diameter nasal endotracheal tubes when these other factors are taken into
consideration.
Often times the anesthesiologist is presented with a choice between two different
sizes of nasal endotracheal tube. Does he/she choose the larger size tube that will allow
higher volumes of unobstructed gas flow at the expense of traumatizing the fragile
epithelium of the nasal cavity? Or is the smaller size tube chosen in an attempt to reduce
possible injury or irritation at the expense of higher resistance to gas flow and respiratory
compromise? Based on our results, this decision does not have as many potential
implications when choosing between incremental sizes that are larger than 6.0. However,
when dealing with tubes that are smaller than 6.0, the decision potentially weighs more
heavily on respiratory physiology, and perhaps more so when using a Parker Flex-tip
nasal endotracheal tube.
That the material used in the Parker Flex-tip naso-tracheal tube is slightly more
prone to deformation may be suggested by the manufacturer’s later decision to package
these tubes in pre-formed cases; an attempt to maintain the original shape and deter any
manipulation of the tubes that may compromise structural integrity prior to immediate
clinical use.
13
When used properly, the Parker Flex-tip nasal endotracheal tube has been shown
to cause less trauma and epistaxis during routine naso-tracheal intubation. Our study has
shown however, a statistically significant difference in its resistance to gas flow
compared to the Mallinckrodt RAE under simulations of relevant clinical situations, with
the Parker Flex-tip showing the higher resistance, especially in the smaller sizes. In vivo
investigations would now be valuable to determine if the higher resistance to gas flow
that we found in the Parker-Flex tip tube has a negative impact on the physiologic work
of breathing in nasally intubated patients; particularly in the smaller size tubes used in the
pediatric population. It may be, that despite the statistically significant difference
demonstrated between Parker Flex-tip and Mallinckrodt RAE tubes in the bench top
situation, that both brands still provide adequate flow of gas despite undergoing
deformation from thermosoftening and clinical positioning. However, knowing that the
pediatric population has a higher thoracic compliance, it seems plausible that there would
be greater sensitivity to the impact of the higher resistance to gas flow that the Parker
Flex-tip demonstrates, and this existing uncertainty warrants further investigation.
14
Chapter 5: Conclusion
Parker Flex tip and Mallinckrodt RAE nasal endotracheal tubes are commonly
used in the dental surgery setting. This experiment has shown that the resistance to gas
flow is different between the two brands of tubes, with the Parker Flex-tip demonstrating
higher resistance to gas flow under clinically relevant situations. Further testing should
be done to determine the physiologic impact of our findings.
15
Appendix A: Tables
Ø (mm)
Tube
Temp
Bend
7.5
7.0
6.0
5.5
5.0
4.5
4.0
RAE
72°
As received
0.061
0.075
0.105
0.116
0.162
0.221
0.338
45°
0.065
0.077
0.107
0.122
0.167
0.236
0.350
50°
0.068
0.078
0.110
0.123
0.171
0.241
0.366
60°
0.069
0.078
0.114
0.130
0.182
0.254
0.364
70°
0.071
0.080
0.117
0.137
0.199
0.295
0.394
As received
0.066
0.074
0.104
0.116
0.163
0.221
0.342
45°
0.068
0.077
0.107
0.121
0.168
0.237
0.355
50°
0.068
0.078
0.110
0.124
0.183
0.262
0.367
60°
0.069
0.079
0.115
0.132
0.192
0.279
0.365
70°
0.071
0.081
0.117
0.138
0.200
0.307
0.395
As received
0.066
0.075
0.106
0.116
0.169
0.241
0.342
45°
0.068
0.078
0.111
0.123
0.178
0.250
0.352
50°
0.069
0.081
0.113
0.125
0.180
0.264
0.368
60°
0.072
0.081
0.120
0.132
0.189
0.279
0.382
70°
0.077
0.091
0.125
0.142
0.207
0.301
0.421
As received
0.066
0.076
0.107
0.117
0.171
0.242
0.342
45°
0.069
0.079
0.114
0.123
0.184
0.254
0.360
50°
0.070
0.082
0.119
0.127
0.197
0.268
0.381
60°
0.074
0.086
0.124
0.137
0.204
0.298
0.426
70°
0.079
0.098
0.131
0.149
0.216
0.334
0.471
RAE
Parker
Parker
98°
72°
98°
Table 1: Resistance Data: R = pressure/flow. Units = (cmH2O)/(L/sec). Ø = Diameter
16
Type 3 Tests of Fixed Effects
Num
Den
DF
DF
Effect
F Value
Pr > F
Tube
1
4.3
16.67
0.0130
Diameter
6
4.3
860.53
<0.0001
Bend
1
6
9.88
0.0200
Tube*Diameter
6
4.3
2.24
0.2169
Tube*Bend
1
6
2.09
0.1983
Diameter*Bend
6
6
1.03
0.4863
Table 2: AVONA Data: alpha = 0.05
17
R-change (cm
Diameter A (mm)
Diameter B (mm)
AdjP
H2O)/(L/sec)
4
4.5
0.65
<.001
4
5
1.14
<.001
4
5.5
1.53
<.001
4
6
1.61
<.001
4
7
1.82
<.001
4
7.5
1.88
<.001
4.5
5
0.50
0.001
4.5
5.5
0.88
<.001
4.5
6
0.96
<.001
4.5
7
1.17
<.001
4.5
7.5
1.24
<.001
5
5.5
0.38
0.002
5
6
0.46
0.001
5
7
0.68
<.001
5
7.5
0.74
<.001
5.5
6
0.08
0.386
5.5
7
0.29
0.005
5.5
7.5
0.36
0.002
6
7
0.21
0.018
6
7.5
0.28
0.006
7
7.5
0.07
0.519
Table 3: Tukey Pairwise Comparisons
(Pairwise comparisons of mean resistance to gas flow between each size of endotracheal
tube tested. The underlined data shows the incremental size comparisons that were most
relevant for our study.)
18
Appendix B: Figures
Figure 1: Clinical Deformation of the Nasal Endotracheal Tube
(Clinical placement of a size 5.5 Parker Flex-tip nasal endotracheal tube demonstrating
the collapse that occurs at the preformed bend due to thermosoftening. The picture on the
left was taken within minutes of initial intubation. The picture on the right was taken 30
minutes after intubation.)
19
Figure 2: Experimental Set-up
(Experimental set-up demonstrating the connection of the endotracheal tube to the two
high flow modules.)
Figure 3: Grid for Experimental Measurements
(Close up view of the grid placed behind the endotracheal tube to allow measurements to
be taken at our predefined degrees of bend.)
20
Figure 4: Bar Graph – Comparisons of Resistance
(Bar graph representing the difference in resistance to gas flow between the two brands of
tube tested at 98°F. Each ‘P’ represents the Parker Flex-tip and each ‘S’ represents the
standard tip (Mallinckrodt RAE) at the corresponding diameter and degree of bend.
21
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3.
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4.
Hendrick HHL. Comparative study of the different factors influencing resistance
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