SUPPLEMENTAL DIGITAL CONTENT
AN
IN-VITRO
STUDY
TO
ASSESS
DETERMINANT
FEATURES ASSOCIATED WITH FLUID SEALING IN THE
DESIGN
OF
ENDOTRACHEAL
TUBE
CUFFS
AND
EXERTED TRACHEAL PRESSURES
Gianluigi Li Bassi, MD; Otavio Tavares Ranzani, MD; Joan Daniel Marti, RPT;
Valeria Giunta, MD; Nestor Luque, MD; ValentinaIsetta, BSEBE; Miguel Ferrer, MD,
PhD; Ramon Farre, PhD; GuilhermeLeite Pimentel, BSEBEand Antoni Torres, MD,
PhD.
MATERIALS AND METHODS
This study was conducted at the laboratories of the pneumology department, Hospital
Clinic and University of Barcelona, Barcelona, Spain. The protocol was approved by
the Institutional Review Board and Ethics Committee. Table 1 of the main manuscript
depicts the study experimental design. The cuffs of 8 endotracheal tube (ETT) types
with internal diameters of 7.0, 7.5 and 8.0 mm (I.D.) with a cylindrical or tapered
shape made of polyvinylchloride (PVC) or polyurethane were studied.
Cuffs characteristics
Outer diameter: As previously reported (1), the cuff’s largest outer diameter (O.D.) of
each 7.0, 7.5 and 8.0 mm I.D. tube was randomly measured 3 times using a sliding
caliper and stepwise cuff inflation to 15, 20, 25 and 30 cm H2O through a cuff
pressure regulation system (2). The pressure regulation system was calibrated prior to
the beginning of the study. A new tube was used for each measurement. Additionally,
we computed the cuff cross sectional area (CSA) and the ratios between the cuff and
tracheal model CSA.
Length: The cuff length of each 7, 7.5 and 8 mm I.D. tube was randomly measured 3
timeswith a sliding caliper and cuff inflation to 20 cm H2O. A new tube was used for
each measurement. We computed the cuff O.D.-length ratio.
Compliance: The cuff compliance of each 7, 7.5 and 8 mm I.D. tube was randomly
assessed 3 times and a new tube was used for each measurement. Following complete
removal of the residualgas, the internal cuff pressure was increased up to 40 cm H2O
through manual stepwise increments of 1 ml of air via a 1-ml graduated 50-mL
syringe connected through a 3-way stopcock to the pilot balloon. The tested cuff
wasalso connected to a pressure transducer (MPX 2010 DP; Motorola, Phoenix, AZ,
USA) to record pressure signals on a personal computer for subsequent analysis with
dedicated software (Colligo; Elekton, Milan, Italy). Cuff compliance was computed
through the analysis of the straight portionsof the pressure-volume curve (internal cuff
pressure range: 15-40 cm H2O). Additionally, the cuff compliance within the tracheal
model was similarly assessed.
Oropharyngeal Secretions Simulant
Based on preliminary studies (3) which assessed viscosity of oropharyngeal secretions
in pigs on prolonged mechanical ventilation, we devised artificial oropharyngeal
secretions with a viscosity of 3 centipoise at a shear rate of 75 sec-1. We added 50 mg
of polyethylene oxide powder (Polyox Water Soluble Resin Coagulant NF; Dow
Chemical Company; Cary, NC) into 100 mL of boiling distilled water. Afterward, the
solution was removed from the heat, stirred for two hours and then stored for future
use.
Short-term fluid-sealing efficacy
We randomly assessed the sealing properties of each 7.0, 7.5 and 8.0 mm I.D. ETT
type cuff within 32–cm long PVC tracheal models of 18, 20 and 22 mm I.D.,
respectively. We tested sealing efficiency at an internal cuff pressure of 15, 20, 25 and
30 cm H2O. Each test was repeated three times and a new ETT was used for each test.
Figure 1 in the main manuscript depicts the in-vitro settings to measure leakage. The
tracheal model was oriented 30 degrees above horizontal. To maintain the internal
cuff pressure, the cuff pilot balloon was connected to a pressure regulation system (2).
To prevent immediate leakage as the oropharyngeal secretions simulant was poured
into the tracheal model we increased the internal cuff pressure up to 40 cm H2O, and
we regulated the positive end expiratory pressure (PEEP) valve (4 VENT 22M,
Rüsch-Teleflex Inc., Limerick, PA, USA) of the ventilatory circuit until air
leakageacross the cuff developed. Next we poured artificial oropharyngeal secretions
to achieve a 10-cm column above the ETT cuff while the tracheal model was held
vertically. At the beginning of the test, the circuit was disconnected and the internal
cuff pressure was decreased to the randomized pressure. The test was carried out until
all fluids leaked across the cuff or until the 1 hour test period ended.Simulant leakage
is reported as the average fluid flow rate across the cuff and wascomputed by dividing
the volume of fluid collected by either 60 min or the time at which all fluid had leaked.
A completed 1-hour leakage test was defined as an experiment in which the simulant
did not entirely leak within 1 hour.
Long-term fluid-sealing efficacy
Based on the results of the short-term leakage study, the 4 best-performing ETT types
were tested for a longer period. Using aforementioned methods we randomly tested
7.5-mm I.D. ETT types for 24 hours within 20-mm I.D. tracheal model at an internal
cuff pressure of 30 cm H2O. Each test was repeated three times and a new ETT was
used for each test.
Tracheal wall pressure exerted by the cuff
We used methods previously validated by Horisberger et al (4). An intracranial
pressure sensor probe (Codman,Raynham, MA, USA) was placed between the cuff’s
surface and the tracheal models to assess cuff pressure transmitted against the tracheal
wall (Twp). Cuffs of 7.0, 7.5 and 8.0 mm I.D. ETTs were randomly tested within 18,
20, 22 mm I.D. tracheal models, respectively. Each test was repeated 3 times and a
new tube was used for each test. After complete deflation of the cuff, its pilot balloon
was connected via a three-way stopcock to a 50-ml syringe providing a continuous air
flow of 3.33 mL/min via an automatic syringe-pump (Alaris GH, Cardinal Health,
Dublin, OH, USA), and a pressuretransducer (MPX 2010 DP; Motorola, Phoenix, AZ,
USA)to monitor and record the internal cuff pressure. All pressure signals were
recorded on a computer for subsequent analysis with dedicated software (Colligo;
Elekton, Milan, Italy). During the test, the internal cuff pressure was progressively
increased to achieve a Twp of 40 cm H2O then the pressure waveforms were analyzed
to specifically assess transmitted Twp at 15, 20, 25 and 30 cm H2O of internal cuff
pressures. Supplemental Figure 1 shows calculation of Twp through the recorded
waveforms.
Tracheal wall pressure mapping
To assess regional distribution of Twp, we used an acrylic 21-mm I.D. cylindrical
tracheal model, with a 1-mm thick, 50-mm wide and 64-mm long pressure sensor
(TactArray Pressure Sensor, Conductive Cloth, range 0-140 cmH2O, PPS, Los
Angeles, CA, USA) which covered 76% of the tracheal model internal circumference.
The Twp patterns were acquired and analyzed using dedicated software (PPS
Chamelon TVR Software, v. 1.3.9.2-2010, PPS, Los Angeles, CA, USA). Prior to the
beginning of the study the sensor was properly calibrated. During the test, to assure a
correct alignment of the ETT cuff into the tracheal model, the ETT was placed within
a plastic sleeve and a straightening rod was inserted into its lumen. The ETT pilot
balloon was connected to the cuff pressure regulation system (2). The distribution of
the Twp was recorded for each 7.5 mm I.D. ETT type upon stepwise inflation of the
cuff to 15, 20, 25 and 30 cm H2O. Each test was randomly performed and repeated
three times. The cuff-trachea contact area and the percentage of Twp distribution
measurements lower than the cuff pressure (between 31-40, 41-50 and greater than 50
cmH2O) were computed and analyzed.
Statistical analysis
Randomization: The randomized list of 72 tests to assess each of the cuff’s structural
features (outer diameter, length and compliance) was developed by creating a list of
of possible combinations for each of the 8 tubes per 3 ETT I.D. and 3 levels of
replications. A uniformly distributed list of random numbersbetween 0.00000 and
1.00000 was generated and added to the data set. Then the list of combinations was
sorted by level of replication and random numbers. The randomized list of 288 cuff
short-leakage tests was developed by creating a list of possible combinations for each
of 8 tubes per 3 ETT I.D., per 4 internal cuff pressures and 3 levels of replications. A
uniformly distributed list of random numbers between 0.00000 and 1.00000 was
generated and added to the data set. Then the list of combinations was sorted by level
of replication and random numbers. The randomized list of the 9 long-term leakage
tests was developed creating a list of combinations of the 3 tubes and 3 levels of
replications. A uniformly distributed list of random numbers between 0.00000 and
1.00000 was generated and added to the data set. Then the list of combinations was
sorted by random numbers. The 3 tests to assess long-term sealing efficacy of the HiLoTM endotracheal tube were carried out following the first revision of the manuscript.
The randomization list of the 72 transmitted Twp was developed while creating a list
of combinations for the 8 tubes per 3 ETT I.D. and 3 levels of replications. A
uniformly distributed list of random numbersbetween 0.00000 and 1.00000 was
generated and added to the data set. Then the list of combinations was sorted by level
of replication and random numbers. The randomized list of the 24 Twp pressure
mapping tests was developed while creating a list of combinations for the 8 tubes and
3 levels of replications. A uniformly distributed list of random numbers between
0.00000 and 1.00000 was generated and added to the data set. Then the list of
combinations was sorted by level of replication and random numbers.
Categorical and continuous data are presented as percentage and as mean±SD
(ormedian and interquartile range [IQR]), respectively. Continuous variables were
analyzed using the Kruskal-Wallis test or Friedman test, and the Mann-Whitney Utest or Wilcoxon signed rank test for post-hoc multiple comparisons. Each pair-wise
comparison was corrected using Bonferroni methods. Chi-square test was applied for
comparisons of categorical variables. As for the Twp distribution analysis, the
percentages of Twp within the predefined ranges were considered as continuous
variables. Univariate linear regression analyses were used to evaluate the association
between cufffeatures and leakage flow rate. All significantly associated variables
were included into themultivariate regression analysis with a stepwise model selection
procedure in order to preventmulticollinearity. Variables with a p-value >0.10 were
eliminated from the final model. Pearson correlation was used to assess the
association between mean cuff length assessed outside and within the tracheal model,
and the Twp obtained via different methods. A two-sided p value<0.05 was
consideredstatistically significant. All statistical analyses were performed using SPSS
software (version 13.0; IBM, Chicago, IL, USA).
Reference List
1. Bernet V, Dullenkopf A, Maino P, et al.: Outer diameter and shape of paediatric
tracheal tube cuffs at higher inflation pressures. Anaesthesia2005; 60: 1123-8
2. Farré R, Rotger M, Ferre M, et al.: Automatic regulation of the cuff pressure in
endotracheally-intubated patients. EurRespir J 2002; 20: 1010-3
3. Li Bassi G, Marti JD, Jeuma N, et al.: Assessment of oropharyngeal secretions
viscosity during tracheal intubation: An experimental study Am J RespirCrit Care
Med 2011; 183: A5854
4. Horisberger T, Gerber S, Bernet V, et al.: Measurement of tracheal wall pressure: a
comparison of three different in vitro techniques. Anaesthesia2008; 63: 418-22
Supplemental Table 1. Cuff-Trachea contact areas (cm2) per internal cuff pressure.
Internal cuff pressure (cmH2O)
Endotracheal tube
15
20
25
30
Ruschelit® Safety Clear Plus
Hi-LoTM
Profile Soft-Seal®
SacettTM
TaperguardTM
Sheridan/HVT®
Kimvent* Microcuff*
SealGuardEvacTM
10.53 ± 8.4
13.83 ± 1.7
8.75 ± 0.4
11.80 ± 2.3
9.35 ± 1.0
12.25 ± 0.8
15.84 ± 2.6
14.29 ± 1.2
9.99 ± 5.2
15.21 ± 1.6
9.24 ± 0.4
11.81 ± 0.8
10.31 ± 0.8
13.03 ± 0.8
17.76 ± 0.7
14.60 ± 1.4
10.92 ± 4.2
15.37 ± 2.3
9.00 ± 1.0
12.49 ± 0.9
10.65 ± 0.6
13.08 ± 0.8
17.96 ± 0.8
14.68 ± 1.4
11.96 ± 3.1
17.29 ± 0.8
10.20 ± 1.0
12.47 ± 0.7
11.05 ± 0.7
11.99 ± 1.2
18.01 ± 0.7
15.00 ± 1.1
N: 96, Data are Mean±SD
Mean Cuff-Trachea
Contact Area (cm2)
10.85 ± 4.8
15.43 ± 1.9
9.30 ± 0.9
12.14 ± 1.2
10.34 ± 0.9
12.59 ± 0.9
17.39 ± 1.6
14.64 ± 1.1
Supplemental Table 2. Comparison of cuff length assessed inside vs. outside the artificial trachea
Endotracheal tube
Cuff Shape
Ruschelit® Safety Clear Plus
Hi-LoTM
Profile Soft-Seal®
SacettTM
TaperguardTM
Sheridan/HVT®
Kimvent* Microcuff*
SealGuardEvacTM
Cylindrical
Cylindrical
Tapered
Tapered
Tapered
Tapered
Cylindrical
Tapered
Cuff Length
Cuff Length
Outside Trachea*⌃
(mm)
Inside Trachea*⌃
(mm)
37.72
43.17
33.92
32.10
43.70
39.37
45.10
43.82
19.97
30.42
18.48
23.62
20.61
26.05
35.52
29.20
Cuff Length Inside Trachea
Cuff Length Outside Trachea
(%)
52.94
70.47
54.48
73.58
47.16
66.17
78.75
66.64
Internal cuff pressure 20 cm H2O; ⌃ Average value of 3 replicated assessments of 7.5 mm internal diameter endotracheal tube. Pearson’s Correlation:
8, r = 0.6497, p=0.0892
N:
SUPPLEMENTAL FIGURE 1
Supplemental Figure 1. Analysis of 7.0–mm internal diameter SealGuardEvacTM (Covidien-Nellcor™ and
Puritan Bennett™, Boulder, CO, USA) cuff-related transmitted tracheal pressure. Internal cuff pressure and
transmitted tracheal wall pressure waveforms were matched to assess the pressure assessed by the
intracranial pressure sensor probe, upon inflation of the endotracheal tube cuff. Transmitted tracheal
pressures at 15, 20, 25 and 30 cm H2O of the internal cuff pressures were computed.