British Journal of Anaesthesia 89 (2): 271±6 (2002)
Maintenance of stable cuff pressure in the BrandtTM tracheal
tube during anaesthesia with nitrous oxide
F. Karasawa*, T. Okuda, T. Mori and T. Oshima
Department of Anaesthesiology, National Defense Medical College, Tokorozawa, Saitama 359-8513, Japan
*Corresponding author
Background. The BrandtÔ tracheal tube keeps cuff pressure constant during anaesthesia, but
the mechanisms have not been examined. We assessed volume, pressure and gas concentration
in the cuff and pilot balloon using the BrandtÔ system.
Methods. The pressure in an air-®lled cuff of the BrandtÔ system (Mallinckrodt BrandtÔ tracheal tube, n=60) was recorded during anaesthesia with 67% nitrous oxide; gas volume and
concentration in cuffs and balloons were measured for up to 12 h from the start of anaesthesia.
The volume change of each gas was calculated to assess its contribution to the cuff pressure.
We also measured cuff compliance in vitro.
Results. Cuff pressure increased slightly during anaesthesia (P<0.05). The nitrous oxide
concentration increased to 47.7 (8.2)% (mean (SD)) in the cuff and to 2.2 (0.9)% in the pilot
balloon. The nitrous oxide volume in the cuff and pilot balloon increased by approximately 2
ml during the ®rst 4 h of anaesthesia. The carbon dioxide volume increased slightly, and
nitrogen and oxygen did not change signi®cantly. The compliance of the BrandtÔ tube cuff
was six times greater than that of a standard tube cuff (Mallinckrodt Hi-ContourÔ tracheal
tube).
Conclusions. The BrandtÔ tracheal tube maintains stable cuff pressure during nitrous oxide
anaesthesia because of a highly compliant balloon. The concentration gradient of nitrous oxide
between the cuff and pilot balloon also contributes to the stable-cuff pressure because the high
nitrous oxide concentration in the cuff reduces nitrous oxide in¯ux.
Br J Anaesth 2002; 89: 271±6
Keywords: anaesthetics gases, nitrous oxide; equipment, cuffs tracheal; equipment, tubes
tracheal
Accepted for publication: March 18, 2002
Nitrous oxide easily permeates polyvinyl chloride, the
material of tracheal tube cuffs, so that cuff pressure
increases during anaesthesia with nitrous oxide.1±3 To
avoid this, the cuff should be repeatedly de¯ated during
anaesthesia with nitrous oxide. Many methods are used
to prevent nitrous oxide diffusion and/or to improve
compliance, and reduce the complications of tracheal
intubation.4±8 Among them, the BrandtÔ system,9 which
has a large pilot balloon that facilitates ef¯ux of nitrous
oxide into the air, is a unique and reliable device to
avoid an increase in tracheal tube cuff pressure. It
seems to work by allowing nitrous oxide loss,9 10 but the
precise mechanisms remain unclear. We considered the
possibility that nitrous oxide concentrations in the
BrandtÔ tracheal tube cuff would be similar to those
in the standard tracheal tube, but that the nitrous oxide
concentration in the pilot balloon would be less because
of loss of nitrous oxide into the air, leading to a
concentration gradient of nitrous oxide between the cuff
and pilot balloon.
Compliance of the cuff determines cuff pressure
during anaesthesia because intra-cuff pressure depends
on the volume of gases in the cuff and cuff compliance.
Highly compliant cuffs limit the increases in cuff
pressure during anaesthesia with nitrous oxide.7
Because Brandt and Pokar9 reported that the pilot
Ó The Board of Management and Trustees of the British Journal of Anaesthesia 2002
Karasawa et al.
balloon of the system is thin, we hypothesized that the
high compliance of the BrandtÔ system contributes to
the stable-cuff pressure.
spectrometry (AMIS 2000, INNVISION A/S, Odense,
Denmark), which was calibrated with standard gases.
Data analysis
Methods
Correction of gas concentrations
Preparation of the subjects
After obtaining institutional approval and patients'
informed consent, patients (ASA physical status class I
or II) for elective surgery were studied. Patients who
smoked or those with symptoms of upper airway
irritation were excluded. Premedication with hydroxyzine
(50 mg) and atropine sulfate (0.5 mg) was given i.m. 1 h
before surgery. After breathing 100% oxygen, anaesthesia was induced with propofol (2±3 mg kg±1).
Vecuronium (0.1 mg kg±1) was then given to relax the
muscles. The trachea was intubated with the Hi-Contour
BrandtÔ tracheal tube (Mallinckrodt, Athlone, Ireland).
Tube size was 7.5 mm ID for females and 8.0 mm ID
for males. Lubricant was not used. The pilot balloon of
the tracheal tube was connected to a pressure transducer
through a three-way stopcock. The mean intra-cuff
pressure was measured every 10 min using a monitor
(AS3, Datex, Helsinki, Finland). The cuff was aspirated
as much as possible and then in¯ated with the lowest
volume of air that would not leak when the intra-airway
pressure was 18 cm H2O. The volume used to ®ll the
cuff and the initial sealing pressure was recorded.
Anaesthesia was maintained with 67% nitrous oxide
and 33% oxygen, supplemented with iso¯urane or
sevo¯urane, using a circle system (Excel 210,
Ohmeda, Madison, WI, USA). The lungs were ventilated
mechanically and end-tidal carbon dioxide was maintained within a physiologically normal range. The
concentration of the inspired gas mixture was monitored
using a multi-gas monitor (Capnomac UltimaÔ, Datex,
Helsinki, Finland). A humidi®er was used, but use of a
nasogastric tube was avoided.
The dead volume of the pilot balloon (Vdead[pb]) was
estimated at 1.3 ml (Appendix). Because Vdead[pb]
dilutes the concentration of each gas aspirated from
the cuff (Casp), the actual concentration of each gas in
the cuff should be corrected and was calculated using
the following formula:
(Casp3Vasp±Casp[pb]3Vdead[pb])/(Vasp±Vdead[pb]) (1)
where Vasp and Casp[pb] denote the volume aspirated from
cuffs and gas concentration in the pilot balloon, respectively.
Estimation of volume change of each gas
Because gas concentration in the cuff or pilot balloon is
affected by volume changes of other gases, volume change
of each gas is required to assess the contribution toward a
change in cuff pressure. The injected volume of each gas
was calculated using the following formula:
(Vinj+Vdead[cuff]+Vdead[pb])3Cair
(2)
where Vinj, Vdead[cuff], and Cair denotes injected volume,
dead volume of the cuff, and gas concentration in the air,
respectively. Vdead[cuff] was estimated at 0.2 ml
(Appendix). The aspirated volume of each gas was calculated using the following formula:
(Vasp[cuff]+Vdead[cuff])3Casp[cuff]
+(Vasp[pb]+Vdead[pb])3Casp[pb]
(3)
where Vasp[cuff], Vasp[pb], and Casp[cuff] denote the volume
aspirated from the cuff and pilot balloon, and gas concentration in the cuff, respectively. Consequently, the volume
change was Equation 22Equation 3.
Measurement of compliance in vitro
Experimental procedure
Intra-cuff pressure was measured every 10 min during
anaesthesia. Studies were completed at 0.5, 1, 2, 4, 8, and 12
h (group 0.5H, 1H, 2H, 4H, 8H, and 12H; n=10 for each). At
the end of the study, the connecting tube was clamped
approximately 2 cm from the pilot balloon and the pilot
balloon was aspirated as much as possible. The connecting
tube was then unclamped and the cuff was aspirated
separately from the pilot balloon. Approximately 15 min
later, the volume of aspirated gases was measured at room
temperature using a calibrated syringe, after the gases had
been ®rst compressed and then decompressed. We took the
mean value to avoid a possible error due to friction between
the barrel and piston of the syringe. The nitrous oxide
concentration was assayed using quadropole mass-
To assess the volume±pressure relationship of the
BrandtÔ system, the pilot balloon and the cuff of the
Hi-Contour BrandtÔ and the Hi-ContourÔ (n=5 for
each) tracheal tubes were in¯ated with air, 2 ml at a
time, using a syringe. Then the connection tubes of the
BrandtÔ tracheal tubes (n=5) were cut 2 cm from the
pilot balloon. The pilot balloon and the cuff were
in¯ated separately with air, 0.5 or 1 ml at a time. The
in¯ated volume and the intra-cuff pressure were
recorded. The Hi-ContourÔ tracheal tube is a standard
tracheal tube and has the same type and volume of cuff
as the Hi-Contour BrandtÔ tracheal tube. In addition,
the tracheal tube (n=5) was placed in an 18.2-mm
diameter glass tube (approximately the same crosssectional diameter as an adult female trachea), and the
272
Nitrous oxide concentration in the BrandtÔ tube cuff
Table 1 Patient details. Data are expressed as number of patients or mean (SD or range). The characteristics of the elapsed time groups were comparable
Gender (M/F)
Age (yr)
Weight (kg)
Height (cm)
0.5H
1H
2H
4H
8H
12H
5/5
58 (40±69)
60.8 (12.9)
160.6 (10.1)
5/5
67 (48±75)
52.3 (7.6)
155.1 (10.4)
5/5
53 (19±78)
59.5 (9.6)
159.8 (9.5)
5/5
65 (48±77)
51.6 (11.3)
153.1 (7.8)
5/5
64 (36±79)
56.2 (6.9)
153.6 (5.5)
5/5
58 (22±78)
56.6 (11.8)
160.8 (10.1)
Table 2 Cuff pressure, volume, and gas concentrations in the cuff and pilot balloon of the BrandtÔ system during anaesthesia with nitrous oxide. Data are
expressed as number of patients or mean (SD). The characteristics of the elapsed time groups were comparable. P values denote the probability of statistical
error in comparison among the different time groups. ns denotes no statistical signi®cance. *P<0.01 vs volume injected. ²P<0.01 vs values in the 0.5H group.
³
P<0.01 vs values in the 1H group. ¶P<0.01 vs values in the 2H group
Pressure (mm Hg)
Initial
>22
Volume (ml)
Injected
Aspirated
From cuffs
From balloons
Change
Concentrations (%)
Nitrous oxide
Cuffs
Balloons
Nitrogen
Cuffs
Balloons
Oxygen
Cuffs
Balloons
Carbon dioxide
Cuffs
Balloons
0.5H
1H
2H
4H
8H
12H
P value
15 (1)
0
15 (1)
0
14 (1)
1
14 (1)
0
14 (1)
1
14 (1)
1
ns
ns
33.9
34.1
5.0
29.1
0.2
33.9
34.3
5.2
29.1
0.4
33.7
35.6
5.3
29.8
1.4
32.3
34.7
5.1
29.5
2.2
33.4
34.7
4.5
30.7
1.8
33.6
35.5
4.4
31.0
1.8
ns
ns
ns
<0.05
<0.01
(2.5)
(2.1)
(1.6)
(1.1)
(1.5)
(2.5)
(2.6)
(2.0)
(1.5)
(1.5)
(2.8)
(3.8)*
(2.4)
(1.1)
(1.0)
(0.9)
(1.9)*
(1.6)
(1.4)
(1.2)
(1.6)
(1.9)*
(1.3)
(1.7)
(1.2)
(2.7)
(3.6)*
(1.6)
(2.3)
(1.8)
10.8 (4.1)
0.0 (0.1)
25.9 (8.5)²
0.4 (0.4)
33.4 (7.0)²
1.2 (0.9)²
42.7 (5.6)²³
1.4 (1.0) ²
45.5 (9.1)²³¶
1.6 (0.9)²³
47.7 (8.2)²³¶
2.2 (0.9)²³
<0.001
<0.001
67.0 (3.8)
78.2 (0.6)
55.4 (7.0)²
77.7 (0.7)
49.7 (5.8)²
77.2 (1.0)
41.7 (5.3)²³
76.9 (1.2)²
38.5 (7.7)²³¶
77.0 (0.9)
37.9 (6.4)²³¶
76.2 (1.0)²³
<0.001
<0.001
18.9 (0.9)
21.1 (0.6)
15.0 (2.2)²
21.0 (0.6)
12.8 (1.7)²
20.5 (0.5)
11.0 (2.2)²³
20.6 (0.6)
10.8 (4.3)²³
20.5 (0.6)
8.8 (3.0)²³¶
20.5 (0.5)
<0.001
ns
2.3 (0.4)
0.1 (0.0)
2.6 (1.1)
0.1 (0.1)
3.5 (0.7)
0.2 (0.1)
3.9 (1.1)
0.3 (0.3)
4.4 (2.0)²³
0.4 (0.6)
5.0 (1.2)²³
0.3 (0.2)
<0.001
ns
of the cuff or balloon was calculated as the reciprocal
of the gradient (i.e. elastance) of the relationship at 15
mm Hg.
Statistical analysis
Fig 1 Changes in the air-®lled cuff pressure of the BrandtÔ tracheal tube
(group 12H). During nitrous oxide anaesthesia, cuff pressure increased
slightly; the closed circle denotes a signi®cant increase in cuff pressure
(P<0.05 vs initial values). When anaesthesia was ®nished before the
completion of the study, the number of patients included in the statistical
analysis is shown by the marker of each point.
intact BrandtÔ system or cuff only was in¯ated with air
to measure the volume±pressure relationship in a
condition similar to the clinical situation. Compliance
Data were presented as the number of patients or mean (SD).
Two-way analysis of variance (ANOVA) for repeated
measurements was used to assess changes over time within,
as well as between, groups and one-way ANOVA was
performed to compare raw data between groups. Post hoc
analysis to allow for multiple comparisons was performed
using the Bonferroni±Dunn correction. Student's t-test was
used to make single comparisons of cuff pressure, volume,
and concentration of nitrous oxide. Proportional data were
evaluated using the chi-square test. A P-value of <0.05 was
considered to be statistically signi®cant.
Results
Gender, age, weight, and height of the patients were
comparable among groups (Table 1). There was no
273
Karasawa et al.
signi®cant difference among groups in either initial cuff
pressure or volume injected into the cuffs (Table 2).
Changes in cuff pressure in group 12H are shown in
Figure 1. In some patients the studies were ®nished before
12 h because surgery was completed. The cuff pressure
exceeded 22 mm Hg in some patients but there was no
signi®cant difference among groups. Volume in the cuff
increased signi®cantly in groups 2H, 4H, 8H, and 12H
(Table 2).
Gas concentrations and corresponding volume
Gas concentrations in the cuff and pilot balloon estimated
using Equation 1 are shown in Table 2. Nitrous oxide
Fig 2 Changes in the gas concentration in the cuff and pilot balloon of the BrandtÔ system (open and grey column in left panel, respectively) and the
corresponding volume (right panel) at 0.5, 1, 2, 4, 8, and 12 h (group 0.5H, 1H, 2H, 4H, 8H, and 12H, respectively); n=10 for each. Note that gas
concentrations in cuffs were estimated using Equation 1 and that the statistical comparisons of gas concentrations between groups are presented in
Table 2. *P<0.05 vs initial values (air). ²P<0.05 vs values in the pilot balloon of the same group. ³P<0.05 between corresponding volume injected and
aspirated, calculated using Equations 2 and 3, respectively.
274
Nitrous oxide concentration in the BrandtÔ tube cuff
concentration in the cuff increased with time (P<0.001),
becoming more than 40% after 4 h of anaesthesia; that in the
pilot balloon signi®cantly increased with time (P<0.001),
becoming approximately 2% (Table 2, Fig. 2). Nitrous
oxide volume in the pilot balloon and cuff increased
signi®cantly (2.6 (0.8) ml for 4 h, Fig. 2). Nitrogen and
oxygen concentration in the cuff decreased time-dependently during anaesthesia (P<0.001); however, corresponding volumes did not change signi®cantly (Fig. 2). Carbon
dioxide concentration in the cuff increased with time (Fig.
2).
separated cuff, the separated cuff in a glass tube, the HiContourÔ tracheal tube, and the Hi-ContourÔ tracheal tube
in a glass tube, at 15 mm Hg (points of R, R¢, B, C, C¢, I, and
I¢ in Fig. 3) were 0.34 (0.10), 0.28 (0.03), 0.22 (0.02), 0.11
(0.01), 0.03 (0.005), 0.10 (0.015), and 0.05 (0.004) ml (mm
Hg)±1, respectively. Although the ratio of the BrandtÔ to
the Hi-ContourÔ tracheal tube compliance was approximately 3.4, it became 5.7 when the tracheal tubes were
placed in a glass tube.
Compliance of the cuff and pilot balloon
Cuff pressure in the BrandtÔ tracheal tube was assessed
during nitrous oxide anaesthesia. Cuff pressure was stable
for more than 10 h, whereas previous studies9 10 were for
less than 3 h. During the ®rst 4 h, cuff pressure gradually
increased; the increase in cuff volume was 2.2 ml for 4 h of
anaesthesia. We abandoned assessment of the increase in
cuff volume of standard tracheal tubes for the control group
in this study because the cuff pressure of the standard tubes
increased so quickly that it would cause tracheal damage. In
our previous reports,3 8 the rate of increase of cuff volume
was dependent on tube design and ranged from 0.7 to 2.8 ml
h±1. Therefore, the BrandtÔ system limits the increase in
cuff volume more effectively (1.5±5 times) than other
tracheal tubes.
In this study we measured gas concentrations in both cuff
and pilot balloon, separately. Nitrous oxide concentration in
the cuff increased during anaesthesia and became greater
than 40% after 4 h. This value is similar to the equilibrating
concentration in standard tracheal tubes in our previous
study (40±50%).3 In contrast, nitrous oxide concentration in
the pilot balloon was only 2% in the present study. This
large concentration gradient between the cuff and pilot
balloon might be a result of a narrow connecting tube and
slow transfer between the cuff and pilot balloon.
Consequently, nitrous oxide concentration in the cuff
approached the equilibrating concentration, which would
limit nitrous oxide diffusion into the cuff.
Because the BrandtÔ system consists of a cuff and
balloon in series, total compliance of the system (0.34 ml
(mm Hg)±1) is approximately equal to the sum of the
compliance of the cuff (0.11 ml (min Hg)±1) and compliance
of the balloon (0.22 ml (mm Hg)±1). The total compliance is
3.3 times greater than that of the cuff only. Because the
When the tracheal tube was placed in a glass tube, the
volume±pressure relationship of both the total BrandtÔ
system and the separated cuff moved to the left (Fig. 3).
Compliances of the BrandtÔ tracheal tube, the BrandtÔ
tracheal tube in a glass tube, the separated pilot balloon, the
Fig 3 Volume±pressure relationships of the BrandtÔ tracheal tube, the
separated pilot balloon and cuff, and the Hi-ContourÔ tracheal tube.
When the tracheal cuff was placed in a glass tube, the volume±pressure
relationships of the intact tube cuff and the separated cuff in the
BrandtÔ tube shifted to the left. The relationships of the Hi-ContourÔ
tracheal tube also moved to the left (closed square), which is almost
same as that of cuff only (closed triangle). The R, R¢, B, I, C, I¢, and C¢
markers denote intersection points of the relationship and the dotted line
that expresses pressure indicates 15 mm Hg. Compliance was calculated
as the reciprocal of the gradient of the relationship at each point.
Discussion
Table 3 Gas concentrations (%) in air, gas mixture used in this study, and gases aspirated from cuffs or pilot balloons of the BrandtÔ system to measure
dead volume of the cuff and pilot balloon. Data are expressed as number of samples or mean (SD). *The ratio of fresh gas ¯ow of air and oxygen used in this
study was 6:1
Air
n
Nitrous oxide
Nitrogen
Oxygen
Carbon dioxide
11
0.0
78.1
20.9
0.2
(0.1)
(0.1)
(0.1)
(0.7)
Gas mixture*
In cuffs
In pilot balloons
11
0.1
8.1
91.7
0.0
5
0.1
10.4
89.5
0.0
5
0.1
11.4
88.4
0.0
(0.0)
(0.1)
(0.1)
(0.0)
275
(0.0)
(0.3)
(0.3)
(0.0)
(0.1)
(0.2)
(0.2)
(0.0)
Karasawa et al.
compliance of the balloon is not affected by restricting the
tracheal tube cuff, the ratio of total compliance to cuff
compliance in a glass tube becomes much higher (8.2
times), which might contribute, in part, to the small changes
in cuff pressure with nitrous oxide. The compliance of the
BrandtÔ tube cuff was 5.7 times higher than that of the HiContourÔ tracheal tube when assessed in a glass tube.
Therefore, the compliant balloon of the BrandtÔ system
also appears to contribute to a stable-cuff pressure.
In this study, we assessed the volume change of each gas
in the cuff and pilot balloon. The concentration of each gas
changes because of the dilution effect from the increased
amount of nitrous oxide. Although nitrogen and oxygen
concentrations decreased signi®cantly during anaesthesia,
the volume changes were not signi®cant (Fig. 2). On the
other hand, carbon dioxide concentration in the cuff and
pilot signi®cantly balloon increased, and the volume
increased signi®cantly.
Tracheal cuff pressure should be maintained below 22
mm Hg and never exceed 37 mm Hg so that ischaemic
mucosal damage can be avoided. We assessed the number of
patients whose cuff pressure exceeded 22 mm Hg. By
controlling cuff pressure, sore throat from tracheal intubation can be reduced by half.3 5 12±15 Taken together, the
BrandtÔ tracheal tube is effective during anaesthesia with
nitrous oxide, even with prolonged anaesthesia.
The BrandtÔ system preserves stable-cuff pressure
because of its highly compliant cuff/balloon rather than
because an increase in the cuff volume is emitted. The
nitrous oxide concentration gradient between the cuff and
pilot balloon is probably another factor that restrains cuff
pressure in the BrandtÔ tracheal tube because high
concentrations of nitrous oxide in the cuff will reduce
nitrous oxide diffusion from the airway gases.
was aspirated immediately after ®lling the cuff three times.
The nitrogen concentration (Table 3) was measured using
mass-spectrometry (AMIS 2000) and the dead volume
(Vdead) in the cuff (Vdead[cuff]) and pilot balloon (Vdead[pb])
were calculated using the following formula:
Vinj3(Casp±Cinj)/(Cair±Casp)
where Vinj is the volume (ml) of gas for in¯ating, and Cinj,
Casp, or Cair denote gas concentration (i.e. nitrogen) of the
injected or aspirated gases, or air, respectively.
The nitrogen concentration in the gas aspirated from the
cuff and pilot balloon are shown in the Table 3. The
estimated dead volume of the cuff was 0.2 (0.03) ml; that of
the pilot balloon was 1.3 (0.1) ml.
References
Appendix
Measurement of dead volume
Because nitrogen barely permeates polyvinyl chloride,
nitrogen was used as a dilution indicator to measure the
dead volume. A gas mixture of air and oxygen was obtained
from the common outlet of the anaesthetic machines (Excel
210, Ohmeda, Madison, WI); the ratio of fresh gas ¯ow of
air and oxygen used in this in vitro study was 6:1. Using
quadropole mass-spectrometry (AMIS 2000), actual concentrations of nitrogen as well as nitrous oxide, oxygen, and
carbon dioxide in the gas mixtures and air were measured
(Table 3).
The connecting tube between the cuff and pilot balloon of
the BrandtÔ system was cut approximately 2 cm from the
pilot balloon. The cuff or pilot balloon (n=5 for each) was
then de¯ated as much as possible using a plastic syringe and
subsequently in¯ated with 7 or 25 ml of the gas mixture,
respectively. The gas mixture in the cuff and pilot balloon
276
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