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

Accepted for publication: March 18, 2002


    Abstract
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Appendix
 References
 
Background. The BrandtTM 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 BrandtTM system.

Methods. The pressure in an air-filled cuff of the BrandtTM system (Mallinckrodt BrandtTM 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 first 4 h of anaesthesia. The carbon dioxide volume increased slightly, and nitrogen and oxygen did not change significantly. The compliance of the BrandtTM tube cuff was six times greater than that of a standard tube cuff (Mallinckrodt Hi-ContourTM tracheal tube).

Conclusions. The BrandtTM 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 influx.

Br J Anaesth 2002; 89: 271–6

Keywords: anaesthetics gases, nitrous oxide; equipment, cuffs tracheal; equipment, tubes tracheal


    Introduction
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Appendix
 References
 
Nitrous oxide easily permeates polyvinyl chloride, the material of tracheal tube cuffs, so that cuff pressure increases during anaesthesia with nitrous oxide.13 To avoid this, the cuff should be repeatedly deflated 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.48 Among them, the BrandtTM system,9 which has a large pilot balloon that facilitates efflux 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 BrandtTM 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 balloon of the system is thin, we hypothesized that the high compliance of the BrandtTM system contributes to the stable-cuff pressure.


    Methods
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Appendix
 References
 
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 BrandtTM 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 inflated with the lowest volume of air that would not leak when the intra-airway pressure was 18 cm H2O. The volume used to fill the cuff and the initial sealing pressure was recorded. Anaesthesia was maintained with 67% nitrous oxide and 33% oxygen, supplemented with isoflurane or sevoflurane, 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 UltimaTM, Datex, Helsinki, Finland). A humidifier was used, but use of a nasogastric tube was avoided.

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 first 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- spectrometry (AMIS 2000, INNVISION A/S, Odense, Denmark), which was calibrated with standard gases.

Data analysis
Correction of gas concentrations
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:

(CaspxVaspCasp[pb]xVdead[pb])/(VaspVdead[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])xCair(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])xCasp[cuff]        +(Vasp[pb]+Vdead[pb])xCasp[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 2-Equation 3.

Measurement of compliance in vitro
To assess the volume–pressure relationship of the BrandtTM system, the pilot balloon and the cuff of the Hi-Contour BrandtTM and the Hi-ContourTM (n=5 for each) tracheal tubes were inflated with air, 2 ml at a time, using a syringe. Then the connection tubes of the BrandtTM tracheal tubes (n=5) were cut 2 cm from the pilot balloon. The pilot balloon and the cuff were inflated separately with air, 0.5 or 1 ml at a time. The inflated volume and the intra-cuff pressure were recorded. The Hi-ContourTM tracheal tube is a standard tracheal tube and has the same type and volume of cuff as the Hi-Contour BrandtTM tracheal tube. In addition, the tracheal tube (n=5) was placed in an 18.2-mm diameter glass tube (approximately the same cross-sectional diameter as an adult female trachea), and the intact BrandtTM system or cuff only was inflated with air to measure the volume–pressure relationship in a condition similar to the clinical situation. Compliance 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
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 significant.


    Results
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Appendix
 References
 
Gender, age, weight, and height of the patients were comparable among groups (Table 1). There was no significant 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 finished before 12 h because surgery was completed. The cuff pressure exceeded 22 mm Hg in some patients but there was no significant difference among groups. Volume in the cuff increased significantly in groups 2H, 4H, 8H, and 12H (Table 2).


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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
 

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Table 2 Cuff pressure, volume, and gas concentrations in the cuff and pilot balloon of the BrandtTM 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 significance. *P<0.01 vs volume injected. {dagger}P<0.01 vs values in the 0.5H group. {ddagger}P<0.01 vs values in the 1H group. P<0.01 vs values in the 2H group
 


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Fig 1 Changes in the air-filled cuff pressure of the BrandtTM tracheal tube (group 12H). During nitrous oxide anaesthesia, cuff pressure increased slightly; the closed circle denotes a significant increase in cuff pressure (P<0.05 vs initial values). When anaesthesia was finished before the completion of the study, the number of patients included in the statistical analysis is shown by the marker of each point.

 
Gas concentrations and corresponding volume
Gas concentrations in the cuff and pilot balloon estimated using Equation 1 are shown in Table 2. Nitrous oxide concentration in the cuff increased with time (P<0.001), becoming more than 40% after 4 h of anaesthesia; that in the pilot balloon significantly increased with time (P<0.001), becoming approximately 2% (Table 2, Fig. 2). Nitrous oxide volume in the pilot balloon and cuff increased significantly (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 significantly (Fig. 2). Carbon dioxide concentration in the cuff increased with time (Fig. 2).



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Fig 2 Changes in the gas concentration in the cuff and pilot balloon of the BrandtTM 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). {dagger}P<0.05 vs values in the pilot balloon of the same group. {ddagger}P<0.05 between corresponding volume injected and aspirated, calculated using Equations 2 and 3, respectively.

 
Compliance of the cuff and pilot balloon
When the tracheal tube was placed in a glass tube, the volume–pressure relationship of both the total BrandtTM system and the separated cuff moved to the left (Fig. 3). Compliances of the BrandtTM tracheal tube, the BrandtTM tracheal tube in a glass tube, the separated pilot balloon, the separated cuff, the separated cuff in a glass tube, the Hi-ContourTM tracheal tube, and the Hi-ContourTM 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 BrandtTM to the Hi-ContourTM tracheal tube compliance was approximately 3.4, it became 5.7 when the tracheal tubes were placed in a glass tube.



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Fig 3 Volume–pressure relationships of the BrandtTM tracheal tube, the separated pilot balloon and cuff, and the Hi-ContourTM 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 BrandtTM tube shifted to the left. The relationships of the Hi-ContourTM 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
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Appendix
 References
 
Cuff pressure in the BrandtTM 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 first 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 BrandtTM 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 BrandtTM 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 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 BrandtTM tube cuff was 5.7 times higher than that of the Hi-ContourTM tracheal tube when assessed in a glass tube. Therefore, the compliant balloon of the BrandtTM 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 significantly during anaesthesia, the volume changes were not significant (Fig. 2). On the other hand, carbon dioxide concentration in the cuff and pilot significantly balloon increased, and the volume increased significantly.

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 1215 Taken together, the BrandtTM tracheal tube is effective during anaesthesia with nitrous oxide, even with prolonged anaesthesia.

The BrandtTM 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 BrandtTM tracheal tube because high concentrations of nitrous oxide in the cuff will reduce nitrous oxide diffusion from the airway gases.


    Appendix
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Appendix
 References
 
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 flow 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).


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Table 3 Gas concentrations (%) in air, gas mixture used in this study, and gases aspirated from cuffs or pilot balloons of the BrandtTM 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 flow of air and oxygen used in this study was 6:1
 
The connecting tube between the cuff and pilot balloon of the BrandtTM system was cut approximately 2 cm from the pilot balloon. The cuff or pilot balloon (n=5 for each) was then deflated as much as possible using a plastic syringe and subsequently inflated with 7 or 25 ml of the gas mixture, respectively. The gas mixture in the cuff and pilot balloon was aspirated immediately after filling 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:

Vinjx(CaspCinj)/(CairCasp)

where Vinj is the volume (ml) of gas for inflating, 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
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Appendix
 References
 
1 Stanley TH, Kawamura R, Graves C. Effects of nitrous oxide on volume and pressure of endotracheal tube cuffs. Anesthesiology 1974; 41: 256–62[ISI][Medline]

2 Al-Shaikh B, Jones M, Baldwin F. Evaluation of pressure changes in a new design tracheal tube cuff, the Portex Soft Seal, during nitrous oxide anaesthesia. Br J Anaesth 1999; 83: 805–06[Abstract/Free Full Text]

3 Karasawa F, Ohshima T, Takamatsu I, et al. The effect on intracuff pressure of various nitrous oxide concentrations used for inflating an endotracheal tube cuff. Anesth Analg 2000; 91: 708–13[Abstract/Free Full Text]

4 Kim JM. The tracheal tube cuff pressure stabilizer and its clinical evaluation. Anesth Analg 1980; 59: 291–96[ISI][Medline]

5 Mandoe H, Nikolajsen L, Lintrup U, et al. Sore throat after endotracheal intubation. Anesth Analg 1992; 74: 897–900[Abstract]

6 Payne KA, Miller DM. The Miller tracheal cuff pressure control valve. Anaesthesia 1993; 48: 324–27[ISI][Medline]

7 Umezono Y, Fujita A, Toi T, Sakio H. Usefulness of tracheal tubes with N2O gas-barrier cuff. MASUI-Jpn J Anesthesiol 1999; 48: 1250–52

8 Karasawa F, Mori T, Okuda T, Satoh T. Profile Soft-Seal Cuff, a new endotracheal tube, effectively inhibits an increase in the cuff pressure through high compliance rather than low diffusion of nitrous oxide. Anesth Analg 2001; 92: 140–44[Abstract/Free Full Text]

9 Brandt L, Pokar H. The rediffusion system: limitation of nitrous oxide-induced increase of the pressure of endotracheal tube cuffs. Anaesthetist 1983; 32: 459–64[ISI][Medline]

10 Fill DM, Dosch MP, Bruni MR. Rediffusion of nitrous oxide prevents increases in endotracheal tube cuff pressure. AANA J 1994; 62: 77–81[Medline]

11 Seegobin RD, Hasselt GL. Endotracheal cuff pressure and tracheal mucosal blood flow: endoscopic study of effects of four large volume cuffs. Br Med J 1984; 288: 965–68[ISI][Medline]

12 Capan LM, Bruce DL, Patel KP, Turndorf H. Succinylcholine-induced postoperative sore throat. Anesthesiology 1983; 59: 202–6[ISI][Medline]

13 Monroe M, Gravenstein N, Saga-Rumley S. Postoperative sore throat: effect of oropharyngeal airway in orotracheally intubated patients. Anesth Analg 1990; 70: 512–26[Abstract]

14 Hakim ME. Beclomethasone prevents postoperative sore throat. Acta Anaesthesiol Scand 1993; 37: 250–52[ISI][Medline]

15 Loeser EA, Kaminsky A, Diaz A, et al. The influence of endotracheal tube cuff design and cuff lubricant on postoperative sore throat. Anesthesiology 1983; 58: 376–79[ISI][Medline]





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