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BJA Advance Access originally published online on December 25, 2008
British Journal of Anaesthesia 2009 102(2):273-278; doi:10.1093/bja/aen355
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© The Board of Management and Trustees of the British Journal of Anaesthesia 2008. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

Rapid pressure compensation by automated cuff pressure controllers worsens sealing in tracheal tubes

M. Weiss1,*,{dagger}, C. Doell2,{dagger}, N. Koepfer1,{dagger}, C. Madjdpour1,{dagger}, K. Woitzek1,{dagger} and V. Bernet2,{dagger}

1 Department of Anaesthesia
2 Department of Intensive Care and Neonatology, University Children's Hospital, Steinwiesstrasse 75, 8032 Zurich, Switzerland

* Corresponding author. E-mail: markus.weiss{at}kispi.uzh.ch

Accepted for publication October 27, 2008.


   Abstract
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 Abstract
Introduction
 Methods
 Results
 Discussion
 Supplementary material
 Funding
 References
 
Background: Cyclic redistribution of air within the cuff during respiratory pressure changes creates a self-sealing mechanism which allows tracheal sealing, despite tracheal airway pressure being above baseline cuff inflation pressure. The aim of the present study was to investigate the effect of continuous automated cuff pressure regulation on tracheal sealing during cyclic respiratory pressure changes.

Methods: In vitro tracheal sealing was studied in four different high volume–low pressure (HVLP) tracheal tube cuffs size internal diameter 8.0 and 5.0 mm in combination with a conventional pressure manometer and two different automated pressure controllers (VBM Cuff Controller; Cuff Pressure Control TracoeTM). Experiments were performed at 10, 15, 20, and 25 cm H2O cuff pressure during intermittent positive pressure ventilation with peak inspiratory pressures of 20 and 25 cm H2O. Air leakage was assessed spirometrically. Experiments were performed four times with each tube brand and size with two exemplars of each of the three cuff pressure controllers.

Results: Owing to immediate cuff pressure correction, tracheal sealing at cuff pressure below inspiratory pressure was reduced in most of the tracheal tube cuffs, except in those with reduced sealing characteristics when using the Pressure Control TracoeTM compared with the conventional pressure manometer and the VBM Cuff Controller. Tracheal sealing with the Pressure Control TracoeTM comparable with the other two devices was only achieved at cuff pressures of 20 and 25 cm H2O.

Conclusions: Automated cuff pressure controllers with rapid pressure correction interfere with the self-sealing mechanism of high sealing HVLP tube cuffs and reduce their improved sealing characteristics.

Keywords: airway; complications, aspiration; ventilation


   Introduction
Top
 Abstract
 Introduction
Methods
 Results
 Discussion
 Supplementary material
 Funding
 References
 
High volume–low pressure (HVLP) tube cuffs seal the trachea at baseline cuff pressures lower than peak airway pressure by the so-called self-sealing mechanism.12 Tracheal airway pressure thereby produces a retrograde compression in the distal part of the cuff and moves air within the cuff proximally towards the upper end. This results in tracheal sealing.3 4 The cyclic redistribution of air within the cuff creates a self-sealing mechanism, which allows tracheal occlusion by the cuff, despite an increase in distal tracheal airway pressure above baseline cuff inflation pressure.

In the past, several cuff pressure regulators have been introduced in clinical practice in order to limit cuff pressures and to maintain cuff pressure by continuously inflating and deflating.5–12 This study aimed to investigate the effect of continuous cuff pressure regulation by two different modern automated cuff pressure controllers on tracheal self-sealing in different HVLP tracheal tube cuffs.


   Methods
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 Abstract
 Introduction
 Methods
Results
 Discussion
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In an in vitro laboratory model, we investigated the sealing quality of HVLP tracheal tube cuffs in combination with a manual cuff pressure controller (Cuff pressure manometer, Microcuff GmbH, Weinheim, Germany) and two automated cuff pressure controllers (VBM Cuff Controller, VBM Medizintechnik GmbH, Sulz a.N., Germany, and Cuff Pressure Control, TracoeTM, TRACOE medical GmbH, Frankfurt, Germany) (Fig. 1). All devices tested were new and represented the latest version from each manufacturer. Before measurements, the devices were tested and calibrated if necessary according to the manufacturers’ instructions for use.


Figure 1
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  		Fig 1 Cuff pressure controllers tested: (A) Cuff Pressure Manometer, Microcuff GmbH, Weinheim, Germany; (B) VBM Pressure Controller, VBM Medizintechnik GmbH, Sulz a.N., Germany; (C) TracoeTM Pressure Controller, TRACOE medical GmbH, Frankfurt, Germany.

 
A mechanical lung (Testlung, Carbamed, Zurich, Switzerland—Compliance 22 ml cm H2O–1) connected to a model trachea made from clear, rigid polyvinylchloride (PVC) [20 mm, respectively, 12 mm internal diameter (ID)] was used to simulate changes in inspiratory pressures. ID 8.0 and 5.0 mm tracheal tubes with a HVLP cuff from different manufacturers were used (Table 1). The deflated, unlubricated tracheal tube cuffs were completely inserted into the model trachea and connected to the ventilator. The cuff inflation line was connected to one of the three cuff pressure controller devices tested. Inspiratory and expiratory tidal volumes were measured with a spirometer (Spirometer, AS5 Monitor, Datex Ohmeda, Helsinki, Finland) interposed between the ventilator and the tracheal tube. Pressure-controlled ventilation was provided by an anaesthesia respirator (ADU, Datex Ohmeda). Respirator settings were: fresh gas flow (air) 6 litre min–1; PEEP 5 cm H2O; ventilatory frequency 10 bpm; I:E ratio 1:2; inspiratory pressure 15 and 20 cm H2O [peak inspiratory pressure (PIP) 20 and 25 cm H2O]. With the ventilator bellows completely filled with air, experiments were started using cuff pressures of 10, 15, 20, and 25 cm H2O, respectively.


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  		Table 1 Investigated tracheal tubes with HVLP cuffs with ID of 8.0 and 5.0 mm. PU, polyurethane; PVC, polyvinyl chloride

 
Minimal and maximal cuff pressures, as indicated by the corresponding device, and inspiratory and expiratory volumes were measured. Ratio of expiratory to inspiratory tidal volumes (VtE/VtI ratio) was calculated.

Experiments were performed four times using four new tracheal tubes with two exemplars of each of the three cuff pressure controllers at room temperature of 20–22°C.

Measured VtE/VtI ratios and maximal and minimal cuff pressures were compared using two-tailed Student's t-test within the two identical devices, the two different PIP levels, and the tube sizes from the same manufacturer. Similarly, data were compared between the conventional cuff pressure manometer and the VBM and the TracoeTM pressure controllers and between the Microcuff tracheal tube and the three other tracheal tube brands for each size. Data are presented as mean (SD).


   Results
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 Abstract
 Introduction
 Methods
 Results
Discussion
 Supplementary material
 Funding
 References
 
A total of 1526 measurements were made. There were no statistically significant differences between two similar pressure control devices or between experiments performed with 20 and 25 cm H2O PIP, except that maximum cuff pressures recorded with the cuff pressure manometer were higher in some of the ID 8.0 mm tracheal tubes. With the conventional cuff pressure, manometer sufficient tracheal sealing (<5% air leakage; approximately ≤20 ml per tidal volume) at all cuff pressures and both PIPs tested was only obtained in the Microcuff tracheal tubes ID 8.0 and 5.0 mm. In the other three tracheal tube brands, tracheal sealing was significantly reduced, whereas two out of three ID 5.0 mm tube cuffs demonstrated significantly better values than their corresponding ID 8.0 mm sizes (Table 2).


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  		Table 2 Summarized air leakage, minimum and maximum cuff pressures measured for the three cuff pressure controllers and for the ID 8.0 and 5.0 mm tracheal tubes. Data are the mean values obtained from all measurements (cuff pressures of 10, 15, 20, and 25 cm H2O and PIPs of 20 and 25 cmH2O). Cuff pressure controllers compared with cuff pressure manometer: ****P<0.0001, ***P<0.001, **P<0.01, *P<0.05. Tracheal tube sizes ID 5.0 mm compared with ID 8.0 mm: ++++P<0.0001, +++P<0.001, ++P<0.01, +P<0.05. Tracheal tube brands compared with similar sized Microcuff tracheal tubes: ####P<0.0001, ###P<0.001, ##P<0.01, #P<0.05. PIPs 20 vs 25 cm H2O: {int}{int}{int}P<0.001, {int}P<0.05

 
Tracheal sealing obtained with the VBM pressure controller was similar to that obtained with the cuff pressure manometer at all cuff pressure levels in most of the tubes; however, tracheal sealing was reduced with the TracoeTM Pressure Controller. This was seen in most of the tracheal tubes tested (Table 2, Figs 2 and 3) except in the Portex tracheal tubes, demonstrating the lowest sealing qualities of all tubes. The TracoeTM Pressure Controller achieved tracheal sealing comparable with that of the cuff pressure manometer only at cuff pressures of 20 and 25 cm H2O (Figs 2 and 3). The VBM Pressure Controller achieved even better sealing than the cuff manometer in two high quality sealing tube cuffs. However, this device showed a similarly poor performance to the TracoeTM Pressure Controller in the 5.0 mm Portex tracheal tubes (Table 2).


Figure 2
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  		Fig 2 Mean ratio (%) of expiratory to inspiratory tidal volumes recorded with each of the three cuff pressure controllers and each of the four different ID 8.0 mm tracheal tube brands tested at cuff pressures of 10, 15, 20, and 25 cm H2O and at peak inflation pressure of 20 and 25 cm H2O (n=16 measurements per device, tracheal tube brand, cuff pressure and inspiratory peak pressure).

 


Figure 3
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  		Fig 3 Mean ratio (%) of expiratory to inspiratory tidal volumes recorded with each of the three cuff pressure controllers and each of the four different ID 5.0 mm tracheal tube brands tested at cuff pressures of 10, 15, 20, and 25 cm H2O and at peak inflation pressure of 20 and 25 cm H2O (n=16 measurements per device, tracheal tube brand, cuff pressure and inspiratory peak pressure).

 
Cyclic cuff pressure changes noted from the devices corresponded well to baseline cuff pressures and set PIPs in the conventional cuff manometer and the VBM device (Supplementary material, Tables 1 and 2). In all tracheal tubes tested, the TracoeTM pressure controller demonstrated minimal cuff pressures significantly lower than the set cuff pressure. Similarly, maximal cuff pressures recorded with the TracoeTM pressure controller were significantly lower than the other two devices but only in the ID 8.0 sized tracheal tubes. Notably, cuff pressure regulation with the TracoeTM pressure controller was accompanied by continuous audible deflating and inflating noises, particularly at cuff inflation pressure of 10–20 cm H2O.


   Discussion
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
Supplementary material
 Funding
 References
 
Maintaining an appropriate cuff pressure in mechanically ventilated patients is important in order to avoid cuff hyperinflation as a consequence of manual cuff inflation or nitrous oxide diffusion and to guarantee constant proper sealing of the trachea. Automated cuff pressure controllers have been introduced to overcome these risks and to keep the cuff constantly inflated. The main finding of our study clearly demonstrates that a rapid compensating pressure controller worsens tracheal sealing in HVLP tube cuffs with improved sealing qualities, but not in those with reduced sealing characteristics, independent from tube size and tube brand.

Inadequate sealing leading to leakage of contaminated secretions pooled above the tracheal tube cuff and then to ventilator-associated pneumonia (VAP) is of increasing interest.13 14 The routine management of cuff inflation in the intensive care unit consists of a periodic manual check of cuff pressure. Connection/disconnection of a conventional cuff manometer to/from the cuff inflation line and manipulation (increasing/reducing) of the cuff pressure leads to pressure drops.15 In addition, sudden changes in tracheal diameter or gas diffusion across the cuff membrane down the pressure gradient prevent an unchanged cuff pressure and an equal cuff expansion. In contrast to periodically adjusting the cuff pressure in ventilated intensive care patients, automated cuff controllers provide a more constant cuff pressure.16 To date only one study was able to demonstrate that intermittent cuff pressures of <20 cm H2O are a risk factor for VAP.15

As demonstrated by our results, sealing characteristics between tube brands tested differed considerably (Table 2) which is consistent with earlier published investigations.2 17 As shown by Young and colleagues,18 the reduced sealing characteristics of some of these tubes are caused by the formation of folds and channels within the cuff, when they are inflated in the tracheal lumen. Therefore, beside oropharyngeal contamination, head-of-the-bed elevation, subglottic continuous suctioning of secretions, and continuous cuff pressure control, in the past 10 yr tracheal tube cuffs with improved sealing characteristics, avoiding longitudinal channels and folds, have been developed in order to reduce VAP.17 19–22 In particular, the new ultrathin polyurethane cuffs not only reduce micro-aspiration,21 22 but also allow tracheal sealing at cuff pressure much lower than inspiratory pressure by their self-inflating mechanism2–4 as confirmed by our investigation. Lower cuff pressures are very desirable in long-term ventilated patients in order to prevent cuff pressure-related injury to the trachea, including tracheomalacia and tracheal dilatation. However, to date, there are no data, whether the cyclic decompression—associated with the self-inflation mechanism of high volume low pressure tracheal tube cuffs—has itself an impact on tracheal sealing, respectively on micro-aspiration of subglottic pooled secretions past the tube cuff.

On the basis of our in vitro findings, automatic cuff pressure regulators may interfere with the self-sealing mechanism of HVLP tube cuffs, as long as the set cuff pressures are lower than PIPs. This can be explained by the rapid compensations or even overcompensation (lower than set cuff pressure) of any elevated cuff pressures, such as in the TracoeTM device. The implication of our findings is that in automated cuff pressure controllers, the cuff pressure set should be similar to PIP to avoid cyclic up- and down-regulation by these devices. An ideally designed automated cuff pressure controller should immediately stabilize any acute cuff pressure drops (sudden widening of the trachea before coughing) or chronic fall in cuff pressure (out diffusion of air from the cuff), whereas elevated cuff pressures by respiratory pressures or coughing should be corrected only by slow decompression.

However, two limitations of this study have to be mentioned. First, the in vitro testing of tracheal tube cuffs was performed in circular tracheas, which are different from the human d-shaped trachea and may affect tracheal sealing. Secondly, we did not lubricate the cuffs, mimicking the wet mucosal layer, in order not to eliminate small differences, which may become important over a longer time, since sealing by tracheal mucous is not a constant factor.

In conclusion, automated cuff pressure controllers with rapid correction of cuff pressure increases reduce the improved sealing characteristics of HLVP tube cuffs at cuff pressures lower than airway pressures. Development of pressure controllers with rapid correction of cuff pressure drops and delayed release of increased pressures is needed. Until then, cuff pressure should be set closely to PIP when using automated cuff pressure controllers.


   Supplementary material
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Supplementary material
Funding
 References
 
Supplementary material is available at British Journal of Anaesthesia online.


   Funding
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Supplementary material
 Funding
References
 
The study was supported by departmental resources.


   Footnotes
 
{dagger} Declaration of interest. The tracheal tubes and the cuff regulators studied were ordered from local distributors. No financial support was obtained from the manufacturers for the present study. No agreements or financial benefits arise from these co-operations. There are no financial or non-financial competing interests in the accomplishment of this study. Back


   References
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Supplementary material
 Funding
 References
 
1 Dullenkopf A, Gerber AC, Weiss M. Fit and seal characteristics of a new paediatric tracheal tube with high volume–low pressure polyurethane cuff. Acta Anaesthesiol Scand (2005) 49:232–7.[CrossRef][Web of Science][Medline]

2 Dullenkopf A, Schmitz A, Frei M, Gerber AC, Weiss M. Air leakage around endotracheal tube cuffs. Eur J Anaesthesiol (2004) 21:448–53.[CrossRef][Web of Science][Medline]

3 Carroll RG, McGinnis GE, Grenvik A. Performance characteristics of tracheal cuffs. Int Anesthesiol Clin (1974) 12:111–41.[Medline]

4 Guyton D, Banner MJ, Kirby RR. High-volume, low-pressure cuffs. Are they always low pressure? Chest (1991) 100:1076–81.[Abstract/Free Full Text]

5 Abdelatti MO. A cuff pressure controller for tracheal tubes and laryngeal mask airways. Anaesthesia (1999) 54:981–6.[CrossRef][Web of Science][Medline]

6 Duguet A, D'Amico L, Biondi G, et al. Control of tracheal cuff pressure: a pilot study using a pneumatic device. Intensive Care Med (2007) 33:128–32.[CrossRef][Web of Science][Medline]

7 Farre R, Rotger M, Ferre M, Torres A, Navajas D. Automatic regulation of the cuff pressure in endotracheally-intubated patients. Eur Respir J (2002) 20:1010–3.[Abstract/Free Full Text]

8 Kassam M, Johnston KW, Cobbold RS. An automatic, multi-function pressure cuff control unit. Med Prog Technol (1977) 5:157–60.[Web of Science][Medline]

9 Kunitz O, Jansen R, Ohnsorge E, et al. Cuff pressure monitoring and regulation in adults. Anaesthesist (2004) 53:334–40.[CrossRef][Web of Science][Medline]

10 Miller DM. A pressure regulator for the cuff of a tracheal tube. Anaesthesia (1992) 47:594–6.[Web of Science][Medline]

11 Morris JV, Latto IP. An electropneumatic instrument for measuring and controlling the pressures in the cuffs of tracheal tubes: ‘the Cardiff Cuff Controller. J Med Eng Technol (1985) 9:229–30.[Web of Science][Medline]

12 Willis BA, Latto IP, Dyson A. Tracheal tube cuff pressure. Clinical use of the Cardiff Cuff Controller. Anaesthesia (1988) 43:312–4.[Web of Science][Medline]

13 Young PJ, Ridley SA. Ventilator-associated pneumonia. Diagnosis, pathogenesis and prevention. Anaesthesia (1999) 54:1183–97.[CrossRef][Web of Science][Medline]

14 Kollef MH. The prevention of ventilator-associated pneumonia. N Engl J Med (1999) 340:627–34.[Free Full Text]

15 Estes RJ, Meduri GU. The pathogenesis of ventilator-associated pneumonia: I. Mechanisms of bacterial transcolonization and airway inoculation. Intensive Care Med (1995) 21:365–83.[CrossRef][Web of Science][Medline]

16 Rello J, Sonora R, Jubert P, et al. Pneumonia in intubated patients: role of respiratory airway care. Am J Respir Crit Care Med (1996) 154:111–5.[Abstract]

17 Dullenkopf A, Gerber AC, Weiss M. Fluid leakage past tracheal tube cuffs: evaluation of the new Microcuff endotracheal tube. Intensive Care Med (2003) 29:1849–53.[CrossRef][Web of Science][Medline]

18 Young PJ, Rollinson M, Downward G, Henderson S. Leakage of fluid past the tracheal tube cuff in a bench top model. Br J Anaesth (1997) 78:557–62.[Abstract/Free Full Text]

19 Young PJ, Ridley SA, Downward G. Evaluation of a new design of tracheal tube cuff to prevent leakage of fluids to the lung. Br J Anaesth (1998) 80:796–9.[Abstract/Free Full Text]

20 Young PJ, Blunt MC. Improving the shape and compliance characteristics of a high-volume, low-pressure cuff improves tracheal seal. Br J Anaesth (1999) 83:887–9.[Abstract/Free Full Text]

21 Lorente L, Lecuona M, Jimenez A, Mora ML, Sierra A. Influence of an endotracheal tube with polyurethane cuff and subglottic secretion drainage on pneumonia. Am J Respir Crit Care Med (2007) 176:1079–83.[Abstract/Free Full Text]

22 Poelaert J, Depuydt P, De Wolf A, Van de Velde S, Herck I, Blot S. Polyurethane cuffed endotracheal tubes to prevent early postoperative pneumonia after cardiac surgery: a pilot study. J Thorac Cardiovasc Surg (2008) 135:771–6.[Abstract/Free Full Text]


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British Journal of Anaesthesia, 5 Feb 2009 [Full text]
Continuous control of endotracheal cuff pressure
Saad Nseir
British Journal of Anaesthesia, 12 Mar 2009 [Full text]
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