In a previous issue of Critical Care, Nseir and colleagues presented an article regarding continuous control of endotracheal cuff pressure and tracheal wall damage 1.
Among the pathogenic mechanisms responsible for ventilator-associated pneumonia (VAP), oropharyngeal colonization by potentially pathogenic microorganisms and silent aspiration of subglottic secretions around the tracheal tube cuff seem to play a pivotal role 2. In order to prevent pneumonia, several approaches have been proposed – such as placing patients in the semirecumbent position 3, continuous aspiration of subglottic secretions (CASS) above the tracheal tube cuff 4, oropharyngeal decontamination by antiseptics 5, and the application of antiseptic-impregnated endotracheal tubes 6.
The key element of the proposed pathogenesis of VAP appears to be aspiration of colonized oropharyngeal and subglottic secretions. Appropriate control of the endotracheal tube cuff pressure (Pcuff) may therefore serve as a major prevention target. Intubated patients were recommended to be managed with Pcuff values between 20 and 30 cmH2O to provide a sufficient seal without compromising mucosal perfusion 7. The routine management of cuff inflation consists of periodic manual checking of the Pcuff, which does not ensure the appropriate maintenance of the Pcuff during continuous tracheal intubation 8. Moreover, the manual checking of the Pcuff may cause either overinflation or deflation of the cuff and may cause aspiration of contaminated secretions to the lower airway during the manoeuvre. Leaks and loss of Pcuff are frequent in intubated patients, and a persistent Pcuff below 20 cmH2O was an independent risk factor for VAP in one study 8. Consequently, appropriate maintenance of pressure of the tracheal tube cuff is recommended in recent guidelines 9.
In a previous issue of the journal, Nseir and coworkers describe a pneumatic device for the continuous control of the Pcuff in an animal model 1. The aim of the study was to assess whether the continuous control of the Pcuff results in reduced tracheal ischaemic lesions in mechanically ventilated piglets. For this purpose, the authors compared the pneumatic device with the manual control of Pcuff in a randomized trial. The pneumatic device provided effective continuous control of the Pcuff, with longer periods of Pcuff within the target values than piglets managed with manual control. This device is therefore potentially useful for clinical practice in order to avoid both excessive inflation and deflation of the cuff. Hyperaemia and haemorrhages in the trachea were observed at the cuff contact area in all animals, however, with no differences between animals with and without the pneumatic device.
Several devices that provide an automatic and continuous effective control of the Pcuff have been described in the literature. Most of these devices are not automatic, some devices need frequent control by the attending staff, and other devices operating in a more automatic and continuous way are complex, requiring the use of special and expensive equipment that may not be available routinely 10. It is probable that these issues concerning complexity and cost could explain the lack of continuous automatic control of cuff inflation in clinical practice.
We have described a simple and cheap device that is very effective for the routine maintenance of adequate cuff inflation during mechanical ventilation that does not require any specific equipment 11. A recent randomized clinical trial in mechanically ventilated patients comparing this device with the routine manual control of cuff inflation, however, showed no benefits in the prevention of VAP 12. These findings suggest that other factors than cuff inflation influence the microaspiration of secretions to the lower airways around the tracheal tube cuff. Commercially available high-volume low-pressure tracheal tubes such as those used in the study often form folds around the cuff, hence allowing leakage of secretions pooled above the tube cuff in studies in vitro, even at Pcuff levels similar to those used by Nseir and colleagues in piglets 13. Several devices have consequently been recently developed in order to overcome this problem. Among those devices, the Microcuff endotracheal high-volume low-pressure tube features an ultrathin (7 μm) poly-urethane cuff membrane around an inner conventional inflatable cuff. This tube is effective in preventing fluid leakage around the cuff in an in vitro setup 14. The combination of this device with CASS is effective in preventing both early-onset and late-onset VAP in a recent clinical study 15.
One of the potential concerns of all these devices, particularly CASS, is the potential damage of the tracheal wall. In an animal sheep model, Berra and colleagues demonstrated important tracheal lesions when using CASS 16. We do not know whether this is applicable to humans. In the study by Nseir and colleagues, the tracheal lesions found could be explained, at least in part, by the high inflation pressure they applied eight times daily via 50 ml during 30 min. This is not the current clinical practice in humans, and after this study it should be completely avoided.