The main finding of this randomized controlled study ̶ coordinated by nurses of two surgical ICUs of the University Hospital of Nantes ̶ is that implementing an automated adjustment of Pcuff by the Tracoe Smart Cuff Manager™ in combination with intermittent manual adjustments was more effective to regulate Pcuff than a strategy with manual adjustments alone. Indeed, automated adjustment of Pcuff markedly decreased the rate of patients experiencing at least one underinflation episode and the incidence of detected episodes of underinflation. Importantly, the automated Pcuff adjustment strategy was not associated with a higher incidence of detected episodes of tracheal cuff overinflation.
Interestingly, despite the randomization, airway pressures were or tended to be higher in patients allocated to undergo manual Pcuff adjustments solely (Table 2). Since airway pressure is transmitted to Pcuff [13], this imbalance could have reduced the incidence of underinflation episodes among patients with manual Pcuff adjustments solely. In other words, assuming strictly identical airway pressure between the two groups, the protective effect of the Tracoe Smart Cuff Manager™ against underinflation episodes could have been even more prominent.
To avoid both microaspirations and tracheal damage, achieving a 24-hour balance between under- and overinflation of the tracheal cuff is desirable. The issue is not new. Indeed, from the 1970s, some modified endotracheal tubes were released onto the market for this purpose. One of these tubes housed a valve connected to a larger balloon than the standard pilot balloon. This regulating valve aimed at maintaining Pcuff close to 30 cm H2O [14]. This so-called Lanz system is the forerunner of the Tracoe Smart Cuff Manager™. One advantage of the latter relies on its ability to be connected to the standard port of most tracheal tube models (contrary to the Lanz system which is natively-embedded into one model of tracheal tube). To the best of our knowledge, no published study evaluated the Tracoe Smart Cuff Manager™. Overall, devices automatically regulating Pcuff were surprisingly poorly assessed. Indeed, besides some very preliminary reports of “home-made” devices [15], a dozen studies evaluated whether an automated device connected to the endotracheal tube effectively maintains Pcuff within an acceptable range (7,8,15,18–24). All these previous studies were single-center studies. They were uncontrolled [22], not randomized [17], of limited size (18 patients or less)[8, 16, 20, 22], experimental [13, 21] and/or tested non-commercialized devices [19, 22]. Although several very different devices have been tested, most of these studies have concluded that maintenance of Pcuff within the acceptable range was better achieved with an automated rather than an intermittent manual control of Pcuff, especially via the reduction of underinflation episodes. In their hallmark study, Nseir et al. went even further by demonstrating that implementing an automated Pcuff control reduced both the tracheal level of pepsin (suggesting a reduction of gastric content microaspiration) and the rate of ventilator-associated pneumonia [7]. Importantly, the reduction in the rate of underinflation episodes must not be at the expense of a potentially harmful increase in the rate of overinflation episodes. Unfortunately, one device [8] and possibly another one [19] were associated with a higher rate of Pcuff episodes above 30 cmH2O than routine care. Other drawbacks applying to some devices are worth mentioning: they are bulky and/or inconvenient (which encourages their disconnection before patient transport, a procedure at-risk of aspiration of oropharyngeal content), relatively expensive, need electric [16] or gas [23] supply. This may explain the lack of wide clinical use of automated Pcuff control. The Tracoe Smart Cuff Manager™ may overcome all these issues.
Limitations of the study
First, inherently to the nature of the tested intervention, caregivers could not be blinded to the randomization arm.
Second, the study was focused on the specific population of brain injured patients, and we mostly used one model of endotracheal tube. However, this population is of interest in the field of prevention of respiratory infections since it is prone to develop such infections because, among other reasons, prolonged median duration of mechanical ventilation [24, 25]. We therefore believe that focusing on this specific population should be seen as strength rather than limitation of this study. Therefore, relative caution should be exercised before extrapolating our findings to other settings or populations or even to other airway access devices. Furthermore, this population is also particularly prone to be deeply sedated (Table 1). Since the absence of sedation is independently associated with increased risk for cuff underinflation [5], one can hypothesize that the adjunction of the Tracoe Smart Cuff Manager™ to routine care in less sedated patients would have been associated with an even more marked reduction in the incidence of underinflation episodes than that herein reported. This hypothesis remains to be tested.
Third, Pcuff measurements were not collected continuously. Therefore, undetected episodes of under- or overinflation may have been overlooked. This would have impacted our conclusions if these undetected episodes of incorrect Pcuff were significantly more frequent in the automated adjustment group than in the manual adjustment group, i.e., an imbalance totally opposite to that observed for detected events. This hypothesis is therefore highly unlikely.
Fourth, in patients with automated Pcuff adjustment but not in patients from routine care group, we used a three-way stopcock. Of note, direct connection of the manometer to the endotracheal tube may be source of air leakage [27]. The use of the three-way stopcock may have limited the air leakage by connecting the manometer before opening the dedicated outlet. Therefore, some patients may have benefitted more from the use of the three-way stopcock than from the use of the Tracoe Smart Cuff Manager™. We chose to add the three-way stopcock to the Tracoe Smart Cuff Manager™ in order to avoid its disconnection (and therefore its necessary re-inflation) each time a manometer is connected, i.e., several times a day. This allowed direct Pcuff measurements, i.e., upstream of the Tracoe Smart Cuff Manager™ rather than using the dedicated inlet of the device (Fig. 1). Of note, the manufacturer proposes the direct connection of the Tracoe Smart Cuff Manager™ to the tracheal tube with no three-way stopcock, intermittent manometer Pcuff measurements being then performed via the dedicated inlet. Interestingly, with this latter approach, manometer connection-induced possible air leakage would slightly deflate the inner balloon of the device but, importantly, not the tracheal cuff. Therefore, when using the Tracoe Smart Cuff Manager™ with a three-way stopcock or not, manometer connection-induced deflation of the tracheal cuff is theoretically reduced. We believe this is a strength of the device. In the present study, using a three-way stopcock in both groups would have been helpful to delineate the specific contribution of the Tracoe Smart Cuff Manager™ and the three-way stopcock to our findings. However, adding a three-way stopcock to the endotracheal tube when no device for automated adjustment is connected is not recommended [24, 25] and is therefore neither wide current practice nor part of our routine care.
Fifth, in this study, manual adjustments were not guided by strict specific rules except correcting a Pcuff value outside the recommended range of 20–30 cmH2O. Indeed, the decision of manual adjustment and its magnitude tightly depends on previous measurements and adjustments in a given patient. Hence, several manual adjustments have consisted in modifying a Pcuff value already within this recommended range (from 21 to 27 cmH2O for instance) in a possibly unduly manner. This may explain the somewhat high incidence of manual adjustments in both groups (56% in the Tracoe Smart Cuff Manager™ group vs. 77% in the routine care group, p < 0.001). Since the Tracoe Smart Cuff Manager™ is able to inflate or deflate the tracheal cuff, these manual adjustments could have been unnecessary in patients equipped with this device. Indeed, less than 4% of Pcuff measurements lied outside the recommended range in this group.
Last, our study was not designed to assess whether the Tracoe Smart Cuff Manager™ reduces the incidence of ventilator-associated respiratory infections and therefore the ventilator free days, ICU length of stay or even mortality. Indeed, the Tracoe Smart Cuff Manager™ was not kept in place throughout the duration of invasive ventilation but only 48 hours in most patients, i.e., just the duration of the study observation period for its primary endpoint. The present study demonstrates that the Tracoe Smart Cuff Manager™ reduced the incidence of cuff underinflation. Whether this encouraging finding would translate into a reduction in ventilator-associated respiratory infections is not straightforward and deserves a dedicated study [19]. Indeed, a too rapid Pcuff correction by the automated device may interfere with the self-sealing mechanism of the cuff and may reduce its sealing characteristics, therefore exposing to microaspirations [28]. Interestingly, the Tracoe Smart Cuff Manager™ houses a valve aiming at slowing down the reaction time before Pcuff correction but its effectiveness has to be specifically assessed. Moreover, prevention of ventilator-associated respiratory infections is multifaceted and demonstrating a reduction in their incidence by acting on only one facet (reduction of underinflation episodes) may require a large study size. An ongoing multicenter study testing another pneumatic device may provide further insight on this relevant topic [29].