The use of a novel cleaning closed suction system reduces the volume of secretions within the endotracheal tube as assessed by micro-computed tomography: a randomized clinical trial

Endotracheal intubation is a necessary choice to ventilate many critically ill patients; however, the use of an endotracheal tube (ETT) is associated with several complications [1]. The presence of secretions within the ETT has been advocated in the pathogenesis of ventilator-associated pneumonia (VAP) since many years [2]. Soon after intubation, in the ETT is detectable a layer of biofilm composed by mucosal secretions, erythrocytes, neutrophils, and possibly microbes [3]. The ETT biofilm thickness increases with time and airflow can transport microbial aggregates towards the distal airways, leading to pneumonia [4]. The link between ETT biofilm and VAP has been well established: the prevention of biofilm formation or its removal through modified ETTs has been associated with reduced incidence of VAP in the clinical scenario [5]. Standard care is not adequate to completely remove secretions from the ETT and several additional measures aimed to reduce ETT biofilm have been proposed to prevent VAP [6].

The presence of secretions within the ETT is also potentially associated with obstruction and increased resistance to airflow. Specifically designed devices (i.e., the Mucus Shaver) are able to mechanically remove secretions from the inner ETT surface, maintaining ETT patency and reducing ETT bacterial colonization [7]. In difficult to wean patients, restoring airway resistance to nominal values through ETT secretion removal might represent a clinically relevant advantage.

In this randomized trial, we evaluated the efficacy of a cleaning closed suction system (CSS), a device designed to combine a closed suction catheter and an ETT water-based cleaning system. The device is designed to be used several times for all the duration of intubation, with the aim of keeping the ETT free from secretions and therefore the potential advantage of lower ETT microbial colonization and lower resistance to airflow. We hypothesized that patients treated with the cleaning CSS would have, at the moment of extubation, a lower amount of secretions within the ETT as compared to controls treated with a standard CSS. We measured the volume of secretions present in the ETT after extubation using Micro-computed tomography (MicroCT), a reliable technique able to measure the amount of secretions of a large part of the ETT [8].

Forty patients were studied; 26 were successfully extubated, 12 died and ETTs were removed post-mortem, one had an unplanned extubation, one had a failed extubation and required reintubation, and none underwent tracheostomy. In total, we collected data on 252 ventilator days; nearly a thousand of tracheal suction maneuvers and more than 300 cleaning maneuvers were performed during the study. The nurses in charge of the patients did not report any relevant adverse event related to the use of the cleaning CSS, neither reported any major issue that prevented the correct use of the device. Sudden ETT occlusion requiring emergent bronchoscopy occurred in one patient in the treatment group and one patient in the control group; in both cases, after bronchoscopy, the ETTs were removed and the patients were re-intubated.

Secretions within the ETT

The volume of secretions present in the ETT at extubation was reduced in the treatment group, as compared to controls (p = 0.001, Table 2). Correspondingly, the ETT cross-sectional area occupied by secretions was six times lower in the treatment group, as compared to controls (p = 0.001, Table 2). Secretions amount in the control group increased from the ventilator to the tip side, while in the treatment group the regional distribution of secretions along the ETT was different, resulting lower and fairly constant along the entire ETT (p < 0.001 for treatment effect, p = 0.005 for the interaction between the treatment effect and the region effect by ANOVA, see Fig. 2a for post hoc tests).

	All patients, n = 40	Control group, n = 20	Treatment group, n = 20	P value
Study ETT in place, days	5 (3–8)	5 (3–7)	5 (3–10)	0.512
ETT secretions, volume (mL)	0.274 (0.046–0.576)	0.568 (0.162–0.756)	0.081 (0.021–0.306)	0.001
Average CSA reduction  (%)	3 (1–6)	6 (2–10)	1 (0–3)	0.001
Tracheal aspirate cultures, log (CFU)	0 (0–5)	0 (0–3)	0 (0–5)	0.234
ETT colonization, log (CFU)	2 (0–4)	2 (0–4)	1 (0–4)	0.568
Leukocytes in ETT lavage, n. pos. (%)	6 (15)	6 (30)	0 (0)	0.019

ETT endotracheal tube, CSA cross-sectional area, CFU colony forming units, n. pos. number of ETT lavage samples positive for leukocytes presence

Analyzing the local cross-sectional area reduction in ETT slices of 0.5-mm thickness, the peak average lumen reduction was lower in the treatment than in the control group (3 ± 4.4 vs. 9.5 ± 8 %, p = 0.003, Fig. 2b). Considering the maximum local cross-sectional area reduction, none of the ETTs in the treatment group showed a lumen reduction over 20 % (maximum cross-sectional area reduction 17 %) at the moment of ETT removal. Instead, half of the patients in the control group had their ETTs showing a maximum cross-sectional area reduction of more than 20 % of the nominal value (maximum 34 %, p < 0.001 for a cut-off of 20 % maximum cross-sectional area reduction in comparison with treatment group).

In this randomized clinical trial, we showed that the regular use of a cleaning CSS is effective to reduce the volume of secretions present in the ETT at extubation, as assessed by MicroCT scan. We evaluated the effectiveness of a novel device in the everyday practice of a general ICU, excluding patients whose risk of ETT displacement was too high for safety reasons, since we had no previous data available about the clinical use of the cleaning device. The presented data suggest that no specific limitation should be present for the use of such a cleaning CSS. We chose the volume of secretion present at extubation as the primary endpoint because the device was primarily designed to remove secretions, either by aspiration or cleaning. We reasoned that establishing its efficacy in this respect should be preliminary to investigating any clinical endpoint. Moreover, the volume of secretions in the ETT was an endpoint which we could assess with high precision, as previously described by our group using a novel technique such as MicroCT scan [8]. MicroCT, in comparison with other techniques proposed for the measurement of the amount of secretions within the ETT, allowed us to directly study a large portion of the ETT (20 cm) with a fairly high resolution (35 μm).

The device we used is not the first cleaning system based on the retraction of an inflated balloon. Other similar devices were studied in the past, and showed good effectiveness [13, 14]. However, those devices were designed with the sole purpose of cleaning the ETT, requiring patient disconnection from the ventilator circuit. The novelty of the device used in this study is that the cleaning system is embedded in a closed suction system resembling the one commonly used in our ICU for tracheal suction in patients expected to be ventilated for several days. The advantage of using a closed system is that patient disconnection is not required to perform both suction and cleaning maneuvers, and positive pressure is preserved in the airways. Moreover, airways contamination is reduced, and some guidelines recommend the use of such systems [15–18]. Thus, the study device offered features similar to the standard of care in our ICU, with the added benefit of ETT cleaning.

The patients enrolled in the study were representative of a general ICU population, including both surgical and medical patients. The analyzed ETTs were similar in the two groups, both in terms of size (Table 1) and number of days they remained in place (median 5 days, Table 2). In the control group, we report a cross-sectional area reduction similar to data available in the literature [8, 19, 20]. Despite the use of the cleaning device, the ETTs in the treatment group did not result completely free from secretions, for several reasons. First, the efficacy of the cleaning system might not be optimal in some patients, possibly due to different physical properties of the secretions (i.e., density, adhesion to the plastic surface) and to the presence of an amount of biofilm which is difficult to remove [21]. Second, in some patients, more than three cleaning maneuvers might be needed to preserve patency of the ETT. Future studies might investigate if a different protocol based on patients’ needs (i.e., equal number of cleaning and suction maneuvers) is more effective. Third, we did not clean the ETT immediately before extubation, and some secretions might have gathered within the ETT after the last cleaning maneuver was performed or during the extubation procedure. We decided not to perform a cleaning maneuver before extubation to have a better understanding of the effects of the cleaning device on ETT patency during a real ICU shift, rather than immediately after cleaning, adding strength to our results.

As we previously showed, the tip side is the part where secretions tend to collect, both because of the proximity with trachea, where secretions gather, and because that ETT part is the more dependent when the patient lies in the semi-recumbent position. We showed that the lack of secretion in the proximal, visible part of the ETT does not exclude a relevant loss of cross-sectional area in the endotracheal portion, whose presence can be clinically disclosed only by bronchoscopy. We showed that the use of a cleaning device reduces the loss of internal diameter, and the preventive effect is particularly evident in the tip side. This finding is consistent with the finding of reduced airflow resistance associated with the use of the novel CSS.

We could not demonstrate any difference in ETT pathogen colonization between the treatment and the control groups, a finding previously reported with other ETT cleaning devices [7]. The cleaning balloon is designed to maintain ETT patency, but a thin layer of contaminated biofilm could remain on the ETT surface resulting in positive cultures when colonization is assessed by lavage of the entire ETT. Future studies might investigate if ETT colonization can be reduced by cleaning balloons of different shape or using moisturizing solution other than saline. However, we report a reduced amount of leukocytes in ETT lavage fluids obtained from the treatment group. We might speculate that the use of a cleaning device results in a reduced inflammatory stimulation of the mucosa, reflected by a lower amount of leukocytes in the ETT biofilm, lower mucosal fragility and reduced production of secretions, leading to a lower need for suction and less mucosal injury. Such findings, if confirmed, might be clinically relevant because lower production of secretions can lead to lower risk of sudden ETT obstruction and lower increase of airways resistance due to loss of ETT patency.

Regarding the major clinical outcomes, the present study was neither aimed, nor powered to demonstrate differences in mortality, ICU ventilator free days or VAP/VAE incidence. Similarly, we could not find any difference in mCPIS, a clinical score associated with presence of lung infection. A larger population is needed to investigate those outcomes, and is debatable if a single component of ETT care, such as a cleaning catheter, is able to significantly impact the clinical course of critically ill patients. Based on the results of this study, the use of a cleaning catheter appears safe and no relevant contraindication to its use emerged. However, the relevance of the endpoints investigated in this study is not sufficient to mandate a change in the current practice and a routine use of such cleaning catheters in every intubated patient.

In this randomized clinical study, we report that the regular use of a cleaning CSS is effective in reducing the amount of secretions present in the ETT at extubation, particularly in the part closer to the trachea. The reduction of secretions in the ETT was associated with lower resistance to airflow in a subset of patients. We report no relevant adverse events related to the use of the cleaning device other than the ones known to be associated with standard suction. Studies on larger populations are needed to prove the relevance of the use of a cleaning catheter on major clinical outcomes.