Maintaining the internal cuff pressure within the recommended range of 25–30 cmH₂O can reduce the aspiration of oropharyngeal secretions [13].

An internal cuff pressure less than 20 cmH₂O may promote the drainage of oropharyngeal secretions, while an excessive cuff pressure higher than 30 cmH₂O against the tracheal wall may cause a lesion of the mucosa; in fact, the normal tracheal mucosa capillary perfusion pressure is estimated to be around 30 cmH₂O.

Therefore, it is evident that cuff overinflation can produce tracheal ischemia, especially in critically ill patients whose peripheral capillary perfusion may already be impaired. A potential benefit could be to maintain a known constant level of cuff pressure.

Two randomized controlled trials tested two devices for the continuous control of tracheal pressure.

In the trial of Valencia et al., 142 patients, within 24 h of intubation, were randomly allocated to undergo continuous regulation of the cuff pressure with the automatic device or routine care of the cuff pressure. Pressure values were recorded every eight hours in both groups.

Despite the cuff pressure was better controlled using the automatic device, no differences were found between the two groups in terms of the onset of VAP, mortality, and ICU and hospital stay [15].

More recently, Nseir et al. conducted a trial on 122 patients on mechanical ventilation for more than 48 h to evaluate the efficacy of the continuous control of the endotracheal tube (ETT) cuff pressure by a pneumatic device versus manual control with a manometer every 8 h. In this study, the microaspiration of gastric contents, defined by the presence of a significant level of pepsin in tracheal aspirates, was significantly lower in the intervention group as well as the tracheal bacterial concentration and the VAP rate compared with the control group [14].

However, it is important to remember that coughing and even slight movements of the endotracheal tube either due to patient moving or caregiver handling the endotracheal tube should require rapid adaptation of pressure cuff by automatic devices in order to limit the risk of microaspiration of overhanging secretions.

The placement of the ETT through the vocal cords and into the trachea promotes the aspiration of oropharyngeal secretions composed of either oral flora and/or gastric contents. In intubated patients oropharyngeal secretions accumulate above and below endotracheal cuff facilitating the drainage into the lower airways [13]. In the first case, secretions easily drain into the subglottic space, pooling around the outer superior surface of the ETT cuff, progressively organizing in a thickening layer. These layers are found early after intubation and are rich in oral pathogens that can leak through the cuff and the tracheal mucosa into the lower airway. Recently, a strategy to prevent this occurrence has been developed consisting in subglottic secretion drainage (SSD) obtained by an ETT with a small suctioning port opening on the upper surface of the cuff. The suctioning can be applied in either a continuous or an intermittent fashion.

The effectiveness of this strategy in preventing the incidence of VAP seems to be demonstrated, despite the small number of randomized trials and the concern about the risk of tracheal mucosal damage.

A recent meta-analysis that included 13 randomized clinical trials with a total of 2,243 patients found that the subglottic secretion drainage was associated with a relative reduction in the incidence of VAP in patients requiring more than 24 h of intubation, with a reduction in the duration of mechanical ventilation and ICU length of stay and delayed VAP onset. However, it did not improve intensive care or hospital mortality [16].

Currently, the use of endotracheal tubes with subglottic secretion drainage should be taken into consideration as a VAP preventive strategy, to reduce the duration of mechanical ventilation and ICU stay, although further studies are needed to evaluate the best method of administration (continuous or intermittent) and the real risk of tracheal mucosal damage.

After a few days of mechanical ventilation, the lumen of the endotracheal tube is coated with a thick layer of biological material that is a favorable medium for bacteria adhesion and growth [17].

The most common nosocomial pathogens cultured from the lumen of the endotracheal tube are Staphylococcus aureus (including methicillin-resistant strains), group A Streptococcus, Acinetobacter, Moraxella catarrhalis, Haemophilus influenzae, and Pseudomonas aeruginosa [18, 19].

Once this biofilm has formed, aggregates of bacteria can easily come off into the lower airways during the suctioning maneuvers or bronchoscopy or by gravity or by the effect of the inspiratory gas flow [17].

It was demonstrated that 70 % of VAP patients have the same pathogens in tracheal secretions and endotracheal biofilm that, therefore, represent a potential source of colonization and infection of the lower respiratory tract [20].

Many efforts have been made to prevent the formation of the endotracheal biofilm. Several studies investigated the use of endotracheal tubes coated with antimicrobials or heavy metals, that is, silver, to contrast the formation of the biofilm.

The coating with polymers containing silver ions has bacteriostatic properties as the silver ions penetrate the bacterial membrane and interfere with DNA synthesis and then with bacterial replication.

New kinds of coatings seem to have a higher antimicrobial activity, but their clinical use is currently under development [21].

Up to now only silver-coated endotracheal tubes have been tested in clinical trials.

The North American Silver-Coated Endotracheal Tube (NASCENT) Investigation Group conducted a large multicenter randomized controlled clinical trial enrolling 1,509 patients intubated for more than 24 h randomized to receive a standard tube or a silver-coated endotracheal tube. Kollef et al. found that the silver-coated endotracheal tubes reduced the incidence of VAP and delayed the onset of the infection. However, their use was not demonstrated to reduce mortality rates, duration of intubation, or ICU or hospital length of stay [22].

The Mucus Shaver is advanced to the distal endotracheal tube tip, inflated, and subsequently withdrawn over a period of 3–5 s to remove the biofilm. Initially, it has been tested in mechanically ventilated sheep [23], and recently it has been studied in a randomized controlled clinical trial. At the extubation, only 8 % of the ETT from the Mucus Shaver Group was internally colonized by pathogens versus 83 % in the control group [24].

The effect of replacing the endotracheal tube with a tracheostomy on the incidence of VAP has been analyzed in several studies. In a meta-analysis of Griffith and colleagues [29], data from 5 randomized controlled trials with a total of 382 enrolled patients showed that early tracheostomy (<7 days) did not reduce the risk of VAP or mortality despite beneficial effects in terms of reduction of mechanical ventilation and hospital and ICU length of stay [25]. Furthermore, in a more recent study, early tracheostomy (<4 days) did not provide any effect on VAP incidence, duration of mechanical ventilation, hospital stay, or mortality [26].

After a prolonged intubation, a tracheal colonization by the same bacteria often resident in the oral cavity has been demonstrated, and the gastric enzyme, pepsin, may be detected in trachea–bronchial aspirates.

Bacterial load presented in the teeth, gums, tongue, and oral mucosa is different between healthy patients and patients treated with antibiotic therapy or immunocompromised. In patients affected by VAP, the same bacteria are often present in the distal airways, stomach, and oropharynx [27].

This suggests that the draining of saliva or gastric contents, below endotracheal tube cuff, determines the colonization of the tracheal mucosa, causing pneumonia.

The use of acid-suppressive medications that increase the gastric pH promotes the bacterial growth in the stomach, increasing the risk of tracheal colonization in case of aspiration of gastric contents. A study enrolling 60,000 patients showed an increased risk of nosocomial pneumonia when acid-suppressive medications are administrated [9].

Despite of this, we cannot provide definitive recommendations on the use of anti-acids in relation to VAP in the ICU setting. Furthermore, the bundle for VAP prevention published by the Institute for Healthcare Improvement still suggests stress ulcer prophylaxis [9, 28].

Given the etiology of VAP, a selective digestive tract decontamination (SDD) with antiseptics has been proposed.