Ventilator-associated pneumonia (VAP) is the most frequent life-threatening nosocomial infection in the ICU. Oropharyngeal colonization with bacterial pathogens is the first step toward lung infection. Oral hygiene with Chlorhexidine mouth wash (CMW) is among the most widespread preventive measure to prevent VAP. Precise microbial documentation of CMW efficacy on oropharyngeal colonization is lacking. Investigators wish to determine CMW antimicrobial efficacy in ICU ventilated patients and to measure chlorhexidine residual concentration in patients' saliva at the same time-points after CMW.

Ventilator associated pneumonia (VAP) is the most frequent life-threatening nosocomial infection in the ICU. Oropharyngeal colonization with bacterial pathogens is the first step toward lung infection. Oral hygiene with Chlorhexidine mouth wash (CMW) is among the most widespread preventive measure to prevent VAP. Although many guidelines and expert opinions recommend oral hygiene with chlorhexidine, optimal conditions of CMW use remain unknown. In addition, precise microbial documentation of CMW efficacy on oropharyngeal colonization is lacking. Investigators wish to determine CMW antimicrobial efficacy in ICU ventilated patients and to measure chlorhexidine residual concentration in the saliva at the same time-points after CMW.

In the participanting unit, CMW is performed every 6 hours with a 0.12% chlorhexidine solution.

Hence, microbial oropharyngeal sampling will be performed 6h after the last CMW (and just before the next one), to assess oropharyngeal colonization and then 15 minutes, 1 hour, 2 hours, 4 hours, and 6 hours after a new CMW to assess CMW efficacy in terms of bacterial growth.

In a subset of patients, 0.5 mL of saliva will be collected with a syringe at the same time points, with an additional T30 time (at 30 minutes) to measure chlorhexidine concentration.

Inclusion Criteria:

• critically-ill patients admitted to the ICU and receiving invasive mechanical ventilation for more than 48 hours

Non-inclusion criteria:

• cervical or mouth surgery in the last 15 days;
• history of oropharyngeal neoplasm or of cervical or oropharyngeal radiotherapy,
• tracheotomy,
• age under 18

Exclusion Criteria:

• Patients whose samples retrieved less than 10 to the 3 colony forming unit (CFU)/mL bacteria and those who had two or more missing microbiological samples were secondarily excluded

- Consecutive critically-ill patients admitted to the ICU and receiving invasive mechanical ventilation for more than 48 hours