Pneumonia is an important cause of morbidity and mortality in the older population. Aspiration is an important pathogenic mechanism for pneumonia in the elderly, and poor oral health and hygiene are increasingly recognized as a major risk factor.[10] VAP remains one of the most common nosocomial infections in the ICU, affecting approximately 10% to 40% of the patients on mechanical ventilation, with an overall mortality of approximately 13%.[11, 12] Patients with VAP need longer periods of ventilatory assistance and hospital stays, in addition to an increased level of care and the need for additional procedures and treatments.[8, 13] The diagnosis of VAP represents approximately US$40,000 of additional hospital costs per patient.[8, 13] Patients who develop VAP seem to have twice the risk of death compared to similar patients without VAP.[14] The percentage of patients on mechanical ventilation who developed VAP in our study (18.69%) was similar to the findings in the literature.
The oral cavity is an important source of bacteria that may cause lung infections, and several studies have associated the presence of oral biofilm with the development of VAP. Dental plaque, which is a complex biofilm relatively resistant to chemical control,[15] accumulates rapidly in the oral cavity of critically ill patients.[4] Dental plaque in hospitalized patients with chronic lung diseases may serves as a reservoir of bacteria known to cause nosocomial pneumonia in susceptible individuals.[16] The oral cavity of patients on mechanical ventilation contains high amounts of respiratory pathogens such as methicillin-resistant Staphylococcus aureus, Pseudomonas aeruginosa, and gram-negative bacilli.[17] These same pathogens were identified in the lungs of patients on mechanical ventilation who developed VAP.[18, 19] In a prospective study evaluating oral health and VAP development among 162 critically ill patients, Saenson et al. (2016)[20] found a strong association between poor oral health and increased risk for early-onset VAP. Munro et al. (2006)[5] reported that more dental plaque and lower salivary volume are correlated with a high rate of pneumonia. Azarpazhooh and Leake (2006)[21] also found that poor oral health significantly increases the risk of pneumonia, up to 9.6-fold. Nakajima et al. (2020) found that bacterial pneumonia, poor oral hygiene, and severe dry mouth were significantly associated with oral candidiasis.[22] We found a high incidence of dental-related problems among our patients; however, only coated tongue and oral bleeding were considered independent risk factors for the development of VAP. Oral bleeding may be a sign of biofilm-induced gingivitis or be secondary to traumatic ulcers. In addition, the presence of blood clots in the oral cavity in patients with oral bleeding may favour bacterial proliferation and increase the risk of VAP.
The coated tongue forms on the dorsal surface and includes keratin, food residue and bacteria attached to the tongue papillae.[23] The surface of the tongue dorsum is filled with papillae, which increases the area available for bacterial colonization and facilitates the accumulation of desquamated epithelium and food debris.[24] It represents an important reservoir for bacteria, including periodontopathic bacteria.[25] Patients with a coated tongue present a higher number of salivary bacteria than patients without this alteration, and several reports have indicated that tongue cleaning reduced the total number of these microorganisms.[26] In a study involving 71 edentulous elderly adults in nursing homes, those with a coated tongue demonstrated significantly higher salivary bacterial counts than those without it, suggesting that a coated tongue could be a risk factor for aspiration pneumonia.[27] Kageyama et al. (2018)[28] also reported that tongue microbiota is related to the risk of and death via aspiration pneumonia among elderly patients living in nursing homes. Dry mouth has been associated with a coated tongue and VAP.[29, 30]. In our study, we found a high incidence of coated tongue, representing 63.80% of all patients. It was also considered an independent risk factor for VAP development. These results reinforce the importance of adequate oral hygiene, including teeth and oral mucosa, especially the tongue. We know that in cases of illness, oral hygiene can be neglected.
Given that the microbiota of the oral cavity plays an important role in the development of VAP, some studies have indicated that the initiation of the topical application of antiseptic agents, such as chlorhexidine, before intubation reduces nosocomial infections.[18, 19] The value of chlorhexidine oral care has been studied extensively. A meta-analysis including 12 randomized studies encompassing 2341 patients reported a significant overall risk reduction in VAP in patients with chlorhexidine hygienization.[31] Oral hygiene with chlorhexidine has been proposed as one of the five components of a core set of interventions in the ventilator bundle defined by the Institute for Healthcare Improvement. In our patients, daily oral hygienization with chlorhexidine was performed but only after ICU admission, and most patients were intubated beforehand.
Some limitations of our study should be mentioned. First, the oral physical examination, which was difficult in some cases, mainly due to the tube and their securement devices. Second, the caries diagnosis is much more complex than just a visual physical examination, involving detection of active white-spot lesions and sometimes with the help of interproximal radiographs. So, in our study, only visible cavitation was considered, not taking into account which and how many teeth involved.
Besides, a cross-sectional study has some limitation, once the investigator measures the outcome and the exposures in the study participants at the same time. However, this methodology can be used to calculate the odds radio as a measure of association, and it has been used to evaluate risk-factors for pneumonia, including VAP.[32–34]
According to our results and within the limits of the study, we may conclude that the presence of a coated tongue and oral bleeding in the ICU admission could be considered markers of VAP development in critically ill patients. Proper maintenance of oral hygiene, especially the tongue, before intubation may lead to a decrease in the incidence of VAP in the ICU. This issue becomes even more important now in the current pandemic COVID-19 scenario, where more people are expected to need mechanical ventilation.