Abstract
BACKGROUND: The role of chlorhexidine in oral care for mechanically ventilated elderly patients remains debated, particularly regarding its impact on oral microbiota and clinical outcomes. OBJECTIVE: To compare oral microbiota composition and prognosis among elderly mechanically ventilated patients receiving oral care with either chlorhexidine solution or normal saline. METHODS: Sixty intubated patients (≥ 65 years) were randomized to receive oral care with 0.12% chlorhexidine (intervention group) or 0.9% saline (control group) three times daily during mechanical ventilation. All patients underwent standardized oral hygiene during mechanical ventilation. Oral samples were analyzed by 16 S rRNA sequencing, with outcomes compared to oral health and clinical data. Secondary outcomes included dental plaque index, ventilator-associated pneumonia (VAP), 28-day mortality, patient outcomes, and oral complications. RESULTS: One week after intervention, the chlorhexidine group exhibited a significant decrease in oral bacterial diversity (Simpson index, P = 0.037). Despite this, no significant differences were observed in clinical infection symptoms-defined as fever, purulent airway secretions, elevated white blood cell count, or increased C-reactive protein levels requiring evaluation by the attending physician. All participants received standard ICU antimicrobial prophylaxis or therapy according to institutional protocols; no additional systemic antibiotics were initiated solely for oral or respiratory infections. There were no significant differences between groups in ventilator-associated pneumonia (VAP) incidence (P = 1.000), duration of mechanical ventilation (P = 0.063), ICU stay (P = 0.191), 28-day mortality (P = 0.82), or rates of complications and plaque formation. The chlorhexidine group also showed a decrease in dominant microbial taxa and an increase in specific anaerobic bacteria. CONCLUSION: Chlorhexidine temporarily altered oral microbiota composition without improving short-term clinical outcomes. Although no infections increased, its potential impact on microbial balance warrants caution, and larger studies are needed to validate these findings. TRIAL REGISTRATION: ClinicalTrials.gov ID NCT06691841. Registeration Date 23 September 2022, https://clinicaltrials.gov/study/NCT06691841 .