Ventilator-associated pneumonia (VAP) develops >48 hours after endotracheal intubation and initiation of mechanical ventilation. The endotracheal tube (ETT) bypasses the natural defense mechanisms of the upper airway: the epiglottis, cough reflex, mucociliary clearance, and secretory IgA. The ETT cuff creates a sealed space above it where oropharyngeal secretions pool, forming a reservoir of pathogen-laden fluid. Microaspiration of these secretions around the cuff into the lower respiratory tract is the primary mechanism of VAP development—even well-inflated cuffs (25-30 cmH2O) do not prevent microscopic leakage through longitudinal folds in the cuff material. Early-onset VAP (within 4 days of intubation) is typically caused by community-acquired organisms (S. pneumoniae, H. influenzae, MSSA), while late-onset VAP (≥5 days) involves multidrug-resistant organisms (MRSA, Pseudomonas aeruginosa, Acinetobacter, ESBL-producing gram-negatives). The oropharyngeal flora shifts dramatically within 48 hours of ICU admission from normal flora to gram-negative bacilli colonization, providing the source organisms for aspiration. Biofilm forms on the inner surface of the ETT, creating a persistent bacterial reservoir that can shed organisms into the lower airway with each breath or suction pass.