Rhinosinusitis involves inflammation of the sinonasal mucosa with impaired mucociliary clearance. Viral infection triggers mucosal edema that blocks sinus ostia, creating a hypoxic, stagnant environment conducive to bacterial colonization. Viral-bacterial synergy mechanisms include induction of local inflammation, obstruction of sinus ostia, increased bacterial attachment to nasal epithelial cells, and disruption of local immune defense. The aerobic bacterial phase involves S. pneumoniae, H. influenzae, and M. catarrhalis, while the anaerobic phase develops with prolonged obstruction featuring Peptostreptococcus, Prevotella, and Fusobacterium species. Phenylephrine, a selective alpha-1 agonist, decreases hydrostatic capillary pressure and reduces mucosal blood volume but does not directly reduce inflammation. Rebound congestion occurs through rapid tachyphylaxis, receptor desensitization, compensatory vasodilation, and inflammatory cell infiltration. The nurse performs comprehensive assessment, differentiates viral from bacterial presentations, implements protocol-based treatment, and coordinates care escalation.