Ventilator-Associated Pneumonia (VAP) in Neurocritical Patients: The Hidden Dialog of Brain and Infection

Abstract

Patients with multiple traumas, particularly those with traumatic brain injury (TBI), are among the most challenging cases in intensive care medicine. Although early orotracheal intubation and invasive mechanical ventilation (IMV) are essential for airway protection and neurological treatment, they significantly increase the risk of lower respiratory tract infection (LRTI), including ventilator-associated pneumonia (VAP) and ventilator-associated tracheobronchitis (VAT). These complications are particularly prevalent among neurocritical patients due to the distinctive interaction between the brain, lungs and immune system. This narrative review examines the current evidence on the mechanisms underlying the brain–lung–immune axis; the diagnostic challenges in identifying respiratory infections in mechanically ventilated TBI patients; and optimal approaches to empirical or quasi-targeted antimicrobial therapy based on diagnostic algorithms and rapid molecular techniques. Severe TBI induces neurogenic inflammation, autonomic dysregulation, and immunosuppression, thereby increasing susceptibility to pulmonary infections. The ‘triple hit hypothesis’ best explains this cascade: sympathetic hyperactivity (first hit), iatrogenic ventilatory injury (second hit), and intestinal dysbiosis with systemic immune dysregulation (third hit). VAP diagnosis remains challenging due to the lack of universal criteria, the overlap with systemic inflammatory response syndrome, and the low specificity of radiological and clinical signs. VAT may represent an intermediate stage within a continuum of ventilator-associated infection. Recent evidence supports the selective use of nebulized antibiotics for VAT, advocating an individualized, locally adapted empirical approach to VAP treatment. Syndromic molecular panels can accelerate the identification of pathogens, enabling the earlier and more appropriate selection of antimicrobials and improving outcomes while preserving stewardship. Understanding the brain–lung–immune axis and improving diagnostic accuracy are essential to enhancing the treatment of respiratory infections in neurocritical care. Integrating clinical assessment, biomarkers and rapid microbiological testing enables timely, targeted therapy and reduces the misuse of antimicrobials.