Respiratory mechanics in brain injured patients.

BACKGROUND: Brain injured patients have an increased risk of extracerebral organ failure, mainly pulmonary dysfunction. The prevalent cause of pulmonary failure is ventilator associated pneumonia (VAP) which increases morbidity and mortality. The respiratory dysfunction is mainly characterized by the presence of alveolar consolidation of the dependent lobes. METHODS: We investigated the mechanical changes of the respiratory system and the effects of positive end-expiratory pressure (PEEP) in 10 normal subjects, in 10 brain injured patients without respiratory failure and in 10 brain injured patients with respiratory failure (PaO2/FiO2 lower than 200 mmHg) due to VAP. RESULTS: We found that: 1) Intra-Abdominal Pressure (IAP) was increased in brain injured patients with or without respiratory failure compared to normal subjects; 2) the Elastance of respiratory system (Est,rs), the Elastance of the chest wall (Est,cw) and Resistance max of the Lung (Rmax,L) increased in brain injured patients independently from the presence of respiratory failure; 3) in brain injured patients with respiratory failure application of 15 cmH2O of PEEP increased the Elastance of the Lung (Est,L), Est,rs and Rmax,L, while did not result in significant alveolar recruitment and oxygenation improvement. CONCLUSIONS: In conclusion, in brain injured patients 1) the respiratory mechanics is altered; 2) PEEP is uneffective to improve respiratory function in respiratory failure due to ventilator associated pneumonia. Further studies are warranted to better elucidate the pathophysiology and clinical management of respiratory dysfunction in brain injured patients.