Respiratory mechanics in brain injured patients Clinical relevance

BACKGROUND: Brain injured patients have an increased risk of extracerebral organ failure, mainly pulmonary dysfunction. The prevalent cause of pulmonary failureis ventilator associated pneumonia (VAP) which increases morbidity and mortality.The respiratory dysfunction is mainly characterized by the presence of alveolarconsolidation of the dependent lobes.
METHODS: We investigated the mechanical changes of the respiratory system and theeffects of positive end-expiratory pressure (PEEP) in 10 normal subjects, in 10brain injured patients without respiratory failure and in 10 brain injuredpatients 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 injuredpatients independently from the presence of respiratory failure; 3) in braininjured patients with respiratory failure application of 15 cmH2O of PEEPincreased the Elastance of the Lung (Est,L), Est,rs and Rmax,L, while did notresult in significant alveolar recruitment and oxygenation improvement.
CONCLUSIONS: In conclusion, in brain injured patients 1) the respiratorymechanics is altered; 2) PEEP is uneffective to improve respiratory function inrespiratory failure due to ventilator associated pneumonia. Further studies arewarranted to better elucidate the pathophysiology and clinical management ofrespiratory dysfunction in brain injured patients.