Respiratory mechanics in brain-damaged patients
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To assess respiratory mechanics on the 1st and 5th days of mechanical ventilation in a cohort of brain-damaged patients on positive end-expiratory pressure (PEEP) of 8 cmH2O or zero PEEP (ZEEP).
Design and setting
Physiological study with randomized control trial design in a multidisciplinary intensive care unit of a university hospital.
Patients and measurements
Twenty-one consecutive mechanically ventilated patients with severe brain damage and no acute lung injury were randomly assigned to be ventilated with ZEEP (n = 10) or with 8 cmH2O of PEEP (n = 11). Respiratory mechanics and arterial blood gases were assessed on days 1 and day 5 of mechanical ventilation.
In the ZEEP group on day 1 static elastance and minimal resistance were above normal limits (18.9 ± 3.8 cmH2O/l and 5.6 ± 2.2 cmH2O/l per second, respectively); on day 5 static elastance and iso-CO2 minimal resistance values were higher than on day 1 (21.2 ± 4.1 cmH2O/l; 7.0 ± 1.9 cmH2O/l per second, respectively). In the PEEP group these parameters did not change significantly. One of the ten patients on ZEEP developed acute lung injury. On day 5 there was a significant decrease in PaO2/FIO2 in both groups.
On day 1 of mechanical ventilation patients with brain damage exhibit abnormal respiratory mechanics. After 5 days of mechanical ventilation on ZEEP static elastance and minimal resistance increased significantly, perhaps reflecting “low lung volume” injury. Both could be prevented by administration of moderate levels of PEEP.
KeywordsMechanical ventilation Head injury Hypocapnic bronchoconstriction Ventilator-induced lung injury
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