Ventilatory support for pulmonary failure of the head trauma patient.
Severe head trauma patients frequently develop pulmonary failure. The aetiology of this respiratory distress may be central (neurogenic pulmonary oedema, delayed neurogenic pulmonary dysfunction, abnormal respiratory patterns) or peripheral, due to chest trauma, multiple trauma or lung infection. Hypoxia and hypercarbia alter cerebral haemodynamics, increase intracranial pressure and cause secondary deterioration of neurological function. Ventilatory support is of utmost importance in supportive care of head trauma patients. Continuous mechanical ventilation and intermittent mandatory ventilation are most frequently employed. Hyperventilation is used to lower intracranial pressure and positive end-expiratory pressure (PEEP) is applied in lung disorders characterized by interstitial oedema and alveolar collapse. The effects of PEEP on cerebral perfusion pressure and on intracranial pressure depend on the interaction of pulmonary compliance, cerebral pressure/volume relationship and cerebral vascular autoregulation. High levels of PEEP may be deleterious in patients with altered cerebral autoregulation. High frequency ventilation theoretically has less influence on intrathoracic pressures and on cerebral haemodynamics but has not been shown superior in the respiratory support of severe head trauma patients.