[Effect of high-frequency ventilation on intracranial pressure]

The influence of respiratory frequency, tidal volume, inspiratory flow and ratio of inspiratory/expiratory time on ventilator-related intracranial pressure (ICP) fluctuations was studied in six patients with severe brain trauma. ICP fluctuations were found to be markedly reduced at frequencies of 20/min and usually eliminated at 30/min. We found an exponential correlation between ICP fluctuations and respiratory frequency, but there was no correlation between tidal volume and ICP. Central venous pressure amplitudes were found to be in linear correlation with respiratory frequency and tidal volumes as well. The amplitude of respiratory ICP fluctuations correlates with the length of expiratory time. Our findings demonstrate that artificial ventilation without ventilator-related fluctuations in ICP ("brain-protective" ventilation) may be performed by conventional volume-constant, time-cycled ventilators. To assess the therapeutic relevance of eliminating respirator-related fluctuations of the ICP course in brain-injured patients, we suggest that frequencies of 25-30/min and tidal volumes of 6-9 ml/kg body weight should be used.