Positive end expiratory pressure reduces intracranial compliance in the rabbit

Acute respiratory distress syndrome is commonly encountered in head- injured patients. Positive and expiratory pressure (PEEP) is useful in improving oxygenation. However, PEEP, by increasing intrathoracic pressure, decreases venous return, mean arterial pressure, and cardiac output and increases jugular vein pressure. There is conflicting evidence in the literature as to the potential effect of PEEP on intracranial pressure (ICP). The present study was undertaken to examine the effect of PEEP on ICP and intracranial compliance. Twelve male rabbits weighing 3.5-4.5 kg were used. The following parameters were monitored: arterial blood pressure, ICP (intraparenchymal Camino device), PaCO₂, and PaO₂. A space-occupying lesion was produced by inflation of a double lumen pediatric Swan-Ganz catheter placed over the right parietal dura. The amount of fluid required to reach the point of exponential increase of ICP was recorded at PEEP of 0 and 10 cm H₂O. The mean volume needed to reach the deflection point of ICP was significantly lower when PEEP was 10 cm H₂O compared to the value when PEEP was 0 cm H₂O (685 ± 48 vs. 883.3 2+ 46 μl, respectively; p < 0.01). The results of the present study indicated that PEEP of 10 cm H₂O decreases intracranial compensatory reserves for maintaining ICP at normal levels in the presence of an expanding intracranial mass.