Influence of PEEP on cerebral blood flow and cerebrovascular autoregulation in patients with acute respiratory distress syndrome.

Background: High levels of positive end-expiratory pressure (PEEP), as part of the treatment in patients with acute respiratory distress syndrome (ARDS), may prevent alveolar collapse and maintain oxygenation. PEEP potentially reduces cerebral venous return, increases intracranial blood volume, and may, therefore, affect cerebral blood flow (CBF) and cerebrovascular autoregulation (AR). This study investigates the effect of PEEP on CBF and AR in patients with respiratory failure. Methods: CBF velocity was measured using transcranial doppler and correlated with the invasive arterial blood pressure curve to calculate the index of AR Mx (Mx > 0.3 indicates impaired AR). Mx was measured at lower PEEP levels and after increasing PEEP. Only an increase of Mx of > 0.2 was considered to be clinically relevant. Two 1-sided Wilcoxon tests. Results: Twenty mechanically ventilated patients with ARDS were included. Elevation of PEEP from 9.2 +/- 1 to 14.3 +/- 1 cmH(2)O did not influence CBF velocity but increased Mx from 0.317 +/- 0.35 to 0.414 +/- 0.32 (difference <= 0.2). Mx was > 0.3 in 11/20 patients during baseline measurements, indicating impaired AR. Conclusions: Surprisingly, AR was impaired in 55% of the patients with ARDS. This should be taken into account when managing cerebral perfusion pressure to avoid cerebral hyperperfusion or hypoperfusion. Increasing PEEP from 9.2 to 14.3 cm H2O had no further clinically relevant effect on AR, independent of preexisting AR impairment.