The impact of sedation on pulse pressure variation

ObjectivePulse pressure variations (PPV) are mainly influenced by ventilation. The impact of sedation on PPV is not known. The aim of the study was to test the influence of sedation on pulse pressure variation in mechanically ventilated critically ill patients and to compare PPV in critically ill and brain dead patients. Beside the absolute value of PPV, the adjusted values of pulse pressure were used to eliminate influence of ventilation.Design and interventionMechanically ventilated patients received four different breath frequencies. At each frequency airway pressure was adjusted to keep the end-tidal CO2 stable. In critically ill patients the frequencies were applied at basal (bispectral index – BIS median 38) and deeper sedation (BIS 29).Main outcome measuresSimultaneous haemodynamic and respiratory data including oesophageal pressure were recorded, adjusted PPV were calculated as PPV/VT, PPV/dPair, PPV/dPes where VT is tidal volume, dPair and dPes are airway and oesophageal driving pressures.SettingUniversity Hospital, ICU.Participants30 critically ill and 23 patients with a diagnosis of brain death.ResultsThe pulse pressure variation did not change significantly during deep sedation compared to basal sedation (median 10.3 vs 10.9%) whereas PPV/dPair increased from 0.7 to 0.8%/cm H2O and PPV/dPes from 1.9%/cm H2O to 2.4%/cm H2O (p = 0.04). Patients with a diagnosis of brain death had higher PPV and adjusted PPV than critically ill patients.ConclusionDeeper sedation increases values of adjusted pulse pressure variation.