The effect of tidal volume on fluid responsiveness assessment using pulse pressure variations and velocity time integral variations in patients with septic shock

Abstract

Introduction Expanding volume in septic shock can be a source of therapeutic dilemma. On one hand, the severity of the disease necessitates administration of fluids. On the other hand, it has now been clearly demonstrated that fluid overload has bad consequences. Many parameters were introduced to assess fluid responsiveness in patients with septic shock such as pulse pressure variations (PP%) and velocity time integral variations (VTI%). Objective The aim of this study was to determine whether the change in tidal volume introduced to patients with septic shock on mechanical ventilation would affect the values of PP% and VTI% of fluid responsiveness. Patients and methods In this prospective observational study, 60 mechanically ventilated patients with septic shock were enrolled. On admission, all patients received sedation and muscle relaxant to avoid any spontaneous breath. A fluid challenge in the form of 400 ml of normal saline 0.9% was given to all patients. However, before giving the normal saline to the patient, PP% and VTI% were measured when patient was given tidal volume 6 ml/kg and then when patient was given tidal volume 10 ml/kg. The same measures were repeated with the same tidal volumes, 1 min after giving the normal saline. Results A total of 31 patients were identified as fluid responders, whereas 29 patients were fluid nonresponders. In responders, the mean value of change of PP% with fluid challenge decreased significantly when increasing tidal volume from 6 to10 ml/kg, whereas the mean value of change of VTI% decreased insignificantly with tidal volume change. Conclusion PP% could be a reliable predictor of fluid responsiveness in patients with septic shock on a higher tidal volume ventilation, unlike VTI% which could be reliable at low tidal volume.