Passive Leg Raise and Mini-fluid Challenge Effect on Various Cardiac Output Surrogates Such as Pulse Pressure Variation (PPV), End-tidal CO2 (Carbon Dioxide), Bioreactance (Stroke Volume Index -SVI) and Velocity Time Integral on Echocardiographic Exam for Fluid Responsiveness in Patients With Moderately Severe ARDS (Acute Respiratory Distress Syndrome)

Fluid responsiveness in patients with moderate to severe ARDS is crucial, as additional unnecessary fluid may be harmful. Various techniques of hemodynamic assessment exist, each with its own advantages and limitations. This study compares different techniques of preload responsiveness that include passive leg raise (PLR) and mini-fluid challenge induced changes in Pulse pressure variation (PPV), End tidal CO2, Bioreactance based Stroke volume index (SVI) and velocity time integral (VTI) on Echocardiogram.

Study protocol :

Baseline Echo with VTI will be obtained Bed side monitor will be set to display PPV and end tidal CO2 Baxter Starling system will be connected to the patient All baseline values will be recorded Tidal volume will be temporarily adjusted to 8 ml/kg , which will be reverted back to 6ml/kg after the measurements. This has proven to be a safe maneuver.

All the above hemodynamic assessments will be performed for eligible patients by measuring before and after PLR and repositioning to baseline. VTI will be estimated by bed side Echocardiogram. SVI will be estimated using the Starling system (Baxter). PPV and End tidal CO2 will be recorded from the bed side monitors.

Fluid responsiveness is presumed with a change in VTI of 10%. For these patients a mini-fluid challenge of 250 cc of crystalloids (NS, RL or Normosol) will be given over 10 min and PPV, VTI, End tidal CO2 and SVI will be recorded before and after fluid challenge. Patients with VTI change of < 10%, as non-responders, who will also be included in the analysis for assessment of reliability using the ROC curves. hemodynamic assessments and repeated fluid challenge will be considered as needed. Stability of vasopressor dose with maximum of 500 cc of crystalloid will be considered as positive fluid responder. This cohort of patients will be considered as gold standard for preload responsiveness and will be categorized based on a nominal scale. Patients who need higher vasopressor support despite 1L of crystalloid within 3 hours will be considered fluid non-responders.