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.
Data collection:
De-identified data will be recorded. Age, BMI ( body mass index), Charleston co-morbidity
index, baseline PPV, End-tidal CO2, SVI, VTI, post PLR, post fluid challenge, return to
baseline, PF ratio, PEEP (positive end-expiratory pressure), SOFA (sequential organ
function assessment) Score on the day of the test will be recorded.
Statistical Analysis:
Microsoft Excel will be used to record data on an institutional computer. Once the data
is collected, it will be exported for statistical analysis. Jamovi will be utilized for
statistical analysis. Baseline characteristics will be compared using a T-test if
normative distribution or non-parametric test such as Mann Whitney U test. Reliability
and accuracy will be detected using ROC curve assessment. In addition, the Youden index
approach will be utilized to identify cut-offs of each of the variables and their change.
(PPV, SVI,VTI and End tidal CO2). All the delta values will be compared with pearson
correlation with a scatter plot and line of identity. Agreement between variables will be
done using Bland-Altman analysis. If necessary, values will be transformed into Z scores.
For all comparisons, a p-value of <0.05 was considered significant.