Hypothesis: A validated technique to measure cardiac output (CO) using echocardiography is to calculate stroke volume from the product of LVOT area and LVOT VTI and multiplying the product with heart rate ( CO = SV x H/R; SV = LVOT area x LVOT VTI ). The LVOT diameter for an individual is more or less a constant measurement. Therefore using the formula mentioned above (SV = LVOT area x LVOT VTI), if the LVOT area is constant, then SV should be proportional to the VTI. This means if a PLR manoeuvre or fluid bolus helps to achieve a rise in SV, then it should be reflected in an increase in VTI as well. If this assumption is true, then an increase in the value of VTI from baseline after fluid challenge (10-15%), should identify a volume responsive patient.
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Whether a change in Doppler VTI before and after passive leg raising test (PLR) correctly reflects changes in stroke volume measured by CCO PA catheter
Timeframe: within 1 minute