STROKE VOLUME OPTIMISATION
The optimisation of SV with fluid is based on the theory of the Frank-Starling curve. The Frank-Starling law describes the relationship between end-diastolic volume (i.e., preload) and the ejected SV. Therefore, in response to a fluid challenge:
- An increase in SV >10% following a rapid fluid challenge (i.e., <5 min) indicates the patient is on the lower portion of their individualised Frank-Starling curve and is therefore not optimally filled.
- An increase in SV <10% following a rapid fluid challenge (i.e., <5 min) indicates the patient is on the mid or upper portion of their curve and is therefore well filled.
Guiding fluid management using the ODM+ is based on the administration of a fluid bolus and the measurement of the corresponding change in Doppler SV (< or >10%). This technique is unique to the Doppler technology and is evidence-based .
The minimum change in SV required to be effective at guiding SVO is dependent on the precision of the technology. A more precise technology is able to detect smaller changes in SV in response to an intervention (e.g., fluid challenge) while allowing the user to remain highly confident that a real change has occurred, and that change is not simply due to measurement error. Oesophageal Doppler technology is highly precise. With a focussed signal, 99% of the time a 10% change in SV is seen as significant and an actual increase in the patient’s SV has occurred. Other CO measurement techniques with a lower precision (higher coefficient of variation) may not be effective in using this algorithm (10% change in SV) in assessing the response to a fluid challenge.
The precision of the oesophageal Doppler also enables the detection of changes in SV in response to small (200-250 mL) boluses of fluid. These small fluid boluses enable the clinician to finely-tune fluid volume based on individual patient need. Technologies with poorer precision may need to use larger fluid challenges (e.g., 500 mL) and look for larger changes in SV (e.g., >15%) in order to determine whether the patient in fluid responsive, which may result in over filling.
In the examples across, the average patient requires 565 mL of protocol (bolus) fluid (based on an average from the ODM outcome studies). The administration of three 200 mL boluses results in the treatment of this patient’s hypovolaemia without significant overload (Figure 1). Compare this to the second example (Figure 2) whereby the same patient was administered two 500 mL fluid boluses. As a result, they received >400 mL of unnecessary fluid.
SVO guided by the precision of the ODM is the only algorithm + technology combination to consistently demonstrate improvements in patient outcome.
Stroke Volume Optimisation with a precise technology enables the administration of small (200 mL) fluid boluses and small ‘steps’ up a patients Starling curve. As a result the patient is more likely to receive fluid based on exact need.
Stroke Volume Optimisation with a less precise technology may require the clinician to administer larger (500 mL) fluid boluses and therefore take larger ‘steps’ up a patients Starling curve. As a result the patient is more likely to receive more fluid than they need.
- Singer, M., J. Clarke, and E.D. Bennett, Continuous hemodynamic monitoring by esophageal Doppler. Crit Care Med, 1989. 17(5): p. 447-52.