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Stroke Volume Variation Calculator

Enter the maximum and minimum stroke volumes to find the variation.

How it is calculated

The tool takes the largest and smallest stroke volume (SV) seen during the ventilator cycle, both in mL, and works out the spread as a share of their midpoint:

mean SV = (SVmax + SVmin) ÷ 2
SVV = (SVmax − SVmin) ÷ mean SV × 100

The mean is the average of the two extremes, not the average of every beat. Results are shown to one decimal as a percentage, and the mean SV to two decimals in mL. The result is only produced when both values are above zero, SVmax is not smaller than SVmin and SVmax is at most 500 mL; otherwise nothing is returned. Equal values give 0.0%. Values must use a decimal point.

Worked example

Suppose the monitor reports a highest stroke volume of 70 mL and a lowest of 58 mL over one breathing cycle. The mean is (70 + 58) ÷ 2 = 64 mL, shown as 64.00 mL. The spread is 70 − 58 = 12 mL. Dividing gives 12 ÷ 64 = 0.1875, and multiplying by 100 gives 18.75, which the tool rounds to 18.8%.

Try this example →

Common mistakes

  • Typing the minimum in the maximum box. If SVmax is smaller than SVmin the tool returns no result, so check the order.
  • Entering stroke volume index (mL/m²) for one value and plain stroke volume (mL) for the other. Both values must be in the same unit.
  • Using values from different breathing cycles, or from a spontaneously breathing patient. The formula assumes the extremes come from one ventilator cycle.
  • Dividing by SVmax instead of the mean. The denominator here is the midpoint of the two values, which gives a different percentage.
  • Entering a minimum of 0, or a maximum above 500 mL, because the monitor dropped out or the unit was wrong. The tool shows no result for these, so recheck the reading instead of forcing a value.

Sources

About this calculator

Stroke volume variation (SVV) measures how much a patient's stroke volume swings with each breath of positive-pressure mechanical ventilation, calculated as (SVmax − SVmin) ÷ SVmean over a respiratory cycle, typically expressed as a percentage. It works because in a fluid-responsive patient, the swings in intrathoracic pressure from ventilation cause larger cyclic changes in venous return and stroke volume — an SVV above roughly 10-13% suggests the heart is on the steep part of the Frank-Starling curve and would likely benefit from a fluid bolus, while a low SVV suggests the patient is already adequately filled.

This calculator takes the maximum and minimum stroke volumes recorded over a ventilator cycle — typically from an arterial pulse contour monitor — and returns the SVV percentage. Anesthesiologists managing goal-directed fluid therapy in the OR, and intensivists titrating fluids in mechanically ventilated ICU patients use it as a dynamic predictor of fluid responsiveness, generally more reliable in this setting than static measures like central venous pressure.

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