Stroke Volume Index Calculator

Variables and formula

The stroke volume index represents the amount of blood in mL, per square meter of body surface area, that is mobilized with each heart beat.

This index is often used in clinical studies and in predicting survival in different cardiovascular diseases because it allows a comparison of stroke volume in patients of different, genders, ages, weights or heights.

The formula used for calculation is:

Stroke volume index = Stroke volume in mL / Body surface area in m²

Where:

■ Stroke volume = Cardiac Output / Heart rate in bpm

■ Body surface area can be estimated through Mosteller, Boyd, Du Bois or Gehan- George formulas. These can be found in the BSA calculator.

By employing the SV and cardiac output formulas the following correlations can be made:

SVI = (Stroke volume) / (Body surface area) = ((Cardiac output) / (Heart rate)) / (Body surface area) = (Cardiac output) / (Heart rate x Body surface area)

Normal stroke volume is between 60 and 120 mL per heart beat. SVI normal range is between 33 and 47 mL/m²/beat.

The average body surface area is gender dependent:

■ BSA in adult men: 1.9 m²;

■ BSA in adult women: 1.6 m².

Cardiac output can be extracted through the Fick equation which is based on the relationship between the concentration of arterial and venous oxygen.

SVI and clinical studies

SVI has been employed as prognosis factor of myocardial systolic dysfunction in a study on 405 patients diagnosed with low-gradient, normal EF, severe aortic stenosis.

In the above condition, the reduction in stroke volume is associated with adverse prognosis, especially when linked with an advanced degree of aortic stenosis.

Another study on 128 patients has looked at changes in SVI after esophagectomy upon postoperative renal function. Intraoperative hemodynamics have been monitored on the duration of the study and two groups have been constructed:

■ Normal SVI (≥35 mL/m²);

■ Low SVI (<35 mL/m²).

The study concluded that patients with low SVI values are at a higher risk of developing acute kidney injury in the early post-op period compared to patients with normal range or slight increase in SVI.

References

1. Reuter DA, Kirchner A, Felbinger TW, Weis FC, Kilger E, Lamm P, Goetz AE. Usefulness of left ventricular stroke volume variation to assess fluid responsiveness in patients with reduced cardiac function. Crit Care Med. 2003; 31(5):1399-404.

2. Marx G, Cope T, McCrossan L, Swaraj S, Cowan C, Mostafa SM, Wenstone R, Leuwer M. Assessing fluid responsiveness by stroke volume variation in mechanically ventilated patients with severe sepsis. Eur J Anaesthesiol. 2004; 21(2):132-8.

3. Sugasawa Y, Hayashida M, Yamaguchi K, Kajiyama Y, Inada E. Usefulness of stroke volume index obtained with the FloTrac/ Vigileo system for the prediction of acute kidney injury after radical esophagectomy. Ann Surg Oncol. 2013; 20(12):3992-8.