Stroke Volume Index Calculator

How does this stroke volume index calculator work?

This health tool determines the mL of blood per square meter of body surface area for each heart beat. SVI is very easy to compute and involves the following equation:

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 from gender, age, weight and height based on the Mosteller, Boyd, Du Bois or Gehan- George formulas by using this BSA calculator.

SVI allows a direct comparison between patients with different weights and heights and is used in clinical studies and survival predictions in various cardiovascular diseases.

While stroke volume normal values are between 60 and 120 mL, SVI normal range is between 33 and 47 mL/m²/beat

The average body surface areas are:

■ adult men: 1.9 m²;

■ adult women: 1.6 m².

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)

Stroke volume index can also be obtained by dividing the cardiac index in L/min/m² to the heart rate in beats per minute but this method is not as often used.

Cardiac output can also be extracted with the Fick equation calculator based on the correlation with oxygen arterial and venous concentrations.

Example of a calculation

By taking the case of a patient with stroke volume = 76 mL and body surface area of 2.10 m². The rounded stroke volume index in this case = 36 mL/m²/beat

Stroke volume index and clinical studies

One of the studies employs the SVI as prognosis factor of myocardial systolic dysfunction patients with low-gradient normal EF severe aortic stenosis.

Low gradient (LG) severe aortic stenosis (AS) presented with preserved EF, reduced stroke volume is associated with adverse prognosis. The above study investigates the prognostic impact of SVI in a 4 group population of 405 patients.

The findings revealed that low SVI values are associated with higher mortality rates, depending on aortic stenosis severity.

Another example is that of the changes in SVI after esophagectomy upon postoperative renal function in a population of 128 patients that had their intraoperative hemodynamics monitored. Two groups based on SVI have been constructed:

■ Normal SVI (≥35 mL/m²)

■ Low SVI (<35 mL/m²)

and the renal function has been monitored through serum creatinine and GFR readings. The overall results revealed that patients with lower SVIs postoperative are at higher risk of developing acute kidney injury in the early post-op period compared to patients in the normal SVI range.

With further studies this could lead to a change in peri-operative management in renal surgery, perhaps to include methods to increase stroke volume in order to reduce AKI risks.

References

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

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

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

4) Eleid MF, Sorajja P, Michelena HI, Malouf JF, Scott CG, Pellikka PA. (2015) Survival by stroke volume index in patients with low-gradient normal EF severe aortic stenosis. Heart; 101(1):23-9.