Cardiac output and cardiac index
Cardiac output (CO) and cardiac index (CI) are important hemodynamic parameters characterizing cardiac function and reflecting body metabolism.
Cardiac output (CO) and cardiac index (CI) are used in the evaluation of patients with heart disease and critically ill patients as well as patients under general anesthesia 1.
Cardiac output can be used for the quantification of cardiac shunts and the calculation of pulmonary resistance 1.
There are many ways to measure cardiac output invasive and noninvasive.
A simple method is to derive cardiac output from the product of heart rate (HR) and the stroke volume (SV):
CO [L/min] = HR x SV
The cardiac index describes the cardiac output corrected for the body surface area (BSA).
CI [L/min/m2] = CO/BSA
Non-invasive imaging-based methods include the following 1:
Cardiac output can be derived from the heart rate and flow volume calculated by the velocity-time integral (VTI) and cross-sectional area (CSA) of the valve:
CO [L/min] = HR x VTI x CSA
Cardiac output can be obtained by measuring flow volume by means of velocity-encoded phase-contrast imaging multiplied with the heart rate (HR). Net volume or stroke volume can then be calculated from the difference of antegrade and retrograde volumes, which are derived from mean velocity and the cross-sectional area of the vessel 1,2:
CO [L/min] = HR [bpm] x (antegrade – retrograde volume [mL] /1000)
For accurate measurements, Venc should be adjusted to slightly above the true peak velocity 1,2.
Other non-invasive methods include pulse pressure methods, ultrasonic cardiac output monitor and impedance cardiography 1,3. Invasive methods include Fick’s principle thermodilution and dye dilution methods.
Normal values for cardiac output obviously depend on height, weight and age. Normal cardiac index slightly decreases with age and weight 4. They are usually given within the following ranges 1,4:
- Cardiac output (CO): 4.0-8.0 L/min/m2 and 3.1-6.4 L/min in individuals > 60 years
- Cardiac index (CI): 2.2-4.1 L/min/m2 and 2.1-3.2 L/min/m2 in individuals > 60 years
A cardiac index below 2.0 L/min/m2 might indicate cardiogenic shock in an acute setting.
- 1. Carlsson M, Andersson R, Bloch KM, Steding-Ehrenborg K, Mosén H, Stahlberg F, Ekmehag B, Arheden H. Cardiac output and cardiac index measured with cardiovascular magnetic resonance in healthy subjects, elite athletes and patients with congestive heart failure. (2012) Journal of cardiovascular magnetic resonance : official journal of the Society for Cardiovascular Magnetic Resonance. 14: 51. doi:10.1186/1532-429X-14-51 - Pubmed
- 2. Schulz-Menger J, Bluemke DA, Bremerich J, Flamm SD, Fogel MA, Friedrich MG, Kim RJ, von Knobelsdorff-Brenkenhoff F, Kramer CM, Pennell DJ, Plein S, Nagel E. Standardized image interpretation and post-processing in cardiovascular magnetic resonance - 2020 update : Society for Cardiovascular Magnetic Resonance (SCMR): Board of Trustees Task Force on Standardized Post-Processing. (2020) Journal of cardiovascular magnetic resonance : official journal of the Society for Cardiovascular Magnetic Resonance. 22 (1): 19. doi:10.1186/s12968-020-00610-6 - Pubmed
- 3. Cattermole GN, Leung PY, Ho GY, Lau PW, Chan CP, Chan SS, Smith BE, Graham CA, Rainer TH. The normal ranges of cardiovascular parameters measured using the ultrasonic cardiac output monitor. (2017) Physiological reports. doi:10.14814/phy2.13195 - Pubmed
- 4. Cioccari L, Luethi N, Glassford NJ, Bellomo R. The normal cardiac index in older healthy individuals: a scoping review. (2019) Critical care and resuscitation : journal of the Australasian Academy of Critical Care Medicine. 21 (1): 9-17. Pubmed