Normal Cardiac Index
The normal cardiac index in adults is 2.2-4.0 L/min/m², with values below 2.2 L/min/m² indicating inadequate cardiac output and potential shock states. 1
Standard Reference Values
The American College of Cardiology establishes the normal cardiac index range as 2.2-4.0 L/min/m², which serves as the fundamental hemodynamic parameter for assessing cardiac function and differentiating shock types. 1 This standardized measurement accounts for body surface area differences, making it superior to raw cardiac output for comparing cardiac function between individuals. 2
Age-Related Considerations
Cardiac index demonstrates a modest decline with advancing age, though the clinical significance remains limited:
- In healthy adults aged 20-29 years: 3.3 ± 0.4 L/min/m² 3
- In healthy adults aged 30-39 years: 3.3 ± 0.5 L/min/m² 3
- In healthy adults aged 40-49 years: 3.1 ± 0.5 L/min/m² 3
- In healthy adults aged 50-59 years: 3.0 ± 0.4 L/min/m² 3
- In healthy adults ≥60 years: 3.0 ± 0.4 L/min/m² 3
The decline rate is approximately 3.5-8 mL/min/m² per year in some populations, though this finding is inconsistent across studies. 4 A large echocardiographic study found only 8 mL/min/m² per year decline (r² = 0.07), indicating age explains minimal variance in cardiac index. 3
Gender and Body Habitus
Cardiac index shows no clinically significant difference between males and females when properly indexed to body surface area. 5, 3 The lower and upper limits are identical for both genders: 1.9 L/min/m² and 4.3 L/min/m² respectively. 5
Obesity does not alter cardiac index values despite increasing absolute cardiac output, as the indexing to body surface area normalizes the measurement. 5 The normal range in obese patients (1.8-4.1 L/min/m²) does not differ significantly from non-obese individuals. 5
Critical Clinical Thresholds
Pathologic Values
Cardiac index <2.2 L/min/m² combined with systolic blood pressure <90 mmHg and pulmonary capillary wedge pressure >15 mmHg defines cardiogenic shock. 1 This threshold serves as a critical decision point for:
- Initiating inotropic support 1
- Considering mechanical circulatory support 1
- Escalating hemodynamic monitoring 1
Cardiac index <2.0 L/min/m² with hypotension constitutes hemodynamic criteria for shock diagnosis, regardless of etiology. 1 The European Society of Cardiology defines severe cardiac dysfunction as cardiac index <1.8 L/min/m² with central filling pressure >20 mmHg. 1
Refractory Shock
Cardiac power output <0.6 W represents the most critical threshold for identifying refractory cardiogenic shock, even more predictive than cardiac index alone. 1 This occurs when cardiac index remains <2.2 L/min/m² despite maximal doses of two vasoactive medications and treatment of the underlying cause. 1
Hemodynamic Patterns in Disease States
Cardiogenic Shock
- Cardiac index: <2.2 L/min/m² (decreased) 1
- Systemic vascular resistance: elevated (compensatory) 1
- Pulmonary capillary wedge pressure: >15 mmHg (elevated) 1
- Central venous pressure: elevated 1
Distributive Shock
- Cardiac index: normal or increased 1
- Systemic vascular resistance: decreased 1
- Pulmonary capillary wedge pressure: normal or decreased 1
Heart Failure
In decompensated heart failure, cardiac index is typically <2.2 L/min/m². 1 Patients with congestive heart failure and ejection fraction <40% demonstrate mean cardiac index of 2.3 ± 0.6 L/min/m², significantly lower than healthy controls (p <0.001). 3
Measurement Considerations
The thermodilution method via pulmonary artery catheter remains the gold standard for invasive cardiac index measurement, requiring measurements in triplicate for reliability. 2 However, severe tricuspid regurgitation causes underestimation, necessitating the Fick method instead. 2
Noninvasive echocardiographic measurement using Doppler velocity-time integral provides reliable cardiac index assessment in most clinical scenarios. 2, 5 The normal limits by echocardiography (1.9-4.3 L/min/m²) align closely with invasive measurements. 5
Common Pitfalls
Avoid using cardiac output alone without indexing to body surface area, as this fails to account for body size differences and can misclassify cardiac function. 2 A cardiac output of 4.5 L/min may be normal in a small person but inadequate in a large individual.
Do not directly compare cardiac index values obtained from different measurement techniques (CMR vs. echocardiography vs. thermodilution), as systematic differences exist between modalities despite measuring the same physiologic parameter. 6
In elderly patients >80 years, recognize that data on normal cardiac index values are extremely limited, with only one study measuring nine individuals in this age group. 4 The lower end of normal may be 2.1 L/min/m² in this population. 4