What is a normal cardiac index?

Normal Cardiac Index

The normal cardiac index is 2.2-4.0 L/min/m², with values below 2.2 L/min/m² indicating inadequate cardiac output and values above 4.0 L/min/m² suggesting a hyperdynamic state. 1

Standard Reference Values

Cardiac index represents cardiac output normalized to body surface area, providing a standardized measurement that accounts for differences in body size. 2 The most widely accepted normal range across major cardiovascular societies is:

• Normal range: 2.2-4.0 L/min/m² 1
• Lower limit of normal: 1.9 L/min/m² 3
• Upper limit of normal: 4.3 L/min/m² 3

The European Society of Cardiology defines normal cardiac function as maintaining a cardiac index in excess of 2.0 L/min/m² with a pulmonary capillary wedge pressure of less than 20 mmHg. 4

Gender and Age Considerations

Cardiac index is remarkably stable and not significantly influenced by gender or age in adults. 3 In a large echocardiographic study of 4,040 adults:

• Both males and females share identical cardiac index normal limits (1.9-4.3 L/min/m²) 3
• Cardiac index remains stable across age groups from 20 to >60 years 3
• While cardiac output differs between genders (males: 3.5-8.2 L/min; females: 3.3-7.3 L/min), indexing to body surface area eliminates this difference 3

Cardiovascular magnetic resonance studies confirm minimal age-related decline, showing only an 8 mL/min/m² decrease per year, with mean values ranging from 3.3 L/min/m² in the 20-29 age group to 3.0 L/min/m² in those over 60 years. 5

Clinical Thresholds for Pathology

Cardiogenic Shock

A cardiac index <2.2 L/min/m² combined with systolic blood pressure <90 mmHg and pulmonary capillary wedge pressure >15 mmHg defines cardiogenic shock. 4, 1 The American College of Cardiology specifies that cardiac index <2.0 L/min/m² with hypotension constitutes hemodynamic criteria for shock diagnosis. 4

Heart Failure

In decompensated heart failure, cardiac index is usually <2.2 L/min/m². 4 Patients with congestive heart failure and ejection fraction below 40% demonstrate mean cardiac index of 2.3 ± 0.6 L/min/m², significantly lower than healthy populations. 5

Acute Myocardial Infarction

The European Society of Cardiology recommends targeting a cardiac index >2.0 L/min/m² with filling pressure (pulmonary wedge) of at least 15 mmHg in patients with pump failure following myocardial infarction. 4

Body Habitus Considerations

Cardiac index remains stable regardless of obesity status. 3 In obese patients (BMI ≥30 kg/m²):

• Normal limits: 1.8-4.1 L/min/m² for both genders 3
• Absolute cardiac output is higher in obese patients, but cardiac index (normalized to body surface area) does not differ significantly from non-obese individuals 3
• This stability makes cardiac index superior to absolute cardiac output for defining low- and high-output states across different body sizes 3

Measurement Reliability

Cardiac index demonstrates remarkable consistency across measurement modalities when properly performed. 2 The American College of Cardiology recommends thermodilution as the standard invasive method, while Doppler echocardiography provides reliable non-invasive assessment. 2

Critical Pitfall

In patients with severe tricuspid regurgitation, thermodilution underestimates cardiac output; use the Fick method instead. 2 Additionally, cardiac index measured in older adults (>60 years) may range lower (2.1-3.2 L/min/m²) than traditionally reported, with scant data available for those over 80 years. 6

Practical Application

When cardiac index falls below 2.2 L/min/m² with evidence of hypoperfusion (decreased mentation, cold extremities, urine output <30 mL/h, lactate >2 mmol/L), immediate intervention is required. 4, 1 The threshold of 2.2 L/min/m² serves as a critical decision point for initiating inotropic support, mechanical circulatory support, or escalating hemodynamic monitoring. 4