The Ratio Fallacy, with Special Reference to the Cardiac Index

Area of Science:

• Pediatric Cardiology
• Physiology

Background:

• Cardiac output is frequently normalized to body surface area (BSA) using the cardiac index for comparisons.
• The cardiac index may introduce significant errors when assessing cardiac output in small infants.

Purpose of the Study:

• To highlight the limitations of the cardiac index in pediatric populations.
• To propose an alternative method for evaluating cardiac output in children.

Main Methods:

• Review of existing methodologies for cardiac output assessment in pediatrics.
• Analysis of the accuracy of cardiac index versus z values for different pediatric age groups.

Main Results:

• The cardiac index demonstrates potential for large errors in small infants.
• Z values provide a more accurate and reliable assessment of cardiac output across diverse pediatric sizes.

Conclusions:

• The use of z values is recommended for evaluating cardiac output in children, particularly infants.
• Relying on the cardiac index for neonates and small infants may lead to misinterpretations of cardiovascular status.