A simplified echocardiographic formula to estimate cardiac index in the intensive care unit

Area of Science:

• Critical Care Medicine
• Cardiovascular Imaging
• Hemodynamics

Background:

• Cardiac index (CI) measurement is vital for hemodynamic assessment in critically ill intensive care unit (ICU) patients.
• The established trans-thoracic echocardiography (TTE) method for CI estimation relies on left ventricular outflow tract (LVOT) Doppler, requiring LVOT cross-sectional area (CSA) measurement.
• Assessing LVOT-CSA in the ICU presents practical challenges, limiting the utility of traditional TTE methods.

Purpose of the Study:

• To validate a simplified, non-invasive formula for estimating cardiac index (CI) in ICU patients.
• The formula leverages only TTE LVOT-velocity time integral (VTI) and heart rate (HR), eliminating the need for LVOT-CSA measurement.

Main Methods:

• Prospective enrollment of 50 consecutive ICU patients requiring pulmonary artery catheterization (PAC).
• Cardiac index (CI) was measured using both PAC (reference) and TTE.
• TTE-derived CI was calculated using both the traditional formula (including LVOT-CSA) and the new simplified formula (LVOT-VTI and HR only).

Main Results:

• The simplified TTE formula demonstrated a strong correlation with PAC-derived CI (r=0.81).
• This correlation was significantly stronger than that of the traditional TTE formula (r=0.70; p<0.05).
• Both TTE methods showed acceptable agreement with PAC, with the simplified formula exhibiting a bias of +0.19 ± 0.48 L/min/m².

Conclusions:

• A simplified TTE-based formula using LVOT-VTI and HR is a validated and practical approach for non-invasive CI estimation in ICU patients.
• This method overcomes the limitations of traditional TTE CI assessment by omitting LVOT-CSA measurement.