End-tidal carbon dioxide during extremely low cardiac output

Area of Science:

• Cardiovascular Physiology
• Respiratory Physiology
• Critical Care Medicine

Background:

• Expired CO2 concentration is linked to cardiac output, but cardiac output control has been limited in previous studies.
• The partial pressure of end-tidal CO2 (PETCO2) during critically low cardiac output remains under-investigated.
• Understanding this relationship is crucial for managing patients with compromised circulatory function.

Purpose of the Study:

• To measure PETCO2 under precisely controlled, very low blood flow rates.
• To investigate the correlation between PETCO2 and cardiac output with controlled minute ventilation.
• To establish a predictive model for PETCO2 based on cardiac index.

Main Methods:

• Ten swine underwent anesthesia, intubation, and mechanical ventilation.
• Ventricular assist devices were used to meticulously control cardiac output.
• Minute ventilation was maintained constant, with continuous recording of cardiac output, PETCO2, and hemodynamic pressures.

Main Results:

• Cardiac index varied widely, with a significant portion of measurements at very low levels (<1,313 mL/min/m2).
• A strong, statistically significant correlation was found between PETCO2 and cardiac index (P < .0001).
• The linear regression equation PETCO2 = 4.98 + 0.012 [cardiac index] explained 82% of the variance (r2 = .82).

Conclusions:

• PETCO2 demonstrates a robust correlation with cardiac index across a broad spectrum of blood flow rates.
• This relationship holds true even under conditions of extremely low cardiac output.
• PETCO2 can serve as a valuable, non-invasive monitor of cardiac output in mechanically ventilated patients.