Single injection thermodilution. A flow-corrected method

Area of Science:

• Cardiovascular Physiology
• Medical Engineering
• Critical Care Medicine

Background:

• Thermodilution technique for cardiac output measurement assumes constant blood flow.
• Controlled ventilation can cause flow modulations, leading to significant errors in cardiac output estimation.
• Existing methods lack accuracy in dynamic physiological states.

Purpose of the Study:

• To develop and validate a modified Stewart-Hamilton equation for accurate cardiac output measurement.
• To correct for errors introduced by ventilation-induced blood flow variations.
• To improve the reliability of thermodilution cardiac output estimates in mechanically ventilated patients.

Main Methods:

• A flow-corrected equation was developed, incorporating relative blood flow changes.
• Relative flow was calculated using pulmonary artery pressure and pulse contour analysis.
• Measurements were performed in 16 patients undergoing coronary artery bypass surgery, comparing catheter tip transducer and fluid-filled systems.
• Cardiac output was referenced against four uncorrected thermodilution estimates.

Main Results:

• Flow correction significantly reduced variability in cardiac output estimates from 10.6% to 5.0% in Group A (P < 0.0001).
• Limits of agreement for cardiac output narrowed from +/- 1.06 L/min to +/- 0.5 L/min post-correction.
• Adequate pressure waveform quality for correction was achieved with catheter tip transducers, but not consistently with fluid-filled systems.

Conclusions:

• A single thermodilution cardiac output estimate using the flow-corrected equation is clinically feasible.
• This method requires a more complex computation and an additional pressure measurement, often already available.
• The technique offers potential for considerable reduction in patient fluid load.