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Cardiac Index Measured Using the Fick Principle Versus Thermodilution in Children Following Orthotopic Heart
Elyssa Cohen1, Conor O'Halloran2, Nicholas Pilli2
1Ann & Robert H. Lurie Children's Hospital of Chicago, Chicago, IL, USA. elycohen@luriechildrens.org.
Pediatric Cardiology
|June 26, 2026
Summary
The Fick method underestimates cardiac dysfunction and pulmonary hypertension after pediatric heart transplantation compared to thermodilution. These discrepancies persist for at least one year post-transplant, impacting graft function assessment.
Area of Science:
- Cardiology
- Pediatric Transplantation
- Hemodynamics
Background:
- Cardiac index (CI) and pulmonary vascular resistance (PVR) are crucial for assessing graft function post-orthotopic heart transplantation (OHT).
- Thermodilution (TD) is the gold standard, but the Fick method with LaFarge VO2 estimation is commonly used in clinical practice.
- Accurate hemodynamic monitoring is vital for managing pediatric heart transplant recipients.
Purpose of the Study:
- To compare the agreement between Fick and thermodilution methods for measuring CI and PVR in pediatric OHT patients.
- To determine if the difference between Fick and TD measurements changes over time post-transplantation.
- To evaluate the clinical implications of using the Fick method for hemodynamic assessment in this population.
Main Methods:
- Prospective observational cohort study of pediatric patients (5-18 years) undergoing OHT.
- Serial pair-wise comparisons of CI measured by Fick (LaFarge VO2) and TD.
- PVR calculated using both Fick CI and TD CI.
- Statistical analysis included descriptive statistics, multivariable models, linear mixed-effects models, and intra-class correlation (ICC).
Main Results:
- Significant discrepancies were observed: 48% of cases showed normal CI by Fick but abnormal by TD; 27% showed normal PVR by Fick but abnormal by TD.
- Low agreement between Fick and TDCI was indicated by an ICC of 0.13.
- The absolute difference between Fick and TD measurements did not significantly change over time post-OHT or with factors like VAD use or milrinone.
- TDCI did not significantly change over time since OHT when controlling for patient-level differences.
Conclusions:
- There is poor agreement between the estimated Fick method and thermodilution for determining CI and PVR after pediatric heart transplantation.
- Relying solely on the Fick method may lead to underestimation of cardiac dysfunction and pulmonary hypertension.
- These methodologic differences persist for at least the first year post-transplant, potentially affecting patient management and graft assessment.
