Impact of Thermodilution on Indexed Pulmonary Vascular Resistance Calculations in Pediatric Pulmonary Arterial...

Accurate assessment of pulmonary vascular resistance index (PVRi) is essential for the diagnosis and management of pulmonary arterial hypertension (PAH). PVRi depends on pulmonary blood flow (Qp), which can be determined by thermodilution or the Fick principle. However, agreement between these methods in children with PAH remains poorly characterized.

We performed a retrospective single-center study of 209 cardiac catheterizations in 50 pediatric patients with WHO Group 1 PAH. Thermodilution-derived Qp was obtained in patients without significant intracardiac shunting and compared with Fick-derived Qp using reported oxygen consumption (VO₂), which was obtained by direct measurement (173 procedures, 93%) or the Seckeler equation (13 procedures, 7%). Agreement between methods was assessed using Bland-Altman analysis, and multivariable linear regression was performed to identify predictors of discrepancies in PVRi.

Thermodilution-derived PVRi was, on average, 2.0 Wood units·m² lower than Fick-derived PVRi. The discrepancy increased as PVRi increased (R² = 0.47). Differences in VO₂ estimation contributed minimally to variability in PVRi compared with differences in Qp determination. Among patients who underwent serial catheterizations, thermodilution was used consistently in only 42%, whereas 58% had variable use across procedures.

Thermodilution systematically yields lower PVRi than the Fick method in pediatric PAH, particularly in patients with higher PVRi. These findings highlight the importance of maintaining a consistent method of Qp determination during serial catheterizations to improve interpretation of longitudinal hemodynamic changes and clinical decision-making.