The application of partial pressure of oxygen adjusted indirect Fick method in vasoreactivity testing by inhaling oxygen in congenital heart disease.

The influence of partial pressure of oxygen (pO2) is often overlooked during vasoreactivity testing by inhaling oxygen in congenital heart diseases (CHD). This study aims to evaluate the influence of pO2 on hemodynamic data. Patients with simple CHDs and suspected pulmonary arterial hypertension undergoing right heart catheterization including vasoreactivity testing by inhaling O2 were consecutively enrolled from June 2023 to March 2025. Patients with an arterial O2 saturation below 98% after inhaling O2 were excluded. Cardiac output was calculated using indirect Fick method, where blood O2 content (1.39 × hemoglobin × O2 saturation + 0.032 × pO2) was excluded (unadjusted) or included (adjusted) with the pO2 term. Hemodynamic data after inhaling O2 calculated by both methods were compared. An over 20% decrease in pulmonary vascular resistance with stable blood pressure was considered a positive vasoreactivity testing. During the study period, a total of 136 patients with simple CHDs were enrolled and 129 of them were diagnosed with pulmonary arterial hypertension. In vasoreactivity testing, after adjustment, pulmonary / systemic blood flow ratio decreased from 4.32 ± 5.82 to 2.51 ± 1.67, while pulmonary vascular resistance was increased from 5.62 ± 4.18 WU to 7.04 ± 4.44 WU. The response to O2 was adjusted to negative in 19 patients. The pO2-adjusted indirect Fick method incorporates the effect of dissolved O2 in hemodynamical data calculation, reducing overestimation of pulmonary / systemic blood flow ratio and underestimation of pulmonary vascular resistance in vasoreactivity testing by inhaling O2 for patients with simple CHDs.