Hyperoxia Reduces Oxygen Consumption in Children with Pulmonary Hypertension
High inspired oxygen concentration (FiO2 > 0.85) is administered to test pulmonary vascular reactivity in children with pulmonary hypertension (PH). It is difficult to measure oxygen consumption (VO2) if the subject is breathing a hyperoxic gas mixture so the assumption is made that baseline VO2 does not change. We hypothesized that hyperoxia changes VO2. We sought to compare the VO2 measured by a thermodilution catheter in room air and hyperoxia. A retrospective review of the hemodynamic data obtained in children with PH who underwent cardiac catheterization was conducted between 2009 and 2014. Cardiac index (CI) was measured by a thermodilution catheter in room air and hyperoxia. VO2 was calculated using the equation CI = VO2/arterial–venous oxygen content difference. Data were available in 24 subjects (males = 10), with median age 8.3 years (0.8–17.6 years), weight 23.3 kg (7.5–95 kg), and body surface area 0.9 m2 (0.4–2.0 m2). In hyperoxia compared with room air, we measured decreased VO2 (154 ± 38 to 136 ± 34 ml/min/m2, p = 0.007), heart rate (91 \(\pm\) 20 to 83 \(\pm\) 21 beats/minute, p=0.005), mean pulmonary artery pressure (41 \(\pm\) 16 to 35 \(\pm\) 14 mmHg, p=0.024), CI (3.6 \(\pm\) 0.8 to 3.3 \(\pm\) 0.9 L/min/m2, p = 0.03), pulmonary vascular resistance (9 \(\pm\) 6 to 7 \(\pm\) 3 WU m2, p = 0.029), increased mean aortic (61 \(\pm\) 11 to 67 \(\pm\) 11 mmHg, p = 0.005), pulmonary artery wedge pressures (11 \(\pm\) 8 to 13 \(\pm\) 9 mmHg, p = 0.006), and systemic vascular resistance (12 \(\pm\) 6 to 20 \(\pm\) 7 WU m2, p=0.001). Hyperoxia decreased VO2 and CI and caused pulmonary vasodilation and systemic vasoconstriction in children with PH. The assumption that VO2 remains unchanged in hyperoxia may be incorrect and, if the Fick equation is used, may lead to an overestimation of pulmonary blood flow and underestimation of PVRI.
KeywordsPulmonary hypertension Oxygen consumption Cardiac catheterization Pulmonary vasoreactivity Hyperoxia Thermodilution
Dr. Adatia’s research was funded by a Women and Children’s Health Research Institute and Stollery Children’s Hospital Foundation Grant. A Deloitte Clinical Research Fellowship and Stollery Children’s Hospital Foundation Academic Fellowship supported Dr. Long Guo’s salary.
Compliance with Ethical Standards
Conflict of interest
All of the authors (Long Guo, Prashant Bobhate, Shine Kumar, Karunakar Vadlamudi, Tarek Kaddoura, Mohamed Elgendi, Paula Holinski, James Y Coe, Jennifer Rutledge, Ian Adatia) declare that they have no conflicts of interest related to the material or subject of this manuscript.
The study was performed in accordance with the ethical standards of and with the approval of the University of Alberta Research Ethics Committee for research involving human subjects, who waived the need for individual consent because it was a retrospective study.