Effects of oxygen inhalation on cardiac output, coronary blood flow and oxygen delivery in healthy individuals, assessed with MRI

Objectives Oxygen (O-2) is a cornerstone in the treatment of critically ill patients, and the guidelines prescribe 10-15 l of O-2/min even to those who are initially normoxic. Studies using indirect or invasive methods suggest, however, that supplemental O-2 may have negative cardiovascular effects. The aim of this study was to test the hypothesis, using noninvasive cardiac magnetic resonance imaging, that inhaled supplemental O-2 decreases cardiac output (CO) and coronary blood flow in healthy individuals. Methods Sixteen healthy individuals inhaled O-2 at 1, 8 and 15 l/min through a standard reservoir bag mask. A 1.5 T magnetic resonance imaging scanner was used to measure stroke volume, CO and coronary sinus blood flow. Left ventricular (LV) perfusion was calculated as coronary sinus blood flow/LV mass. Results The O-2 response was dose-dependent. At 15 l of O-2/min, blood partial pressure of O-2 increased from an average 11.7 to 51.0 kPa with no significant changes in blood partial pressure of CO2 or arterial blood pressure. At the same dose, LV perfusion decreased by 23% (P=0.005) and CO decreased by 10% (P=0.003) owing to a decrease in heart rate (by 9%, P<0.002), with no significant changes in stroke volume or LV dimensions. Owing to the decreased CO and LV perfusion, systemic and coronary O-2 delivery fell by 4 and 11% at 8 l of O-2/min, despite the increased blood oxygen content. Conclusion Our data indicate that O-2 administration decreases CO, LV perfusion and systemic and coronary O-2 delivery in healthy individuals. Further research should address the effects of O-2 therapy in normoxic patients. European Journal of Emergency Medicine 18: 25-30 (C) 2011 Wolters Kluwer Health vertical bar Lippincott Williams & Wilkins.