Final answer:
Administering high concentrations of oxygen after cardiac arrest can impair oxygen delivery to tissues, cause oxidative stress, and negatively affect myocardial and organ function due to vasoconstriction and cellular dysfunctions.
Step-by-step explanation:
The danger of routinely administering high concentrations of oxygen during the post-cardiac arrest period for patients who achieve Return of Spontaneous Circulation (ROSC) is primarily impaired oxygen delivery to tissues. This is due to the potential for increased oxidative stress and vasoconstriction which can lead to decreased blood flow and thereby impair the delivery of oxygen to the tissues. Hyperoxia, the excess oxygen in the body's tissues, can further exacerbate injury to areas where the blood flow has already been compromised, such as areas affected by the initial cardiac event. It can also reduce cardiac output, increase systemic vascular resistance, and lead to a variety of cellular level dysfunctions, all of which can impact myocardial and overall organ function negatively after resuscitation.