This week we review a recent report on the differences between pulse oximeter Sp02 and arterial Sa02. Are there patient specific factors that may result in inaccuracies of measurement? What single ventricular factors may also result in more significant inaccuracies and how should these data be used at the bedside when assessing a child who is cyanosed? We speak with Dr. Cara Pritchett, critical care fellow at Lurie Children's Hospital - Northwestern University about a recent work she co-authored on this important and practical topic. DOI: https://doi.org/10.1016/j.jscai.2022.100394