A recent study by Iguchi et al (Anaesth 2020;125(2):192-200) showed that measured renal tissue oxygen tension falls under anaesthesia and may apparently be normalised by increasing arterial oxygen tension. In reality tissue oxygen is a balance between supply, demand and diffusion and is not spatially homogeneous at capillary length scales. This apparent normalisation may be falsely reassuring as such measurements reflect a macroscopic spatial average and being disproportionately influenced by regions of peri-arterial hyperoxia with other areas of tissue remaining unaffected and potentially hypoxic. Therefore, clinicians should not caution before translating the apparently beneficial effects of supraphysiological arterial oxygen levels on measured renal tissue oxygen tension into clinical practice.