Sepsis affects both oxygen delivery to tissues, through cardiac and macro-and microcirculatory alterations [123] , and oxygen consumption, through effects on mitochondrial respiration [124] . Dyson et al. reported that the early fall in tissue oxygenation was associated with both macro-and microcirculatory impairment, the latter persisting despite restoration of the macrocirculation. However, by 24 h, this impairment had largely recovered, even though the animal predicted to have a poor prognosis were then manifesting clinical and biochemical signs of organ dysfunction, suggesting that cellular abnormalities were enhanced at this later stage [125] . Therefore, the utility of tissue PO 2 monitoring to highlight the local oxygen supply-demand balance, and dynamic O 2 challenge testing to assess microcirculatory function, merits further investigation.