Circulatory shock is the inadequacy to supply mitochondria with enough oxygen to sustain aerobic energy metabolism. A novel non-invasive bedside measurement was recently introduced to monitor the mitochondrial oxygen tension in the skin (mitoPO2). As the most downstream marker of oxygen balance in the skin, mitoPO2 may provide additional information to improve shock management. However, a physiological basis for the interpretation of mitoPO2 values has not been established yet. In this paper we developed a mathematical model of skin mitoPO2 using a network of parallel microvessels, based on Krogh's cylinder model. The model contains skin blood flow velocity, heterogeneity of blood flow, hematocrit, arteriolar oxygen saturation and mitochondrial oxygen consumption as major variables. The major results of the model show that normal physiological mitoPO2 is in the range of 40-60mmHg. The relationship of mitoPO2 with skin blood flow velocity follows a hyperbolic curve, reaching a plateau at high skin blood flow velocity, suggesting that oxygen balance remains stable whilst peripheral perfusion declines. The model shows that a critical range exists where mitoPO2 rapidly deteriorates if skin perfusion further decreases. The model intuitively shows how tissue hypoxia could occur in the setting of septic shock, due to the profound impact of microcirculatory disturbance on mitoPO2, even at sustained cardiac output. MitoPO2 is the result of a complex interaction between all factors of oxygen delivery and the microcirculation. This mathematical framework can be used to interpret mitoPO2 values in shock, with the potential to enhance personalized clinical trial design.