Consumable oxygen

Oxygen delivery to the tissues, studied as oxygen availability, does not take account of the changes in oxyhemoglobin dissociation. Oxygen at a tension of less than 20 torr is considered relatively unavailable. This paper presents a clinical methodology for the analysis of oxyhemoglobin dissociation so that oxygen avail-ability can be mathematically modified by subtracting the calculated mixed venous content at a tension of 20 torr (consumable oxygen). Similar modification of the arterial oxygen content and oxygen utilization coefficient give more realistic indices of oxygen delivery. Examples are given to show how the use of these indices give a better understanding and quantification of the effects of changes in oxyhemoglobin dissociation characteristics on oxygen transport. The conventional estimations of oxygen avail-ability, arterial oxygen content and utilization coefficient do not change with shifts of the dissociation curve. A rightward shift of the curve gives a higher consumable oxygen, consumable arterial oxygen content, and a lower consumable oxygen coefficient, reflecting that more oxygen is available to the tissues before significant anaerobic metabolism is initiated.