OXYGEN

How much oxygen is delivered to the tissues per minute?

• The delivery of oxygen to the tissues per minute is calculated from: DO2 = [1.39 x Hb x SaO₂ + (0.003 x PaO₂)] x Q

The following is the single most commonly quoted equation in critical care, and it’s worth remembering:

DO2 = [1.39 x Hb x SaO₂ + (0.003 x PaO₂)] x Q

The Delivery of oxygen (DO₂) to the tissues is determined by:

The amount of oxygen in the blood: the oxygen binding capacity of haemoglobin x the concentration of haemoglobin x the saturation of haemoglobin + the amount of dissolved oxygen all Multiplied by the Cardiac Output (Q).

The cardiac output is determined by preload, afterload and contractility.

The hemoglobin concentration  is determined by production, destruction and loss.

The SaO₂ (the saturation of haemoglobin at arterial level with oxygen - as opposed to the SpO₂ which is measured by pulse oximetery) is determined by:

The oxygen saturation curve: which equates PaO₂ (arterial oxygen tension) against SaO₂.

So if a patient has a hemoglobin of 15g/l, a cardiac output of 5L, a PaO2 of 100 and a SaO₂ of 100%, what is his oxygen delivery?

DO2 = [1.39 x 15 x 100 + (0.003 x PaO₂)] x Q = 1000 ml

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