OXYGEN DELIVERY (DO2)
The goal of therapy is to correct and optimize inadequate tissue perfusion and oxygen delivery.
Oxygen delivery represents the amount or volume of oxygen transported to the tissues each
minute. Oxygen delivery is the product of cardiac output and oxygen content. Cardiac output
is the product of stroke volume and heart rate. To improve or increase cardiac output, the
heart rate and or stroke volume has to increase. Stroke volume is the amount of blood
pumped out of the heart with each beat and there are three primary determinants of stoke
volume. Stroke volume is increased in proportion to: 1) the stretch of the walls of the ventricles
during diastole (preload); 2) the strength of contraction (contractility) and 3) decreases in the
forces that oppose blood flow from the heart (afterload) (i.e. in the absence of valvular
stenosis, arterial blood pressure).
Oxygen Content (CaO2) is the amount of oxygen in arterial blood. Oxygen is either dissolved
in plasma or bound to hemoglobin. Hemoglobin is the main carrier of oxygen in the blood.
Each gram of hemoglobin has the capacity to carry 1.34 ml of O2 (20.1 mls O2 / deciliter of
blood when the hemoglobin is 15 gm/dl). Only 0.3 ml of O2/deciliter blood is dissolved in the
plasma when the PaO2 is 100 mm Hg.