Description of the flow chart
The parameters in the flow chart are prioritized according to the order of evaluation. Many of the parameters influence each other. However, to make the flow chart practical in the clinical situation only the most clinically relevant parameters and interactions are included.
The key parameters (pO2, ctO2, p50) have the highest priority, while those on the far right have the lowest. Start with the key parameters from the top (pO2). Evaluate whether the values associated with it are acceptable, and if so, move on to the next parameter (in this case ctO2) and so forth.
If the key parameter being evaluated deviates from the expected range, check the columns to the right of that parameter. Find the parameters influencing the key parameter. One or more of these are possibly causing the deviation. By manipulating these parameters with treatment, it may be possible to optimize the key parameter.
Once the key parameter ranges have stabilized, move on to the next parameter. The arterial oxygen status cannot be regarded as fully assessed unless all three key parameters have been reviewed.
Lactate is an overall screening parameter, indicating whether hypoxia is present, and whether the treatment is improving the patient's condition.
Examples of how to read the flow chart
Example 1
Patient with low pO2: FShunt is found to be high and ventilator settings are changed to minimize the pulmonary shunt. This improves pO2. Next, ctO2 is evaluated and found also to be low.
sO2 is normal, but ctHb is low and blood transfusion is needed. Finally, p50 is evaluated and found to be low, expressing a left shift of the ODC. This is due to a metabolic alkalosis and a slightly elevated concentration of carboxyhemoglobin. To improve oxygen release to the tissues, the left shift of the ODC is also corrected.
Example 2
Low pO2: The oxygen availability is probably impaired. To the right is found a high FShunt, causing the hypoxemia. One step further to the right is the examination for pulmonary disease, which, in this situation, could reveal a low compliance and diffusion impairment in the lungs (ARDS). Increase in PEEP pressure and thereby mean airway pressure may in that situation minimize FShunt, and can thus be a better way to increase pO2 than just an increase in FO2(I).
When all the key parameters of arterial oxygen status have been considered, cLactate(P) should be evaluated. If cLactate is the first parameter to be looked at, and if it is found to be too high, the next step will be to look at the parameters in the column to the right to find the cause of the high lactate concentration.
