Arterial Blood Gas
Arterial Blood Gas
Again, look at the chart. Alkalosis is present (increased pH) with the HCO3 increased, reflecting a primary metabolic problem. Treatment of this patient might include the administration of I. V. fluids and measures to reduce the excess base. ? Copyright 2004 Orlando Regional Healthcare, Education & Development Page 11 Arterial Blood Gas Interpretation Compensation Thus far we have looked at simple arterial blood gas values without any evidence of compensation occurring. Now see what happens when an acid-base imbalance exists over a period of time.
When a patient develops an acid-base imbalance, the body attempts to compensate. Remember that the lungs and the kidneys are the primary buffer response systems in the body. The body tries to overcome either a respiratory or metabolic dysfunction in an attempt to return the pH into the normal range. A patient can be uncompensated, partially compensated, or fully compensated. When an acidbase disorder is either uncompensated or partially compensated, the pH remains outside the normal range.
In fully compensated states, the pH has returned to within the normal range, although the other values may still be abnormal. Be aware that neither system has the ability to overcompensate. In our first two examples, the patients were uncompensated. In both cases, the pH was outside of the normal range, the primary source of the acid-base imbalance was readily identified, but the compensatory buffering system values remained in the normal range. Now let’s look at arterial blood gas results when there is evidence of partial compensation.
In order to look for evidence of partial compensation, review the following three steps: 1. Assess the pH. This step remains the same and allows us to determine if an acidotic or alkalotic state exists. 2. Assess the PaCO2. In an uncompensated state, we have already seen that the pH and PaCO2 move in opposite directions when indicating that the primary problem is respiratory. But what if the pH and PaCO2 are moving in the same direction? That is not what we would expect to see happen. We would then conclude that the primary problem was metabolic.
In this case, the decreasing PaCO2 indicates that the lungs, acting as a buffer response, are attempting to correct the pH back into its normal range by decreasing the PaCO2 (“blowing off the excess CO2”). If evidence of compensation is present, but the pH has not yet been corrected to within its normal range, this would be described as a metabolic disorder with a partial respiratory compensation. 3. Assess the HCO3. In our original uncompensated examples, the pH and HCO3 move in the same direction, indicating that the primary problem was metabolic.
But what if our results show the pH and HCO3 moving in opposite directions? That is not what we would expect to see. We would conclude that the primary acid-base disorder is respiratory, and that the kidneys, again acting as a buffer response system, are compensating by retaining HCO3, ultimately attempting to return the pH back towards the normal range. The following tables (on the next page) demonstrate the relationships between the pH, PaCO2 and HCO3 in partially and fully compensated states. ? Copyright 2004 Orlando Regional Healthcare, Education & Development