Rapid interpretation of a patient's acid–base status involves integration of data provided by ABG, pH, and electrolyte measurements and history. After obtaining these data, a stepwise approach facilitates interpretation (Table 14-12: Sequential Approach to Acid–Base Interpretation).
- The pH status usually indicates the primary process (acidosis or alkalosis).
- If the PaCO2 and the pH change reciprocally but the magnitude of the pH and bicarbonate changes is not consistent with a simple acute respiratory disturbance, a chronic respiratory or metabolic problem (>24 hours) should be considered. (pH becomes nearly normal as the body compensates.)
- If neither an acute nor a chronic respiratory change could have resulted in the ABG measurements, then a metabolic disturbance must be present.
- Compensation in response to metabolic disturbances is prompt via changes in PaCO2, but renal compensation for respiratory disturbances is slower.
- Failure to consider the presence or absence of an increased anion gap results in an erroneous diagnosis and failure to initiate appropriate treatment. Correct assessment of the anion gap requires correction for hypoalbuminemia.