In evaluating acid-base disorders, what is the first step?

In evaluating acid-base disorders, what is the first step?

• A. Determine primary acidosis/alkalosis by examining pH, PaCO2, and HCO3-
• B. Calculate the anion gap
• C. Check bicarbonate alone
• D. Measure lactate

Answer: (C)

Start by checking the pH to see whether the patient is acidemic or alkalemic. That tells you there is an acid-base disturbance and in which direction the imbalance lies. Once the pH abnormality is established, identify the primary disorder by examining the two main acid-base components: bicarbonate and the arterial CO2. A low bicarbonate with a normal or only slightly abnormal CO2 points to a metabolic disturbance with appropriate respiratory compensation; a high CO2 with a normal or near-normal bicarbonate points to a primary respiratory disturbance with metabolic compensation. This approach also lets you judge whether any additional disorders are present by comparing the observed values to the expected compensatory changes. In short, the first step is to determine acidemia or alkalemia from the pH, then use bicarbonate and PaCO2 to define the primary disorder and assess compensation.

Start by checking the pH to see whether the patient is acidemic or alkalemic. That tells you there is an acid-base disturbance and in which direction the imbalance lies. Once the pH abnormality is established, identify the primary disorder by examining the two main acid-base components: bicarbonate and the arterial CO2. A low bicarbonate with a normal or only slightly abnormal CO2 points to a metabolic disturbance with appropriate respiratory compensation; a high CO2 with a normal or near-normal bicarbonate points to a primary respiratory disturbance with metabolic compensation. This approach also lets you judge whether any additional disorders are present by comparing the observed values to the expected compensatory changes. In short, the first step is to determine acidemia or alkalemia from the pH, then use bicarbonate and PaCO2 to define the primary disorder and assess compensation.