A nurse is reviewing the arterial blood gas (ABG) results of a client who the provider suspects has metabolic acidosis. Which of the following results should the nurse expect to see?
A.
HCO3 above 26 mEq/L
B.
PaCO2 above 45 mm Hg
C.
PaO2 below 70 mm Hg
D.
pH below 7.35
The correct answer and Explanation is :
The correct answer is D. pH below 7.35.
Explanation:
Metabolic acidosis occurs when there is an excess of acid in the body or a loss of bicarbonate (HCO₃⁻), leading to a decrease in the body’s pH levels. The normal pH range for the human body is between 7.35 and 7.45. A pH below 7.35 indicates acidosis. Since metabolic acidosis is a disturbance in the body’s bicarbonate buffer system, the pH falls as the concentration of bicarbonate decreases.
Breakdown of the ABG components:
- pH below 7.35: This is the hallmark of acidosis. A pH lower than 7.35 indicates that the body is in an acidic state. In metabolic acidosis, the low pH results from either a loss of bicarbonate (HCO₃⁻) or an accumulation of hydrogen ions (H⁺) in the blood due to the presence of excess acids.
- HCO₃ (Bicarbonate): In metabolic acidosis, HCO₃ is typically below 22 mEq/L (normal range is 22-26 mEq/L). This decrease signifies that there is either a loss of bicarbonate or an increase in acid that is consuming bicarbonate as a buffer.
- PaCO₂: This measures the partial pressure of carbon dioxide. In primary metabolic acidosis, PaCO₂ is usually normal or low, as the respiratory system compensates by hyperventilating (breathing rapidly) to blow off CO₂. A high PaCO₂ would suggest respiratory acidosis, not metabolic acidosis.
- PaO₂: While PaO₂ measures the oxygen level in the blood, it does not directly indicate metabolic acidosis. A low PaO₂ would indicate hypoxemia, which is unrelated to metabolic acidosis specifically.
Thus, in the case of metabolic acidosis, the key expectation is a pH below 7.35, signifying an acidic environment. Other findings like a low bicarbonate level confirm the metabolic cause.