A client with diabetic ketoacidosis has pH 7.28, PaCO2 26 mm Hg, and HCO3 12 mEq/L. Using Winter's formula, complete the acid-base interpretation.
Drop-down Cloze
Choose your responses, then check the answer.
Explanation
The low pH and low bicarbonate identify primary metabolic acidosis. Winter's formula gives an expected PaCO2 of 24 to 28 mm Hg: (1.5 × 12) + 8 ± 2. The measured PaCO2 of 26 mm Hg is within that range, so respiratory compensation is appropriate and there is no evidence from these values of an additional primary respiratory disorder. Appropriate compensation does not need to normalize the pH.
Correct Answer The primary disorder is metabolic acidosis, expected PaCO2 is 24 to 28 mm Hg, and the measured value indicates appropriate respiratory compensation without a second primary respiratory disorder.
Why It Fits The bicarbonate decrease explains the acidemia, and the measured PaCO2 falls inside the calculated compensatory range.
Clinical Picture Deep rapid breathing lowers carbon dioxide in response to metabolic acid. Winter's formula distinguishes expected compensation from an additional respiratory problem.
Memory Link Low pH plus low HCO3 means metabolic acidosis; calculate the expected PaCO2 instead of guessing compensation.
NCLEX Rule A PaCO2 above the expected range suggests added respiratory acidosis; below the range suggests added respiratory alkalosis.
Why the Alternatives Fail Calling this respiratory alkalosis ignores the primary bicarbonate decrease. Calling compensation inadequate only because pH remains low ignores the calculated expected range.
Sources
12024 Hyperglycemic Crises Consensus Report
2Merck Manual: Acid-Base Disorders
32026 NCLEX-RN Test Plan
The client is awake with deep, rapid respirations. Expected PaCO2 = (1.5 × HCO3) + 8 ± 2. The nurse must identify the primary disorder and decide whether the measured PaCO2 suggests a second respiratory disorder.
Winter's formula — A calculation used in metabolic acidosis to estimate expected PaCO2: (1.5 × HCO3) + 8 ± 2 mm Hg.
Metabolic acidosis — An acid-base disorder in which a primary decrease in bicarbonate lowers blood pH.
Mixed acid-base disorder — More than one primary acid-base process, suggested when compensation falls outside the expected range.