The FALSE Statement is A: Respiratory Alkalosis CANNOT Coexist with Metabolic Acidosis
Statement A is NOT true—respiratory alkalosis can and frequently does coexist with metabolic acidosis in clinical practice. This represents a mixed acid-base disorder that is commonly encountered in critically ill patients.
Analysis of Each Statement
Statement A (FALSE): Cannot Coexist with Metabolic Acidosis
This statement is incorrect. Mixed acid-base disorders involving both respiratory alkalosis and metabolic acidosis occur regularly in clinical medicine. The evidence demonstrates that:
- Sepsis commonly produces this combination: Patients develop metabolic acidosis from lactic acidosis and unmeasured anions while simultaneously developing respiratory alkalosis from hyperventilation 1, 2
- Cirrhosis patients frequently exhibit this pattern: They show metabolic acidosis (from lactate and unmeasured anions) with coexisting respiratory alkalosis, which partially compensates for the acidosis 2, 3
- The respiratory alkalosis may partially offset the metabolic acidosis, preventing severe acidemia despite significant metabolic derangement 2
Statement B (TRUE): Caused by Hyperventilation
This is correct. Respiratory alkalosis results from alveolar hyperventilation, which decreases PaCO2 below the normal range of 4.6-6.1 kPa (34-46 mm Hg) 4, 5, 6, 7.
Statement C (TRUE): Can Coexist with Metabolic Alkalosis
This is accurate. Mixed respiratory and metabolic alkalosis can occur, though less common than other combinations 8, 9.
Statement D (TRUE): Cirrhosis and Sepsis are Possible Causes
This is well-established:
- Cirrhosis: Respiratory alkalosis is the most common acid-base disorder in chronic liver disease 3, 6
- Sepsis: A frequent cause of respiratory alkalosis due to hyperventilation 1, 6, 7
- Both conditions are documented causes in the evidence 2, 3
Statement E (TRUE): Severity of Hypocapnia Associated with Worse Prognosis
While the provided evidence doesn't directly address this specific prognostic relationship, the evidence does show that:
- Acidemia and metabolic acidosis are associated with mortality in critically ill cirrhotic patients 2
- Acid-base disturbances in general correlate with disease severity in critical illness 2
- Respiratory alkalosis severity reflects underlying disease processes that impact outcomes 10, 7
Clinical Pitfalls to Avoid
Do not assume a single acid-base disorder exists—always evaluate for mixed disorders, particularly in critically ill patients with sepsis or liver disease where respiratory alkalosis commonly coexists with metabolic acidosis 2, 8.
Do not rely solely on pH and standard base excess—these may appear near-normal despite multiple offsetting acid-base disturbances. Use comprehensive analysis including PaCO2, bicarbonate, anion gap, and lactate 2, 3.
Do not misdiagnose chronic respiratory alkalosis as metabolic acidosis—both cause low bicarbonate, but proper arterial blood gas interpretation distinguishes them 8.