What are the typical arterial blood gas (ABG) findings in Addison's crisis?

Arterial Blood Gas Findings in Addison's Crisis

In Addison's crisis, arterial blood gas (ABG) typically shows metabolic acidosis with hyponatremia, hyperkalemia, and often hypoglycemia.

Primary ABG Findings in Addison's Crisis

• Metabolic acidosis: Characterized by low pH (<7.35) and low bicarbonate (<22 mmol/L) due to loss of mineralocorticoid function 1
• Low serum sodium (hyponatremia): A hallmark laboratory finding in adrenal crisis 1
• High serum potassium (hyperkalemia): Due to lack of aldosterone, though rarely hypokalemia may occur in special circumstances 1, 2
• Elevated creatinine: Caused by prerenal renal failure due to severe dehydration 1
• Hypoglycemia: Particularly common in children but can occur in adults as well 1

Detailed ABG Interpretation

Acid-Base Status

• pH is typically low (<7.35) indicating acidemia 3, 4
• Bicarbonate (HCO3-) is decreased (<22 mmol/L) 3, 4
• Base excess is negative (<-1.9) confirming metabolic acidosis 3
• PaCO2 may be normal or low as respiratory compensation attempts to normalize pH 4

Electrolyte Abnormalities

• Sodium is typically low (<135 mmol/L) due to mineralocorticoid deficiency 1
• Potassium is typically elevated (>5.0 mmol/L), though this finding may be absent in up to 40% of cases 1
• Mild hypercalcemia may occasionally be present 1

Clinical Correlation

• The severity of metabolic acidosis often correlates with the severity of the adrenal crisis 1
• ECG changes may be present due to electrolyte abnormalities, particularly hyperkalemia, and can resolve with appropriate treatment 5
• Hypotension and shock may worsen the metabolic acidosis due to tissue hypoperfusion 1

Pitfalls in Interpretation

• Atypical presentations: Rarely, Addison's disease may present with hypokalemia rather than hyperkalemia, particularly if there is concurrent renal tubulopathy 2
• Mixed disorders: Patients may have mixed acid-base disorders if they have vomiting (causing metabolic alkalosis) or respiratory compensation 4, 6
• Sample timing: ABG results may vary depending on when in the course of adrenal crisis the sample was taken and what treatments have been initiated 7
• Venous vs. arterial samples: In emergency situations, venous blood gas may be obtained instead of arterial, which typically shows slightly lower pH (by 0.03-0.05) and higher pCO2 (by 4-5 mmHg) 3, 8

Management Implications

• ABG findings help guide fluid and electrolyte replacement therapy 1
• Immediate administration of hydrocortisone 100 mg IV bolus is required regardless of ABG results 1
• Rapid administration of isotonic saline (0.9%) is crucial, with initial infusion rate of approximately 1 L/hour 1
• Glucose administration may be necessary if hypoglycemia is present 1
• Serial ABGs may help monitor response to treatment 4, 6

Differential Diagnosis Based on ABG

• Metabolic acidosis with hyperkalemia may also be seen in:

  • Diabetic ketoacidosis (but typically with hyperglycemia rather than hypoglycemia) 1
  • Acute kidney injury 4
  • Lactic acidosis from shock of any cause 4

• The combination of hyponatremia, hyperkalemia, and metabolic acidosis with hypoglycemia is highly suggestive of adrenal crisis 1