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Zorluk: ZorNephrology

Emergency medical services transport a 6565-year-old man from a long-term care facility to the hospital due to acute-onset confusion, fever, and severe abdominal pain. His past medical history is significant for alcohol-associated cirrhosis with refractory ascites, which is managed with high-dose furosemide and spironolactone. Upon arrival, his temperature is 39.2∘39.2^\circ C (102.6∘102.6^\circ F), blood pressure is 80/5080/50 mm Hg, heart rate is 122122/min, and respiratory rate is 2828/min. Abdominal examination reveals severe distension, diffuse tenderness, and involuntary guarding. Laboratory results are as follows:

Laboratory TestResult
Sodium132132 mEq/L
Potassium3.13.1 mEq/L
Chloride8282 mEq/L
Bicarbonate1616 mEq/L
Blood urea nitrogen4545 mg/dL
Creatinine2.22.2 mg/dL
Lactate7.57.5 mmol/L
Arterial blood gas (room air):
ParameterResult
pH7.507.50
pCO2_22121 mm Hg
pO2_26868 mm Hg

Based on the clinical presentation and laboratory results, which of the following sets of acid-base disorders is present in this patient?

  1. High anion gap metabolic acidosis, metabolic alkalosis, and respiratory alkalosisCevap
  2. B
    High anion gap metabolic acidosis and respiratory alkalosis
  3. C
    High anion gap metabolic acidosis, normal anion gap metabolic acidosis, and respiratory alkalosis
  4. D
    High anion gap metabolic acidosis and metabolic alkalosis
  5. E
    Normal anion gap metabolic acidosis, metabolic alkalosis, and respiratory alkalosis

Cevap

The correct answer is the set containing a high anion gap metabolic acidosis, a metabolic alkalosis, and a respiratory alkalosis.
The patient's ABG shows an alkalemia (pH > 7.457.45) driven by hypocapnia (pCO 2_2 < 4040 mm Hg), indicating a primary respiratory alkalosis. This is clinically consistent with hyperventilation due to severe sepsis and fever. Next, calculating the anion gap (AG): AG = Na +^+ - (Cl −^- + HCO 3−_3^-) = 132−(82+16)=34132 - (82 + 16) = 34 mEq/L. Since the normal AG is 1212 mEq/L, an AG of 3434 confirms the presence of a high anion gap metabolic acidosis (HAGMA), resulting from lactic acidosis due to septic shock. Finally, to check for a third disorder, a delta-delta calculation is performed. The Δ\Delta AG is 34−12=2234 - 12 = 22. The corrected HCO 3−_3^- = measured HCO 3−_3^- + Δ\Delta AG = 16+22=3816 + 22 = 38 mEq/L. Because the corrected HCO 3−_3^- (3838 mEq/L) is significantly greater than the normal baseline (2424 mEq/L), there is a concurrent metabolic alkalosis. This is clinically explained by the patient's ongoing use of high-dose loop diuretics for his cirrhosis. Therefore, a triple acid-base disorder is present.

Adım Adım Çözüm

1
Analyze the pH to determine the primary acid-base disturbance.
The pH is 7.507.50, indicating alkalemia.
Establishing the primary disturbance helps anchor the subsequent interpretation.
2
Evaluate the pCO 2_2 and HCO 3−_3^- to identify the driver of the alkalemia.
The pCO 2_2 is markedly low at 2121 mm Hg, and the HCO 3−_3^- is low at 1616 mEq/L. The low pCO 2_2 explains the alkalemia, confirming a primary respiratory alkalosis.
Respiratory alkalosis in this patient is driven by hyperventilation secondary to sepsis and fever.
3
Calculate the anion gap (AG) to check for a metabolic acidosis.
AG = Na +^+ - (Cl −^- + HCO 3−_3^-) = 132−(82+16)=34132 - (82 + 16) = 34 mEq/L.
An AG > 1212 mEq/L indicates a high anion gap metabolic acidosis (HAGMA), driven here by lactic acidosis from septic shock.
4
Perform a delta-delta calculation to unmask any hidden third disorder.
Δ\Delta AG = 34−12=2234 - 12 = 22. Corrected HCO 3−_3^- = measured HCO 3−_3^- (1616) + Δ\Delta AG (2222) = 3838 mEq/L.
Because the corrected HCO 3−_3^- (3838 mEq/L) is significantly greater than the baseline of 2424 mEq/L, there is a concurrent metabolic alkalosis, likely secondary to loop diuretic therapy.

Anahtar Kavram

Diagnosis of triple acid-base disorders using the anion gap and delta-delta calculations.

Alternatif Yöntem

Instead of using the corrected bicarbonate formula, the delta ratio (Δ\Delta AG / Δ\Delta HCO 3−_3^-) can be used. Δ\Delta AG = 34−12=2234 - 12 = 22. Δ\Delta HCO 3−_3^- = 24−16=824 - 16 = 8. The delta ratio is 22/8=2.7522 / 8 = 2.75. A delta ratio greater than 2.02.0 confirms the presence of a concurrent metabolic alkalosis.
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