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Zorluk: OrtaNephrology

A 24-year-old man with a history of type 1 diabetes mellitus is evaluated in the intensive care unit. He was admitted 12 hours ago for the management of diabetic ketoacidosis. Initial therapy included a continuous intravenous regular insulin infusion and aggressive volume resuscitation with a total of 6 liters of 0.9% sodium chloride. He is now alert and reports feeling much better. Vital signs are temperature 37.0°C (98.6°F), blood pressure 118/76 mm Hg, heart rate 88/min, and respiratory rate 20/min.

Laboratory results are as follows:
Serum sodium: 142 mEq/L
Serum potassium: 4.1 mEq/L
Serum chloride: 112 mEq/L
Serum bicarbonate: 10 mEq/L
Blood glucose: 190 mg/dL

Arterial blood gas on room air:
pH: 7.26
PaCO2: 23 mm Hg
PaO2: 95 mm Hg

Which of the following best describes this patient's current acid-base status?

  1. High anion gap metabolic acidosis and concurrent normal anion gap metabolic acidosisCevap
  2. B
    Isolated high anion gap metabolic acidosis with appropriate respiratory compensation
  3. C
    Isolated normal anion gap metabolic acidosis with appropriate respiratory compensation
  4. D
    High anion gap metabolic acidosis and concurrent respiratory alkalosis
  5. E
    High anion gap metabolic acidosis and concurrent metabolic alkalosis

Cevap

The patient has a mixed high anion gap metabolic acidosis and a concurrent normal anion gap metabolic acidosis.
This patient's arterial blood gas and electrolyte panel reveal a primary metabolic acidosis (pH 7.26, HCO3−HCO_3^- 10 mEq/L). The anion gap is calculated as 142−(112+10)=20142 - (112 + 10) = 20, indicating a high anion gap metabolic acidosis (HAGMA) due to his presenting diabetic ketoacidosis. Respiratory compensation is appropriate, as Winter's formula (1.5×10+8=231.5 \times 10 + 8 = 23) perfectly predicts his actual PaCO2PaCO_2 of 23 mm Hg. However, comprehensively evaluating a patient with a HAGMA requires a delta-delta calculation to rule out hidden metabolic disorders. The delta anion gap is 20−12=820 - 12 = 8, and the delta bicarbonate is 24−10=1424 - 10 = 14. The delta ratio (814\frac{8}{14}) is approximately 0.57. A delta ratio less than 0.8 indicates that the bicarbonate level has decreased significantly more than the anion gap has increased, which mathematically proves that a concurrent normal anion gap metabolic acidosis (NAGMA) is present. In patients treated for DKA, aggressive fluid resuscitation with 0.9% sodium chloride (which has a high chloride content) routinely causes a superimposed hyperchloremic NAGMA.

Adım Adım Çözüm

1
Identify the primary acid-base disorder by evaluating the pH and serum bicarbonate.
The pH is 7.26 (acidemia) and HCO3−HCO_3^- is 10 mEq/L, indicating a primary metabolic acidosis.
A pH < 7.35 defines acidemia, and a concurrently low bicarbonate level confirms the metabolic etiology.
2
Calculate the anion gap (AG) to determine the type of metabolic acidosis.
AG=Na+−(Cl−+HCO3−)=142−(112+10)=20AG = Na^+ - (Cl^- + HCO_3^-) = 142 - (112 + 10) = 20. The AG is elevated (normal is typically 12±212 \pm 2).
An elevated anion gap identifies the presence of a high anion gap metabolic acidosis (HAGMA), which in this patient is secondary to resolving diabetic ketoacidosis.
3
Assess for appropriate respiratory compensation using Winter's formula.
Expected PaCO2=1.5×10+8±2=23±2PaCO_2 = 1.5 \times 10 + 8 \pm 2 = 23 \pm 2 mm Hg. The actual PaCO2PaCO_2 is 23 mm Hg, which falls exactly within the expected range.
If the actual PaCO2PaCO_2 matches the expected value calculated by Winter's formula, there is no concurrent primary respiratory acid-base disorder.
4
Calculate the delta ratio to evaluate for a hidden, concurrent metabolic disorder.
ΔAG=20−12=8\Delta AG = 20 - 12 = 8. ΔHCO3−=24−10=14\Delta HCO_3^- = 24 - 10 = 14. ΔRatio=814≈0.57\Delta Ratio = \frac{8}{14} \approx 0.57.
In a pure HAGMA, the rise in AG should roughly equal the drop in bicarbonate (ratio ~1.0). A ratio < 0.8 means bicarbonate has dropped more than expected, indicating an additional normal anion gap metabolic acidosis (hyperchloremia from the massive 0.9% NaCl resuscitation).

Anahtar Kavram

Identifying a mixed high anion gap and normal anion gap metabolic acidosis using the delta-delta gap ratio.
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Nephrology

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