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Zorluk: OrtaNephrology

A 19-year-old woman is brought to the emergency department by her college roommate due to confusion, nausea, and ringing in her ears that started 4 hours ago. The roommate reports that the patient was distraught after a recent argument, and an empty bottle of over-the-counter pain medication was found on her desk. Vital signs show a temperature of 37.8∘37.8^\circ C (100.0∘100.0^\circ F), blood pressure of 110/70110/70 mmHg, pulse of 115115/min, and respiratory rate of 2828/min. Physical examination reveals an oriented but lethargic patient. Lungs are clear to auscultation. Laboratory studies are obtained and show the following:

Serum sodium: 142142 mEq/L
Serum potassium: 4.04.0 mEq/L
Serum chloride: 104104 mEq/L
Serum bicarbonate: 1414 mEq/L
Blood urea nitrogen: 1818 mg/dL
Serum creatinine: 0.90.9 mg/dL

Arterial blood gas (room air):
pH: 7.427.42
pCO 2_2: 2020 mmHg
pO 2_2: 105105 mmHg

Based on the laboratory results, which of the following best describes this patient's acid-base disturbance?

  1. High anion gap metabolic acidosis and concurrent primary respiratory alkalosisCevap
  2. B
    High anion gap metabolic acidosis with appropriate respiratory compensation
  3. C
    Primary respiratory alkalosis with appropriate metabolic compensation
  4. D
    High anion gap metabolic acidosis and concurrent primary respiratory acidosis
  5. E
    Normal anion gap metabolic acidosis and concurrent primary respiratory alkalosis

Cevap

High anion gap metabolic acidosis and concurrent primary respiratory alkalosis
This patient presents with tinnitus, nausea, tachypnea, and an empty medication bottle, a classic vignette for salicylate (aspirin) toxicity. Salicylates cause a characteristic mixed acid-base disorder. First, calculate the anion gap: 142−(104+14)=24142 - (104 + 14) = 24 mEq/L. Because the gap is >12> 12 mEq/L, there is a primary high anion gap metabolic acidosis (HAGMA). Next, determine if the respiratory compensation is appropriate using Winter's formula: expected pCO 2_2 = (1.5×14)+8±2=29±2(1.5 \times 14) + 8 \pm 2 = 29 \pm 2 mmHg (range 27−3127-31 mmHg). The patient's actual pCO 2_2 is 2020 mmHg, which is significantly lower than the expected compensatory range. A pCO 2_2 that is lower than expected indicates the presence of a superimposed primary respiratory alkalosis, caused by the direct stimulatory effect of salicylates on the medullary respiratory center.

Adım Adım Çözüm

1
Calculate the serum anion gap.
Anion Gap = Na+−(Cl−+HCO3−)Na^+ - (Cl^- + HCO_3^-) = 142−(104+14)142 - (104 + 14) = 2424 mEq/L.
An elevated anion gap (> 12 mEq/L) establishes the presence of a primary high anion gap metabolic acidosis (HAGMA).
2
Apply Winter's formula to determine the expected respiratory compensation.
Expected pCO 2_2 = (1.5×HCO3−)+8±2(1.5 \times HCO_3^-) + 8 \pm 2 = (1.5×14)+8±2(1.5 \times 14) + 8 \pm 2 = 29±229 \pm 2 mmHg (range 27−3127-31 mmHg).
Winter's formula determines if the patient's respiratory response accurately compensates for the metabolic acidosis.
3
Compare the expected pCO2 to the measured pCO2.
The measured pCO 2_2 is 2020 mmHg, which is less than the expected range of 27−3127-31 mmHg.
Because the measured pCO2 is lower than the expected compensatory range, there is an excessive respiratory drive indicating an additional primary respiratory alkalosis.

Anahtar Kavram

Interpretation of mixed acid-base disorders using the anion gap and Winter's formula
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Konular

Nephrology

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