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Zorluk: OrtaNephrology

A 56-year-old man is brought to the emergency department by paramedics after being found unresponsive in an alley. The paramedics administered intravenous naloxone en route, which resulted in a transient increase in his respiratory rate, but he remains obtunded upon arrival. The patient is unhoused and has a history of severe alcohol use disorder. His temperature is 36.1°C (97.0°F), blood pressure is 105/65 mm Hg, pulse is 92/min, and respirations are 8/min and shallow. Pulse oximetry shows 88% on room air.

Laboratory studies show the following:
Serum sodium: 142 mEq/L
Serum potassium: 4.8 mEq/L
Serum chloride: 100 mEq/L
Serum bicarbonate: 12 mEq/L
Blood urea nitrogen: 32 mg/dL
Serum creatinine: 1.7 mg/dL

Arterial blood gas analysis on room air:
pH: 7.18
pCO2pCO_2: 50 mm Hg
pO2pO_2: 60 mm Hg

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

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

Cevap

High anion gap metabolic acidosis and concurrent respiratory acidosis
The patient's laboratory results reveal an elevated anion gap of 30 mEq/L (142 - [100 + 12]), which establishes a primary high anion gap metabolic acidosis (HAGMA), likely due to a toxic alcohol ingestion or lactic acidosis. To determine if there is a secondary acid-base disorder, Winter's formula must be applied to calculate the expected respiratory compensation: expected pCO2=(1.5×[HCO3−])+8±2pCO_2 = (1.5 \times [HCO_3^-]) + 8 \pm 2. For this patient, the expected pCO2pCO_2 is (1.5×12)+8=26±2(1.5 \times 12) + 8 = 26 \pm 2 mm Hg. The actual pCO2pCO_2 of 50 mm Hg is significantly higher than the expected range (24-28 mm Hg). This indicates inadequate alveolar ventilation resulting in CO2 retention, thereby diagnosing a concurrent primary respiratory acidosis. This is clinically consistent with the patient's shallow respirations and low respiratory rate, likely due to central nervous system depression from an unknown intoxicant.

Adım Adım Çözüm

1
Calculate the anion gap to identify the primary metabolic disturbance.
Anion gap = 142−(100+12)=30142 - (100 + 12) = 30 mEq/L.
An 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 for the metabolic acidosis.
Expected pCO2=1.5×[HCO3−]+8±2=1.5×12+8±2=26±2pCO_2 = 1.5 \times [HCO_3^-] + 8 \pm 2 = 1.5 \times 12 + 8 \pm 2 = 26 \pm 2 mm Hg.
This establishes the target range of pCO2pCO_2 (24 to 28 mm Hg) that would be expected if the patient's respiratory system were appropriately compensating.
3
Compare the actual measured pCO2pCO_2 to the expected pCO2pCO_2 to identify any secondary acid-base disorder.
The actual pCO2pCO_2 is 50 mm Hg, which is significantly higher than the expected maximum of 28 mm Hg.
A pCO2pCO_2 higher than the expected compensated range indicates inadequate alveolar ventilation, signifying a concurrent primary respiratory acidosis. This aligns clinically with the patient's hypoventilation due to suspected intoxication.

Anahtar Kavram

Diagnosis of mixed acid-base disorders requires calculating the anion gap to identify a primary metabolic acidosis, followed by applying Winter's formula (pCO2=1.5×[HCO3−]+8±2pCO_2 = 1.5 \times [HCO_3^-] + 8 \pm 2) to determine if the respiratory compensation is appropriate, insufficient (indicating concurrent respiratory acidosis), or excessive (indicating concurrent respiratory alkalosis).
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Nephrology

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