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Zorluk: ZorNephrology

A 72-year-old man is brought to the emergency department from a nursing home due to altered mental status, fever, and rapid breathing for the past day. He has a history of benign prostatic hyperplasia and type 2 diabetes mellitus. His temperature is 39.1∘C39.1^\circ\text{C} (102.4∘F102.4^\circ\text{F}), blood pressure is 85/50 mm Hg85/50\text{ mm Hg}, pulse is 122/min122/\text{min}, and respiratory rate is 32/min32/\text{min}. Physical examination reveals a lethargic man with dry mucous membranes and right costovertebral angle tenderness.

Laboratory results are as follows:

TestResultReference Range
Serum sodium140 mEq/L140\text{ mEq/L}136−145 mEq/L136-145\text{ mEq/L}
Serum potassium4.1 mEq/L4.1\text{ mEq/L}3.5−5.0 mEq/L3.5-5.0\text{ mEq/L}
Serum chloride105 mEq/L105\text{ mEq/L}95−105 mEq/L95-105\text{ mEq/L}
Serum bicarbonate10 mEq/L10\text{ mEq/L}22−28 mEq/L22-28\text{ mEq/L}
Blood urea nitrogen42 mg/dL42\text{ mg/dL}7−18 mg/dL7-18\text{ mg/dL}
Serum creatinine2.1 mg/dL2.1\text{ mg/dL}0.6−1.2 mg/dL0.6-1.2\text{ mg/dL}
Arterial blood gas analysis on room air reveals:
ParameterResultReference Range
pH7.447.447.35−7.457.35-7.45
PaCO2\text{PaCO}_215 mm Hg15\text{ mm Hg}35−45 mm Hg35-45\text{ mm Hg}
PaO2\text{PaO}_288 mm Hg88\text{ mm Hg}75−105 mm Hg75-105\text{ mm Hg}

Which of the following best describes this patient's primary and concurrent acid-base disturbances?

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

Cevap

The correct answer is a primary respiratory alkalosis with a concurrent high anion gap metabolic acidosis.
The correct answer is a primary respiratory alkalosis with a concurrent high anion gap metabolic acidosis. The patient's pH is 7.447.44, which is on the alkalemic side of perfect neutral (7.407.40). Because physiologic compensation never completely normalizes the pH or overshoots the neutral point, a pH ≥7.40\ge 7.40 combined with a low PaCO2\text{PaCO}_2 (15 mm Hg15\text{ mm Hg}) indicates that respiratory alkalosis is the primary disorder. However, calculating the anion gap reveals a value of 25 mEq/L25\text{ mEq/L} (140−[105+10]140 - [105 + 10]). The presence of an elevated anion gap (>12 mEq/L> 12\text{ mEq/L}) always indicates a concurrent high anion gap metabolic acidosis (HAGMA), regardless of the pH. In this patient with urosepsis, the HAGMA is likely due to lactic acidosis from hypoperfusion, while the profound respiratory alkalosis is driven by systemic inflammation and fever stimulating the respiratory center.

Adım Adım Çözüm

1
Determine the primary acid-base disturbance by evaluating the arterial pH.
The pH is 7.447.44, which is on the alkalemic side of absolute neutral (7.407.40). Combined with a low PaCO2\text{PaCO}_2 (15 mm Hg15\text{ mm Hg}), this definitively indicates that the primary disorder is a respiratory alkalosis.
Physiologic compensation never normalizes the pH to the opposite side of 7.407.40. Therefore, a pH ≥7.40\ge 7.40 must be driven by a primary alkalosis, precluding a primary metabolic acidosis.
2
Calculate the serum anion gap to evaluate the metabolic component.
Anion Gap = Na+−(Cl−+HCO3−)=140−(105+10)=25 mEq/L\text{Na}^+ - (\text{Cl}^- + \text{HCO}_3^-) = 140 - (105 + 10) = 25\text{ mEq/L}.
An elevated anion gap (>12 mEq/L> 12\text{ mEq/L}) definitively identifies the presence of a high anion gap metabolic acidosis (HAGMA), regardless of the primary disorder or the current pH.
3
Synthesize the findings to establish the final acid-base diagnosis.
The patient has a primary respiratory alkalosis and a concurrent high anion gap metabolic acidosis.
Severe sepsis frequently causes a mixed acid-base disorder: lactic acidosis from poor tissue perfusion (HAGMA) and centrally-mediated hyperventilation from fever and endotoxemia (primary respiratory alkalosis).

Anahtar Kavram

Patients with severe sepsis can develop a mixed acid-base disorder characterized by a primary respiratory alkalosis (due to centrally-mediated hyperventilation) and a concurrent high anion gap metabolic acidosis (due to lactic acidosis). Physiologic compensation never overshoots the neutral pH of 7.40, making the pH direction crucial for identifying the primary disorder.
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Nephrology

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