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Zorluk: ZorNephrology

A 19-year-old woman presents to the emergency department reporting persistent ringing in her ears, nausea, and feeling short of breath for the past 6 hours. She recently had an argument with her family and subsequently ingested an entire bottle of an over-the-counter analgesic. Vital signs include a temperature of 38.1°C (100.6°F), blood pressure of 116/74 mm Hg, pulse of 115/min, and respiratory rate of 28/min. She appears agitated and is taking deep, rapid breaths.

Initial laboratory testing reveals:

ParameterValue
Sodium140 mEq/L
Potassium3.8 mEq/L
Chloride104 mEq/L
Bicarbonate16 mEq/L
Blood urea nitrogen14 mg/dL
Creatinine0.8 mg/dL

Arterial blood gas (room air):

ParameterValue
pH7.52
PaCO220 mm Hg
PaO2102 mm Hg

Which of the following is the most accurate description of the acid-base abnormality in this patient?

  1. A
    High anion gap metabolic acidosis with appropriate respiratory compensation
  2. B
    Mixed non-anion gap metabolic acidosis and respiratory alkalosis
  3. Mixed high anion gap metabolic acidosis and respiratory alkalosisCevap
  4. D
    Respiratory alkalosis with appropriate metabolic compensation
  5. E
    Mixed high anion gap metabolic acidosis and metabolic alkalosis

Cevap

Mixed high anion gap metabolic acidosis and respiratory alkalosis
The correct answer identifies a mixed disorder characterized by a primary high anion gap metabolic acidosis (HAGMA) and a primary respiratory alkalosis. This is the classic presentation of acute salicylate toxicity (aspirin overdose). First, calculating the anion gap (140−104−16=20140 - 104 - 16 = 20 mEq/L) reveals a HAGMA. Even though the pH is alkaline (7.52), the presence of an elevated anion gap always indicates a primary metabolic acidosis. Second, Winter's formula (PaCO2=1.5×HCO3−+8±2PaCO_2 = 1.5 \times HCO_3^- + 8 \pm 2) predicts a compensatory PaCO2PaCO_2 between 30 and 34 mm Hg for a bicarbonate of 16 mEq/L. The patient's actual PaCO2PaCO_2 is much lower at 20 mm Hg. This excessive hyperventilation defines an independent primary respiratory alkalosis, which is driving the overall alkalemia. Finally, the delta ratio (20−1224−16=1.0\frac{20-12}{24-16} = 1.0) shows no evidence of a third metabolic disorder.

Adım Adım Çözüm

1
Identify the primary acid-base disturbance based on pH and PaCO2.
The pH is 7.52 (alkalemia) and the PaCO2 is 20 mm Hg. This low PaCO2 drives the alkalemia, confirming a primary respiratory alkalosis.
Evaluating the pH and PaCO2 determines the primary directional disturbance of the blood gas.
2
Calculate the anion gap to assess for a concurrent metabolic acidosis.
AG=Na+−(Cl−+HCO3−)=140−(104+16)=20AG = Na^+ - (Cl^- + HCO_3^-) = 140 - (104 + 16) = 20 mEq/L.
An anion gap >12> 12 mEq/L reveals a primary high anion gap metabolic acidosis, regardless of the overall pH.
3
Use Winter's formula to evaluate the expected respiratory compensation for the metabolic acidosis.
Expected PaCO2=(1.5×16)+8±2=32±2PaCO_2 = (1.5 \times 16) + 8 \pm 2 = 32 \pm 2 mm Hg. The measured PaCO2PaCO_2 is 20 mm Hg.
A measured PaCO2 significantly lower than expected by Winter's formula proves that the hyperventilation is far beyond simple compensation, confirming an independent primary respiratory alkalosis.
4
Calculate the delta ratio to rule out a third hidden disturbance.
ΔRatio=AG−1224−HCO3−=20−1224−16=88=1.0\Delta \text{Ratio} = \frac{AG - 12}{24 - HCO_3^-} = \frac{20 - 12}{24 - 16} = \frac{8}{8} = 1.0.
A delta ratio between 1.0 and 2.0 indicates an uncomplicated high anion gap metabolic acidosis, ruling out concurrent metabolic alkalosis or non-anion gap metabolic acidosis.

Anahtar Kavram

Diagnosis of mixed acid-base disorders in salicylate toxicity using the anion gap, Winter's formula, and delta ratio.
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Konular

Nephrology

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