Examkin

Soru

Zorluk: OrtaNephrology

A 22-year-old woman is brought to the emergency department by her roommate due to confusion, nausea, and ringing in her ears for the past several hours. The roommate found an empty bottle of over-the-counter pain relievers in her room. On physical examination, her temperature is 37.8°C (100.0°F), blood pressure is 110/70 mm Hg, pulse is 115/min, and respiratory rate is 28/min. She appears agitated and diaphoretic. Laboratory results are as follows:

Laboratory TestResult
Sodium140 mEq/L
Potassium4.1 mEq/L
Chloride104 mEq/L
Bicarbonate14 mEq/L
Blood urea nitrogen18 mg/dL
Creatinine0.9 mg/dL
Arterial blood gas (room air):
ParameterResult
pH7.42
pCO2pCO_222 mm Hg
pO2pO_295 mm Hg

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

  1. A
    Primary metabolic acidosis with adequate respiratory compensation
  2. B
    Mixed primary metabolic acidosis and primary respiratory acidosis
  3. C
    Primary respiratory alkalosis with adequate metabolic compensation
  4. Mixed primary metabolic acidosis and primary respiratory alkalosisCevap
  5. E
    Mixed primary metabolic acidosis, primary respiratory alkalosis, and primary metabolic alkalosis

Cevap

The patient has a mixed primary metabolic acidosis and primary respiratory alkalosis.
This patient's presentation of tinnitus, tachypnea, agitation, hyperthermia, and an empty bottle of over-the-counter pain relievers is classic for acute salicylate (aspirin) toxicity. Salicylates directly stimulate the medullary respiratory center, causing a primary respiratory alkalosis. Simultaneously, they uncouple oxidative phosphorylation, leading to the accumulation of lactic acid and ketoacids, which causes a primary high anion gap metabolic acidosis. The acid-base analysis confirms this exact mixed disorder: the anion gap is elevated at 22 mEq/L (indicating primary metabolic acidosis), and the measured pCO2pCO_2 of 22 mm Hg is lower than the expected compensatory range of 27-31 mm Hg calculated by Winter's formula (indicating a concurrent primary respiratory alkalosis). The delta-delta calculation yields an expected normal bicarbonate of 24 mEq/L, confirming that these are the only two primary acid-base disorders present.

Adım Adım Çözüm

1
Calculate the anion gap to evaluate for a high anion gap metabolic acidosis.
Anion gap = 140−(104+14)=22140 - (104 + 14) = 22 mEq/L. Since this is greater than the normal value of 12 mEq/L, a primary high anion gap metabolic acidosis is present.
An elevated anion gap definitively establishes the presence of a primary metabolic acidosis regardless of the final pH value.
2
Calculate the expected respiratory compensation for the metabolic acidosis using Winter's formula.
Expected pCO2=(1.5×14)+8±2=29±2pCO_2 = (1.5 \times 14) + 8 \pm 2 = 29 \pm 2 mm Hg. The calculated expected range is 27 to 31 mm Hg.
Comparing the measured pCO2pCO_2 to the expected pCO2pCO_2 determines if there is an additional primary respiratory disorder.
3
Compare the measured pCO2pCO_2 to the expected pCO2pCO_2 to identify any concurrent respiratory disorder.
The measured pCO2pCO_2 is 22 mm Hg, which is lower than the expected range of 27 to 31 mm Hg. This indicates a concurrent primary respiratory alkalosis.
A measured pCO2pCO_2 below the expected compensatory response means the patient is hyperventilating beyond what is driven by the metabolic acidosis.
4
Calculate the delta gap (delta-delta) to check for a third concurrent metabolic disorder.
Delta gap = 22−12=1022 - 12 = 10. Expected normal HCO3−=14+10=24HCO_3^- = 14 + 10 = 24 mEq/L. Since this exactly equals a normal baseline bicarbonate, there is no additional metabolic alkalosis or non-anion gap metabolic acidosis.
The delta-delta calculation reveals if the drop in bicarbonate is purely due to buffering the unmeasured anions, effectively ruling out a triple acid-base disorder.

Anahtar Kavram

Diagnosis of mixed acid-base disorders using the anion gap, Winter's formula, and delta-delta calculations.
Bu soruyu puanla

Konular

Nephrology

Bu konudan daha fazla soru