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Zorluk: KolayNephrology

An 18-year-old female gymnast is brought to the university health clinic by her roommate. She has been vomiting persistently for the past four days. The roommate mentions she has observed similar episodes in the past, though not this severe. Physical examination shows dry mucous membranes, poor skin turgor, and a pulse of 112/min.

Laboratory studies show the following:
- Na+Na^+: 139 mEq/L
- K+K^+: 2.9 mEq/L
- Cl−Cl^-: 94 mEq/L
- HCO3−HCO_3^-: 36 mEq/L

Arterial blood gas analysis on room air reveals:
- pH: 7.52
- pCO2pCO_2: 48 mm Hg
- pO2pO_2: 94 mm Hg

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

  1. Primary metabolic alkalosis with appropriate respiratory compensationCevap
  2. B
    Primary metabolic alkalosis with a superimposed primary respiratory acidosis
  3. C
    Primary metabolic alkalosis with a superimposed primary respiratory alkalosis
  4. D
    Primary respiratory acidosis with compensatory metabolic alkalosis
  5. E
    Primary respiratory alkalosis with compensatory metabolic acidosis

Cevap

Primary metabolic alkalosis with appropriate respiratory compensation
This patient has a pH of 7.52, indicating an alkalemia. Her significantly elevated HCO3−HCO_3^- of 36 mEq/L establishes that the primary disorder is a metabolic alkalosis, which is classically seen with severe vomiting (due to loss of gastric hydrochloric acid and volume contraction). To determine if a mixed disorder is present, the expected respiratory compensation must be calculated. The lungs compensate for metabolic alkalosis via hypoventilation, which increases the pCO2pCO_2. The formula for expected compensation is: Expected pCO2=40+[0.7×(measured HCO3−−24)]±2pCO_2 = 40 + [0.7 \times (measured\ HCO_3^- - 24)] \pm 2. For this patient, the expected pCO2=40+[0.7×(36−24)]=40+8.4=48.4±2pCO_2 = 40 + [0.7 \times (36 - 24)] = 40 + 8.4 = 48.4 \pm 2 mm Hg (range 46.4 to 50.4 mm Hg). The patient's actual measured pCO2pCO_2 of 48 mm Hg falls perfectly within this range, indicating an appropriate physiological respiratory compensation with no superimposed secondary acid-base disorder.

Adım Adım Çözüm

1
Evaluate the pH to determine the overall acid-base direction.
The pH is 7.52, indicating an alkalemia (pH > 7.45).
The primary disorder must align with the direction of the pH deviation.
2
Examine the pCO2pCO_2 and HCO3−HCO_3^- to identify the primary etiology.
The HCO3−HCO_3^- is significantly elevated at 36 mEq/L, which drives the alkalemia.
Elevated bicarbonate in the setting of alkalemia defines a primary metabolic alkalosis. This is consistent with the patient's history of vomiting, which causes loss of gastric acid (H+H^+) and volume contraction.
3
Calculate the expected respiratory compensation.
Expected pCO2=40+[0.7×(36−24)]=40+[0.7×12]=40+8.4=48.4pCO_2 = 40 + [0.7 \times (36 - 24)] = 40 + [0.7 \times 12] = 40 + 8.4 = 48.4 mm Hg. The normal tolerance range is typically ±2\pm 2 mm Hg (46.4 - 50.4 mm Hg).
The lungs compensate for metabolic alkalosis by hypoventilating to retain CO2CO_2. The formula 0.7×ΔHCO3−0.7 \times \Delta HCO_3^- determines if the respiratory response is adequate.
4
Compare the measured pCO2pCO_2 to the expected range.
The patient's actual pCO2pCO_2 is 48 mm Hg, which is within the expected range.
Because the actual pCO2pCO_2 matches the expected compensation, there is no superimposed secondary acid-base disorder.

Anahtar Kavram

Metabolic alkalosis respiratory compensation calculation
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Nephrology

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