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Difficulty: MediumRheumatology and Immunology

During a routine prenatal visit at 2828 weeks gestation, a primigravid patient with a known history of systemic lupus erythematosus is evaluated. She reports new-onset exertional dyspnea and mild fatigue over the past two weeks. Her systemic lupus erythematosus has been well controlled with hydroxychloroquine for the past three years. Vital signs are within normal limits, and physical examination reveals clear lung fields bilaterally and trace dependent pedal edema.

Laboratory analysis reveals:
ParameterResult
Hemoglobin10.810.8 g/dL
Platelet count210,000210,000/mm3^3
Serum creatinine0.60.6 mg/dL
UrinalysisTrace protein, no cellular casts
An arterial blood gas obtained on room air demonstrates:
ParameterResult
pH7.447.44
pCO₂2929 mm Hg
pO₂104104 mm Hg
HCO₃⁻2020 mEq/L

Which of the following is the most appropriate next step in the management of this patient?

  1. A
    Initiate oral prednisone therapy
  2. B
    Administer intravenous furosemide
  3. Reassure the patient and continue current managementAnswer
  4. D
    Administer intravenous sodium bicarbonate
  5. E
    Prescribe oral amoxicillin-clavulanate

Answer

Reassure the patient and continue current management.
The correct approach is to reassure the patient and continue her current regimen. This patient is experiencing normal physiologic changes of pregnancy. Progesterone stimulates the medullary respiratory center, causing an increase in tidal volume and minute ventilation, which manifests as a chronic respiratory alkalosis (low pCO₂) with a compensatory metabolic acidosis (decreased HCO₃⁻). Additionally, maternal plasma volume expands more than red blood cell mass, leading to physiologic dilutional anemia. Trace pedal edema and mild exertional dyspnea are also normal as pregnancy progresses. Crucially, there is no evidence of a systemic lupus erythematosus flare; her creatinine is normal, and urinalysis shows only trace protein without cellular casts.

Step-by-Step Solution

1
Analyze the patient's symptoms and physical examination findings.
The patient has mild exertional dyspnea and trace pedal edema, which are normal, expected findings in the late second and third trimesters of pregnancy due to an expanding uterus and increased plasma volume.
To differentiate between physiologic changes of pregnancy and pathological disease processes.
2
Evaluate the laboratory and arterial blood gas results.
The patient has a mild dilutional anemia (hemoglobin 10.810.8 g/dL) and a chronic respiratory alkalosis (pH 7.447.44, low pCO₂, low HCO₃⁻).
During pregnancy, progesterone stimulates the respiratory center, leading to increased minute ventilation and chronic respiratory alkalosis with metabolic compensation.
3
Assess for signs of a systemic lupus erythematosus flare.
The platelet count is normal, serum creatinine is normal, and urinalysis lacks cellular casts or significant proteinuria.
Lupus nephritis or a systemic flare would typically present with active urine sediment, worsening kidney function, hypertension, or severe cytopenias.
4
Determine the most appropriate management.
Because all findings are consistent with normal physiologic changes of pregnancy and there is no evidence of a lupus flare, reassurance is indicated.
Unnecessary medical interventions can cause harm to both the mother and the fetus.

Key Concept

Recognizing the normal physiologic changes of pregnancy (e.g., dilutional anemia, chronic respiratory alkalosis, trace edema) in a patient with systemic lupus erythematosus to avoid misdiagnosing a disease flare.
Estimated Time:1m 30s
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Topics

Rheumatology and Immunology

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