Critical Care Medicine-Renal, Electrolyte and Acid Base Disorders>>>>>Acid Base Disorders
Question 6#

A 62-year-old man with past medical history of benign prostate hyperplasia, congestive heart failure, and hyperlipidemia presents to his primary care physician for a routine follow-up visit. Today, he complains of progressively worsening fatigue and back pain for the past 4 weeks. He states that there are days that he feels so tired that he does not leave the house. He no longer enjoys playing golf or fishing on the weekends. On physical examination, his temperature is 37.2°C, blood pressure is 134/72 mm Hg, pulse rate is 74 beats/min, and respiratory rate is 12 breaths/min. Pallor conjunctiva and point tenderness are noted over his lumbar spine. The rest of the physical examination is unremarkable. His medications include pravastatin, furosemide, and tamsulosin. He also has been taking aspirin daily for his back pain. Laboratory data show the following:

• Sodium 133 mEq/L (mmol/L)
• Potassium 3.4 mEq/L (mmol/L)
• Chloride 104 mEq/L (mmol/L)
• Bicarbonate 16 mEq/L (mmol/L)
• Glucose 243 mg/dL
• BUN 28 mg/dL
• Creatinine 1.7 mg/dL
• Albumin 2.9 g/L
• Calcium 11.3 mg/dL
• Phosphorous 3.0 mg/dL
• Total protein 6.2 g/dL
• WBC 8200/µL
• Hemoglobin 8.9 g/dL
• Hematocrit 27.3 g/dL
• Platelets 250,000/µ

ABG:

• pH 7.42
• pCO₂ 38 mm Hg

What is the MOST likely cause for the patient’s acid-base disturbance?

A. Starvation ketoacidosis
B. d-lactic acidosis
C. Normal anion gap metabolic acidosis
D. High anion gap metabolic acidosis
E. Dehydration

Correct Answer is D

Comment:

Correct Answer: D

Based on the patient’s symptoms of fatigue and back pain, along with laboratory studies, including anemia and hypoalbuminemia, the patient most likely has multiple myeloma (MM). Patients with MM also commonly have hypoalbuminemia for which a correction factor needs to be applied. For any 1 g/L decrease of albumin, the anion gap increases by 2.5. So, while the anion gap without albumin is normal at 11, after correction factor for albumin, the anion gap is >12.

Corrected anion gap (AG) = AG + 2.5 × (4.5 − measured albumin [g/dL]) When calculating the anion gap, attention should be paid to patients with hypoalbuminemia and hypophosphatemia as this will increase the anion gap further. 

References:

1. Zampieri FG, Park M, Ranzani OT, et al. Anion gap corrected for albumin, phosphate, and lactate is a good predictor of strong ion gap in critically ill patients: a nested cohort study. Rev Bras Ter Intensiva. 2013;25(3):205-211.
2. Lee S, Kang KP, Kang SK. Clinical usefulness of the serum anion gap. Electrolyte Blood Press. 2006;4:44-46.