A 65-year-old man comes to the hospital with a 1-day history of increasing shortness of breath and cough. He has been using albuterol occasionally without relief of symptoms. The patient is noncompliant with medications and has not seen a doctor in the past year. He smoked 1 pack of cigarettes daily for 40 years. Temperature is 37.5 C (99.5 F), blood pressure is 110/70 mm Hg, pulse is 98/min, and respirations are 20/min. His pulse oximetry shows 86% on room air. Examination shows jugular venous distension, and lung auscultation reveals diffuse wheezing with no crackles. His heart sounds are distant. Mild hepatomegaly is present, and he has bilateral pitting edema halfway to the knees. Chest x-ray reveals hyperinflated lungs and a flattened diaphragm with no infiltrates. He is started on systemic steroids, bronchodilator nebulization, and furosemide. Laboratory studies at the time of admission and 5 days later show the following: Which of the following is the most likely explanation for the changes in acid-base balance and serum chemistry values between day 1 and day 5 in this patient?

Question

A 65-year-old man comes to the hospital with a 1-day history of increasing shortness of breath and cough.  He has been using albuterol occasionally without relief of symptoms.  The patient is noncompliant with medications and has not seen a doctor in the past year.  He smoked 1 pack of cigarettes daily for 40 years.  Temperature is 37.5 C (99.5 F), blood pressure is 110/70 mm Hg, pulse is 98/min, and respirations are 20/min.  His pulse oximetry shows 86% on room air.  Examination shows jugular venous distension, and lung auscultation reveals diffuse wheezing with no crackles.  His heart sounds are distant.  Mild hepatomegaly is present, and he has bilateral pitting edema halfway to the knees.  Chest x-ray reveals hyperinflated lungs and a flattened diaphragm with no infiltrates.  He is started on systemic steroids, bronchodilator nebulization, and furosemide.  Laboratory studies at the time of admission and 5 days later show the following:  Which of the following is the most likely explanation for the changes in acid-base balance and serum chemistry values between day 1 and day 5 in this patient?

Quizplus · Accepted Answer

Explanation: This patient with an extensive smoking history has a chronic obstructive pulmonary disease (COPD) exacerbation (dyspnea, cough, wheezing, hypoxia), which was treated with glucocorticoids and bronchodilators. In addition, his elevated jugular venous pressure, hepatomegaly, and peripheral edema in the presence of clear lungs suggest pulmonary hypertension and cor pulmonale, likely due to COPD. In cor pulmonale, loop diuretics (eg, furosemide) are often used to lower right ventricular filling volumes and reduce peripheral edema. However, they can lead to hypovolemia, low cardiac output, and renal hypoperfusion. Prerenal azotemia/acute kidney injury (AKI) can develop, as reflected by this patient's laboratory values on the fifth day of hospitalization: Elevated creatinine (doubled from admission) Elevated blood urea nitrogen (BUN) with BUN:creatinine ratio >20 Elevated anion gap metabolic acidosis [(Na) - (Cl + HCO₃) = 139 - (98 + 23) = 18] likely from uremia Although diuretic use can cause hypokalemia, AKI negates that effect, explaining this patient's stable potassium levels. The other laboratory values are related to his underlying COPD. At baseline, patients with COPD have chronic respiratory acidosis (high PaCO₂ from CO₂ retention) with compensatory (renal) metabolic alkalosis (high bicarbonate) and a near normal pH. In COPD exacerbation, there is an acute rise in PaCO₂ (acute-on-chronic respiratory acidosis) with a low pH, as seen on admission of this patient. With appropriate treatment, these values should return to their baseline. However, despite having a lowered PaCO₂ (likely close to his baseline), this patient continues to have low pH and a serum bicarbonate level below what would be expected in chronic COPD. This suggests development of metabolic acidosis due to renal failure and uremia. ₂ ₂ ₂ ₂ (Choices B and C) Diabetic ketoacidosis is typically accompanied by much higher glucose levels (eg, >400 mg/dL). Glucocorticoids can increase serum BUN due to their catabolic effect on body proteins and can cause hyperglycemia; however, they are unlikely to cause creatinine elevation. (Choices D and E) Obstructive sleep apnea can lead to chronic respiratory acidosis with compensatory metabolic alkalosis but would not cause acute metabolic acidosis. Worsening respiratory failure would lead to an increase (not a decrease) in PaCO₂. ₂ Educational objective: Patients with chronic obstructive pulmonary disease often have chronic CO₂ retention, resulting in respiratory acidosis and compensatory metabolic alkalosis. Diuretics are often administered to treat cor pulmonale symptoms but must be used cautiously as they can lead to a reduction in cardiac output and subsequent development of prerenal acute renal injury. ₂

A 65-Year-Old Man Comes to the Hospital with a 1-Day