Case 1

A 65-year-old man has congestive heart failure. He is seen by his physician because he has run out of his medications. He presents with easy fatigability, shortness of breath, and swelling of his ankles. On physical examination he is found to have distended neck veins and pitting edema of the ankles. His breathing is rapid (20 breaths/min), and rales (i.e., fluid in the lungs) are heard bilaterally at the bases of the lungs. He is afebrile, with a pulse rate of 110 beats/min and a blood pressure of 110/70 mm Hg. A blood sample is obtained, and the following abnormalities are noted:

• 
  

  Serum [Na ⁺ ] = 130 mEq/L

  
  
• 
  

  Serum [K ⁺ ] = 3.0 mEq/L

  
  
• 
  

  Serum [creatinine] = 1.4 mg/dL

Questions

• 1a.
  

  Is the extracellular fluid (ECF) volume in this man increased or decreased from normal? What evidence in the physical examination supports your conclusion?

  
  
• 1b.
  

  Is the effective circulating volume (ECV) in this man increased or decreased from normal?

  
  
• 1c.
  

  What would you predict to be the levels (activities) of atrial natriuretic peptide, brain natriuretic peptide, arginine vasopressin, and renin-angiotensin-aldosterone and the functioning of the sympathetic nervous system in this man, and why?

  
  
• 1d.
  

  How would you characterize renal Na ⁺ handling in this man? What evidence in the physical examination supports this conclusion?

  
  
• 1e.
  

  What is the mechanism for the development of hyponatremia in this man?

  
  
• 1f.
  

  What is the mechanism for the development of hypokalemia in this man?

  
  
• 1g.
  

  The physician treating this man prescribes a loop diuretic to reduce Na ⁺ retention and reduce his edema. It is known that patients with congestive heart failure do not respond as well to loop diuretics as healthy patients would (i.e., the degree of natriuresis is less). What explains the decreased effect of the loop diuretic in a patient with congestive heart failure?

  
  
• 1h.
  

  What effect will the loop diuretic have on this man’s ECF volume and ECV?

  
  
• 1i.
  

  While he is taking the loop diuretic, the serum [K ⁺ ] of this man decreases from 3.0 to 2.5 mEq/L. What is the mechanism for this diuretic-induced hypokalemia?

  
  
• 1j.
  

  After administration of the diuretic, the serum [creatinine] increases from 1.4 to 1.8 mg/dL. Why was the serum [creatinine] elevated, and why did it increase further after treatment with the loop diuretic?

Case 2

A 49-year-old woman sees her physician because of weakness, easy fatigability, and loss of appetite. During the past month she has lost 7 kg (15 lb). On physical examination she is found to have hyperpigmentation, especially of the oral mucosa and gums. She is hypotensive, and her blood pressure (BP) falls when she assumes an upright posture (BP = 100/60 mm Hg supine and 80/50 mm Hg erect). The following laboratory data are obtained:

• 
  

  Serum [Na ⁺ ] = 132 mEq/L

  
  
• 
  

  Serum [K ⁺ ] = 6.5 mEq/L

  
  
• 
  

  Serum [ <SPAN role=presentation tabIndex=0 id=MathJax-Element-1-Frame class=MathJax style="POSITION: relative" data-mathml='HCO3−’>HCO−3HCO3−
  HCO 3 −
  ] = 20 mEq/L

  
  
• 
  

  Urine [Na ⁺ ] = 20 mEq/L

Questions

• 2a.
  

  The plasma level of what hormone(s) would be expected to be below normal in this woman?

  
  
• 2b.
  

  How do you explain the urine [Na ⁺ ] of 20 mEq/L in this woman? What would you expect the urine [Na ⁺ ] to be in an individual who is volume depleted? What relationship does this have to the hypotension in this woman?

  
  
• 2c.
  

  What is the mechanism for development of hyponatremia in this woman?

  
  
• 2d.
  

  Why does this woman have hyperkalemia?

  
  
• 2e.
  

  What is the acid-base disturbance in this woman, and what is its cause?

Case 3

A 70-year-old man with lung cancer develops the syndrome of inappropriate antidiuresis (SIAD). He is admitted to the hospital, and the following data are obtained. His vital signs are normal, as is the physical examination. There is no evidence of ECF volume contraction or ECF volume expansion.

• 
  

  Body weight = 70 kg

  
  
• 
  

  Serum [Na ⁺ ] = 120 mEq/L (normal = 135 to 147 mEq/L)

  
  
• 
  

  Urine osmolality = 600 mOsm/kg H ₂ O

  
  
• 
  

  Urine [Na ⁺ ] excretion = 80 mEq/day