Porth's Essentials of Pathophysiology, 4e

203

Disorders of Fluid, Electrolyte, and Acid–Base Balance

C h a p t e r 8

R E V I EW E X E R C I S E S

A. Explain her low K + and Cl – . B. What type of acid–base abnormality would you expect her to have? 6. A 65-year-old man with chronic obstructive lung disease has been using low-flow oxygen therapy. He has recently developed a severe respiratory tract infection and has trouble breathing. He is admitted to the emergency room because his wife is having trouble arousing him. She relates that he had “turned his oxygen way up” because of difficulty breathing. His respirations are 12 breaths/minute. Arterial blood gases, drawn on admission to the emergency room, indicated a PO 2 of 85 mm Hg (normal, 90 to 95 mmHg) and a PCO 2 of 90 mm Hg (normal, 40 mm Hg). His serum HCO 3 – was 34 mEq/L (normal, 24 to 48 mEq/L). What is his pH? A. What is the most likely cause of this man’s problem? B. How would you explain the lethargy and difficulty in arousal? C. What would be the main goal of treatment for this man in terms of acid–base balance? D. Explain the concurrent respiratory and metabolic acidosis that often occurs in persons with chronic respiratory acidosis. 1. Rhoades RA, Bell DR. Medical Physiology . 4th ed. Philadelphia, PA: Wolter Kluwer Health | Lippincott Williams & Wilkins; 2013:20–33, 427–470, 282–287, 451–470. 2. Hall JE. Guyton and Hall Textbook of Medical Physiology . 12th ed. Philadelphia, PA: Saunders Elsevier; 2011:285–301, 177–189, 870–871, 355–360, 379–396, 955–967. 3. Metheney NM. Fluid and Electrolyte Balance . 5th ed. Sudbury, MA: Jones & Bartlett; 2012:3–12, 41–44, 45–67, 69–90, 91–109, 112–122, 123–126, 137–153. 4. Rose BD, Post TW. Clinical Physiology of Acid–base and Electrolyte Disorders . 5th ed. New York: McGraw-Hill; 2001:187–190, 478–479, 547, 682–692, 823–842, 896–897. 5. Demling RH. The burn edema process: Current concepts. J Burn Care Rehabil. 2005;26:207–227. 6. O’Brien JG, Chennubhotla RV. Treatment of edema. Am Fam Physician. 2005;71(11):2111–2117. 7. Koeppen BM, Stanton BA. Berne & Levy Physiology . 6th ed. Philadelphia, PA: Mosby Elsevier; 2010:346–353, 594–663, 699–705, 636–650. 8. Porth CM, Erickson M. Physiology of thirst and drinking. Heart Lung. 1992;21:273–284. 9. McKinley MJ, Johnson AK. The physiological regulation of thirst and fluid intake. News Physiol Sci. 2004;19:1–6. 10. Hodak SP, Verbalis JO. Abnormalities in water homeostasis in aging. Endocrinol Metab Clin North Am. 2005;34:1031–1046. 11. Dundas B, Harris M, Narasimhan M. Psychogenic polydipsia. Curr Psychiatry Rep. 2007;9(3):236–241. 12. Siegel AJ. Hyponatremia in psychiatric patients: Update on evaluation and management. Harv Rev Psychiatry. 2008;16(1):13–24. R E F E R E N C E S

1. A 40-year-old man with advanced acquired immunodeficiency syndrome (AIDS) presents with an acute chest infection. Investigations confirm a diagnosis of Pneumocystis carinii pneumonia. Although he is being treated appropriately, his serum sodium level is 118 mEq/L. Tests of adrenal function are normal. A. What is the likely cause of his electrolyte disturbance? B. What are the five cardinal features of this condition? 2. A 70-year-old woman who is taking furosemide (a loop diuretic) for congestive heart failure complains of weakness, fatigue, and cramping of the muscles in her legs. Her serum potassium is 2.0 mEq/L and her serum sodium is 140 mEq/L. She also complains that she notices a “strange heartbeat” at times. A. What is the likely cause of this woman’s symptoms? B. An ECG shows a depressed ST segment and low T-wave changes. Explain the physiologic mechanism underlying these changes. C. What would be the treatment for this woman? 3. A 50-year-old woman presents with symptomatic hypercalcemia. She has a recent history of breast cancer treatment. A. How do you evaluate this person with increased serum calcium levels? B. What is the significance of the recent history of malignancy? C. What further tests may be indicated? 4. A 34-year-old woman with diabetes is admitted to the emergency room in a stuporous state. Her skin is flushed and warm, her breath has a sweet odor, her pulse is rapid and weak, and her respirations are rapid and deep. Her initial laboratory tests indicate a blood sugar of 320 mg/dL, serum HCO 3 – of 12 mEq/L (normal, 24 to 27 mEq/L), and a pH of 7.1 (normal, 7.35 to 7.45). A. What is the most likely cause of her lowered pH and bicarbonate levels? B. How would you account for her rapid and deep respirations? C. How would you explain her warm, flushed skin and stuporous mental state? 5. A 16-year-old girl is seen by her primary care provider because her parents are concerned about her binge eating and their recent discovery that she engages in self-induced vomiting. Initial laboratory tests reveal a serum K + of 3.0 mEq/L and Cl – of 93.