Renal Case Study Questions Learning Outcomes 1. Learn how to evaluate laboratory test results and compare to symptoms displayed by the patient. 2. Identify disturbances in plasma electrolytes and pH and compare to reference values. 3. Identify possible causes of the acidosis and alkalosis disturbances. 4. Outline the main mechanisms by which the kidney regulates plasma pH in the body. 5. Learn about calcium balance and how the kidneys deal with hyper or hypocalcemia. 6. Review drug interactions and the problem(s) associated with over the counter (OTC) medications. Knowledge and Understanding Part I Questions 1. List the symptoms being displayed by the patient. 2. Review the lab values in table 1 and 2, indicate what is the significance of each test. Create a table for ease of reviewing. 3. Do any of her laboratory results account for the symptoms of the patient. List those lab results that match her symptoms. 4. List the test results that are below or above normal values (table 1 vs. table 2) and provide the possible medical condition(s) of the patient. 5. Which of the lab values gives you information about how Mrs. Burroughs’ kidneys are functioning? 6. Why is the physician interested in Mrs. Burroughs’ kidney function? Part II Questions 1. What is the mechanism of action of hydrochlorothiazide? Review specifically what is the role of the medication. It will assist you in answering the questions in part IV. 2. Check the OTC medications and provide the mechanisms of action. Create a table for ease of grading. 3. Check drug interactions between prescribed and non-prescribe medications to help you answer the next question by reviewing the interactions (drugs.com). List the information. 4. Could any of Mrs. Burroughs’ current problems be related to the drugs (over the counter or prescription or the combination) she has been taking? Describe why do you think there is a relationship. Part III Questions 1. What is parathyroid hormone (PTH)? What gland produces it what is its physiological function? What is/are the target organ(s)? 2. Why do you think the physician wants to know about the levels of this hormone? 3. Compare the serum calcium values of Mrs. Burroughs to the reference value (range) of PTH provided on the PTH-Calcium normogram on Canvas. Describe what she may be suffering from? 4. Why do you think the doctor stated the PTH levels are within what the doctor expected (8 mg/dL)? Second paragraph on part III of the case study. 5. Review the last sentence on part III regarding the patient’s 2 main problems the doctor listed. If the doctor stated Mrs. Burroughs has too little acid what does that indicate to you? Explain your answer using physiology principles. 6. What do you think is the result of the patient drinking too much milk and what hormone would be activated to excrete any excess calcium? Describe the mechanism of action of the hormone. 7. Research the symptoms of acidosis and alkalosis (both respiratory and metabolic) and list the information. Create table to present the information. 8. Compare Mrs. Burroughs’ symptoms to the symptoms you listed in the previous question and determine what she may be suffering from? 9. Based on your knowledge of reabsorption and secretion in the nephron and acid-base balance, describe how does the renal system can resolve the acidosis or alkalosis (depending on what is your answer in the previous question). Part IV Questions 1. Review the diagram on part IV of the case study related to normal Calcium reabsorption. In addition, review your answers in section III and explain why do you think her serum calcium levels are elevated. 2. Based on you answer in question 1, part II, what is the possible problem in the reabsorption of Calcium? Use the diagram in part IV of the case study. 3. Is there a problem with Mrs. Burroughs’ breathing? What kind of change do you expect to see as respiratory compensation of a patient suffering from what you indicated is the problem in question 8 in part III? Reflection (individual answers) 1. What should we be the concern regarding over the counter medications? 2. What skill(s) did you learn (individual or group) from the case study? List all if there is more than one or different. 3. Did the case study help you in understanding how laboratory test can provide direct information on acid-base balance? Explain in detail 4. What did you learn that can help you in the future? List all if there is more than one. 5. What other information could have been provided to help you understand the case study? A Case Study in Renal Physiology and Acid-Base Balance Part I – At the Hospital “Something is wrong. My mother is sick and very disoriented,” explained Bobby, a middle-aged man, who was looking very anxious as he spoke with staff in the Emergency Department (ED) where he had brought his mother, Arlene Burroughs, an 83-year-old white woman. “She’s disoriented and lethargic, and she has been vomiting and complaining of an upset stomach,” he said to the triage nurse who examined Mrs. Burroughs. The nurse noted that Mrs. Burroughs did not have a fever or any other signs of infection but that she did appear to be dehydrated. Table 1. Grandma’s Test Results Serum creatinine = 8.3 mg / dL BUN (blood urea nitrogen) = 55mg / dL Serum calcium (total) = 15.76 mg / dL Serum sodium = 128 mEq / L Serum potassium = 2.7 mEq / L Serum bicarbonate (venous) > 40 mEq / L Serum pH (venous) = 7.67 Urinary potassium = 45 mEq / L The attending physician in the ED ordered a battery of tests. “I’m especially concerned about her kidney function,” he told Bobby. I don’t understand, said Bobby. Shouldn’t you be looking at her brain? That seems to be where the problem is! She is really confused, and doesn’t that tell you that something is wrong with her brain function? What if she’s had a stroke? “Well, she certainly may be having some problems, but her brain and nerves may be responding to changes that are produced by her kidneys,” the doctor explained. “Let’s get some more information so we’ll know where to look for the problem.” The results of these tests are provided in Table 1. Table 2 provides normal ranges of values for standard laboratory tests. Table 2: Selected Normal Laboratory Values Blood Gases pH pCO2 (mmHg) pO2 (mmHg) HCO3 (mEq/L) O2 Sat % Kidney Function Test BUN (blood urea nitrogen) Serum Creatinine Electrolytes Calcium Calcium, ionized Chloride Renal Physiology Arterial 7.35 - 7.45 35 – 45 70 – 100 19 – 25 90 – 95 Venous 7.32 - 7.42 38 – 52 28 – 48 19 – 25 40 – 70 7 – 20 mg/dL 0.5 – 1.4 mg/dL 8.8 – 10.3 mg/dL 2.24 – 2.46 mEq/L 95 – 107 mEq/L Page 1 Magnesium Phosphate Potassium Sodium 1.6 – 2.4 mEq/L 2.5 – 4.5 mEq/L 3.5 – 5.2 mEq/L 135 – 147 mEq/L Part II – What Else Do We Know About the Patient? Bobby handed the physician a paper bag with several bottles in it. “These were on Mom’s kitchen table,” he said. “I just don’t understand—she’s very good about taking her medicine.” In the bag is a bottle of hydrochlorothiazide (25mg), a prescription medicine used to lower blood pressure. The label on the bottle reads, “Take one capsule in the morning and one capsule in the evening.” “Mom calls these her ‘water pills.” She complains that they make her use the restroom more often. Also, in the bag were a bottle of Tums Ultra 1000 mg (CaCO3) and Alka-Seltzer (NaHCO3). “Do you know how often your mother takes the Alka-Seltzer?” the doctor asked Bobby. “Or how many Tums?” “Oh, I’m not sure. I can’t be with her all day, and she lives alone. We take turns checking on her, me, my daughter, and my brother’s family. But I don’t understand why you need to know about these,” replied Bobby, looking closely at the bottle of brightly colored tablets. “We buy them at the grocery store, it’s not like they’re medicine, or anything.” Just then, Mr. Burroughs’ daughter, Charlotte, entered the examination room. Charlotte was a biology major in college. “I came as fast as I could,” she added,” but traffic from school was a bear. What’s wrong with Granny?” “We were just looking at your grandmother’s medicines,” said the doctor. Your father was trying to give me some more information, so we can figure out what’s causing her problems. Do you know anything about the Alka-Seltzer or the Tums he found on her kitchen table? Charlotte looked at the physician and her dad. “Granny was taking the Alka-Seltzer this week because she was complaining about an ulcer. She said this was how they used to treat them when she was a girl. She always took it when I was there. I think she was drinking a lot of milk lately, too, and she said it was good for her stomach. And she always took the Tums because they are supposed to be good for your bones, right? I think she took those twice a day.” “Now that you mention it,” Bobby chimed in, “she took the Alka-Seltzer every time I was there too. I think she’s finished about two gallons of milk just this week, which is surprising since she usually doesn’t like milk. I always thought it was sort of funny that she didn’t like the taste of milk even though she grew up on a dairy farm.” “Hmmmm, I think we’d better see what her parathyroid hormone levels are,” the physician said. “I’ll have those measurements made right away. I’ve got a hunch that we’ll find there is more wrong with her kidneys than we thought before.” An alarm went off on his pager. “Excuse me for just a minute—I need to check on another patient before she goes home. Don’t go away and don’t worry—your mother is in excellent hands.” Part III – PTH Levels Bobby and Charlotte were with Mrs. Burroughs’ in her room. She had been admitted to the hospital and was receiving intravenous fluids. She seemed to be feeling better and was less confused. At the moment, she was sitting up in bed, chatting a bit and napping intermittently. Renal Physiology Page 2 The physician knocked at the door. “How is everyone? Mrs. Burroughs, how are you feeling? Better, thank you,” replied Mrs. Burroughs. “My stomach doesn’t seem to hurt as much. Should I take my Tums now? I don’t want to fall and break a hip! And it’s really about time for a glass of milk.” Oh, I don’t think there’s much danger of falling here. In fact, I don’t think you should be taking either the Alka- Seltzer or the Tums, since I think that’s what caused the problem, said the doctor. It looks like your serum PTH is 8mg/dL, about what I expected. This tells me that the antacids may have altered your kidney function, and that’s how you ended up in here.” So, she’s sick now because of the Tums asked Bobby, incredulously. Why do they sell those things if they make people sick? Well, I think she’s sick now because maybe she took too many Tums and the Alka-Seltzer, replied Charlotte. But I thought that the kidney would just eliminate anything that the body can’t use, if it’s water-soluble of course. I don’t understand why her body didn’t protect her from that, if it was dangerous.” Your daughter is on the right track,” said the physician. The kidney is responsible for regulating the amount of every substance in the body’s internal environment. Your mother has got two main problems: too much calcium and too little acid. Renal Physiology Page 3 Part IV – What about the Calcium? Oh, I see it now! All her symptoms are due to her kidneys not working well, so the pH and concentrations of ions were not right in her body, said Charlotte. See, the important chemical reaction is this one, she added as she wrote this on a piece of paper: CO2 + H2O ⇄ H2CO3 ⇄ H+ + HCO3This reaction shows why carbonic acid, H2CO3, works as a buffer. We are learning about this in my biochemistry class at school. It can tie up H+ ions when there are too many, or it can produce more H+ ions when there are too few. This keeps the concentration of H+ and pH relatively constant. The kidney regulates the concentration of HCO3- by preventing its loss in the kidney tubules. It can also secrete HCO3- into the kidney tubule when there is too much in the body. It also shows how the lungs and the kidneys work together to regulate pH in the body, said the physician. CO2 is a gas, remember? The lungs, well really the brain and nervous system, can change the amount of CO2 present in the body by changing respiratory rate. Alright, I understand about the pH being too high. Granny would not have developed this if she had not taken all those antacid tablets. But I don’t understand why her calcium levels are so high? And, she had osteoporosis—shouldn’t any calcium she took be incorporated into her bones? Charlotte asked. Wait a minute, I’m not understanding. Is there a problem with her breathing now? exclaimed Bobby. Well, regulation of calcium also involves some kidney mechanisms, the physician replied, holding up a hand to deflect Bobby’s question for a minute. Let me draw a diagram that shows how calcium is reabsorbed from the kidney, specifically the distal convoluted tubule, you might be able to see some of the other things that can alter it. PTH also works here to stimulate calcium reabsorption from the kidney tubule, in addition to promoting its absorption from the digestive tract. The physician drew the diagram on a piece of paper. This represents the distal convoluted tubule, or DCT, which is ‘downstream,’ or distal to the PCT in the nephron. I’m only showing some of the pertinent calcium pathways here, but you should know that kidney function is complex. We’re learning more about it all the time.” Figure 2. Distal convoluted tubule (DCT). Adapted from: Ives, H.E. (2012) Diuretic Agents. In B.G. Katzung, S.B. Masters, and A.J. Trevor (eds.) Basic and Clinical Pharmacology (p. 254). New York: McGraw-Hill. Purple pump: Na/K pump; Blue pump: Ca-Na pump Red pump: Ca-H pump Green pump: Na-Cl pump Renal Physiology Page 4 Here, you should be able to see that reabsorption of calcium is very dependent on sodium movement across the cell membranes. So, anything that changes the movement of sodium across a cell membrane would also be expected to change the movement of calcium. Just as an example—your grandmother is taking a thiazide diuretic. These medications work right here, in the DCT, to inhibit the reabsorption of sodium and chloride from the tubular fluid. You should be able to see how they can promote both hypercalcemia and alkalosis in someone like her. And, no, there’s not a problem with her breathing. Although the respiratory system can respond quickly, it can’t completely overcome the problems in her kidneys. Renal Physiology Page 5
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