22

22 CASE 22


A 70-year-old woman admitted 3 days earlier to the cardiac care unit after angioplasty has gone into renal failure.


The patient arrived in the emergency department complaining of chest pain and was diagnosed with an ongoing myocardial infarction. Imaging revealed a stenosis of three major coronary arteries, and the patient was immediately transferred to surgery for angioplasty. Subsequent imaging indicates that one of the three vessels is again stenosing, and the patient’s progress is being monitored through serial radiologic imaging.


The patient was diagnosed 5 years ago with non–insulin-dependent diabetes mellitus (type 2), which has been managed with diet and exercise.



PHYSICAL EXAMINATION



VS: T 37°C, P 80/min, R 22/min, BP 100/70 mm Hg

PE: Incision scars on both legs, from the percutaneous angioplasty, are healing. No other notable findings.


LABORATORY STUDIES



Plasma analysis: Elevations in blood urea nitrogen and creatinine, increasing progressively with each daily measurement and reaching 50% above normal by day 3.

Urinalysis: Muddy brown epithelial cell casts and debris. Urine production is 300 mL/day (oliguria). Fractional excretion of sodium is 3%, and urine osmolarity is 200 mOsm/kg.


DIAGNOSIS


Acute tubular necrosis



PATHOPHYSIOLOGY OF KEY SYMPTOMS


Iodinated contrast media is toxic to renal tubular cells. In patients with underlying risk factors such as diabetes, or age and heart failure, contrast media containing more than 100 g of iodide will induce acute tubular necrosis.


The renal tubules are composed of epithelial cells, with the apical surface facing the lumen of the tubule. Tubular segments, particularly the proximal tubule and the thick ascending limb of the loop of Henle, have numerous mitochondria and are metabolically active. Transport proteins on both the apical and basolateral surfaces facilitate the selective reabsorption of nutrients and electrolytes across the tubular epithelium (Figs. 22-1 and 22-2).


image

FIGURE 22–1 Cellular ultrastructure and primary transport characteristics of the proximal tubule. The proximal tubules reabsorb about 65% of the filtered sodium, chloride, bicarbonate, and potassium and essentially all the filtered glucose and amino acids. The proximal tubules also secrete organic acids, bases, and hydrogen ions into the tubular lumen.


image

FIGURE 22–2 Cellular ultrastructure and transport characteristics of the thin descending loop of Henle (top) and the thick ascending segment of the loop of Henle (bottom). The descending part of the thin segment of the loop of Henle is highly permeable to water and moderately permeable to most solutes but has few mitochondria and little or no active reabsorption. The thick ascending limb of the loop of Henle reabsorbs about 25% of the filtered loads of sodium, chloride, and potassium, as well as large amounts of calcium, bicarbonate, and magnesium. This segment also secretes hydrogen ions into the tubular lumen.

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Jul 4, 2016 | Posted by in PHYSIOLOGY | Comments Off on 22

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