CHAPTER 22 Renal Disorders 537
sufficiently high blood pressure is necessary for kidney function because glomerular filtration requires high hydrostatic pressure. Large blood loss from the body, as in hemorrhage, is a common cause of prerenal kidney injury caused by ischemia. Intrarenal Dysfunction Direct damage to renal tissue, as in trauma or toxic injury, causes nephron damage within the kidney itself, known as intrarenal dysfunction. This is most commonly caused by nephrotoxic medications, renal infections, or systemic illnesses that affect the kidney. Common examples include nephrotoxicity caused by NSAIDs and poststreptococcal glomerulonephritis (PSGN). Both of these conditions cause direct injury to the kidney. Autoimmune diseases, untreated HTN, and uncontrolled DM also directly harm the kidney caus- ing intrarenal dysfunction. Postrenal Dysfunction Postrenal dysfunction is caused by obstructive urop- athy, a problem that prevents urine outflow from the kidney. Conditions that can cause obstruction include kidney stones in the ureter, prostate gland enlargement, and bladder cancer. In postrenal kidney dysfunction, urine backs up within the ureter and into the kidney, which can lead to hydronephrosis , a fluid-filled, swol- len kidney. Urine is toxic to the nephron cells, and urine stagnation increases the risk of infection. Acute Tubular Necrosis Ischemia and hypoxia can damage the renal tubules and result in acute tubular necrosis (ATN) , the most com- mon cause of acute kidney injury (AKI) . With ischemia, cells of the nephron tubules slough into the tubular lumen. The lumen becomes blocked, preventing fluid from flowing through them, thereby reducing urine for- mation. The blocked lumen further contributes to isch- emic injury to cells lining the tubules, causing additional intrarenal injury. Unless this process is reversed, renal failure with permanent injury to the kidney will occur. Assessment The history and physical assessment for patients with renal disease includes determining exposure to any medications or nephrotoxic substances. Additionally, any systemic illnesses or infections associated with renal damage need to be identified. Illnesses such as HTN and DM are important causes of renal damage. Patients need to be asked about their pattern of urine excretion and the character of their urine. Typi- cal questions would include the following: • Does the urine have an unusual odor or color? • Is the urine foamy?
• Is the urine very dark or tea-colored? • Is there blood in the urine? • Is there pain or burning on urination? Is there abdominal or flank pain on urination? • Have you noticed any change in the amount of urine or the frequency of urination? Risk Factors Exposure to nephrotoxic agents is one of the great- est risks for the development of renal disorders. A list of current medications is needed, as many drug metabolites are particularly nephrotoxic. Specific questions concerning HTN and DM are important. The patient needs to describe the duration of the disorder, medications involved, and management of the disorders.
ALERT! Long-term DM and HTN often lead to renal failure.
The patient should be asked about a recent strep- tococcal infection because poststreptococcal glomer- ulonephritis (PSGN) can occur. Patients who have had major surgery are at risk for altered renal function, as major surgery can reduce renal blood flow and lead to kidney injury. A reduction in renal blood flow is also a concern for patients who have had an acute myo- cardial infarction or heart failure. Renal ischemia is a common complication of severe heart failure. Signs and Symptoms The patient with renal failure generally has a vari- ety of multisystemic symptoms, which are the result of reduced secretory and excretory functions of the kidney. The symptoms can include fatigue, weakness, nausea, constipation, abdominal pain, and confusion. Patients with renal calculi may have abdominal or flank pain in addition to hematuria. Costovertebral angle (CVA) tenderness is a classic sign of a kidney disorder, particularly infection (see Fig. 22-4). The presence of blood ( hematuria ) or protein ( proteinuria ) in urine is often readily apparent to the patient. Urine looks pink or red when blood is present and foamy when it contains high levels of protein. Tea-colored urine often indicates bilirubin is in the urine, as occurs in jaundice. All these signs are an indication for further study.
CLINICAL CONCEPT Hematuria is most often a sign of renal calculi or an infection.
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