Upper Urinary Tract Infection: Acute Pyelonephritis

UPPER URINARY TRACT INFECTION:ACUTE PYELONEPHRITIS

Pyelonephritis is a bacterial infection of the renal pelvis, tubules, and interstitial tissue of one or both kidneys. Upper UTIs are as-sociated with the antibody coating of the bacteria in the urine. (This occurs in the renal medulla; when the bacteria are excreted in the urine, the immunofluorescent test can detect the antibody coating.) Bacteria reach the bladder by means of the urethra and ascend to the kidney. Although the kidneys receive 20% to 25% of the cardiac output, bacteria rarely reach the kidneys from the blood: fewer than 3% of cases are due to hematogenous spread (Warren et al., 1999).

Pyelonephritis is frequently secondary to ureterovesical reflux, in which an incompetent ureterovesical valve allows the urine to back up (reflux) into the ureters (see Fig. 45-1). Urinary tract ob-struction (which increases the susceptibility of the kidneys to in-fection), bladder tumors, strictures, benign prostatic hyperplasia, and urinary stones are some of the other causes. Pyelonephritis may be acute or chronic.

Patients with acute pyelonephritis usually have enlarged kid-neys with interstitial infiltrations of inflammatory cells. Abscesses may be noted on the renal capsule and at the corticomedullary junction. Eventually, atrophy and destruction of tubules and the glomeruli may result. When pyelonephritis becomes chronic, the kidneys become scarred, contracted, and nonfunctioning.

Clinical Manifestations

The patient with acute pyelonephritis appears acutely ill with chills and fever, leukocytosis, bacteriuria and pyuria, flank pain, and CVA tenderness. In addition, symptoms of lower urinary tract involvement, such as dysuria and frequency, are common.

Assessment and Diagnostic Findings

An ultrasound study or a CT scan may be performed to locate any obstruction in the urinary tract. Relief of obstruction is essential to save the kidney from destruction. An IVP is rarely indicated during acute pyelonephritis because findings are normal in up to 75% of patients. Radionuclide imaging with gallium citrate and indium-111 (In¹¹¹)–labeled WBCs may be useful to identify sites of infection that may not be visualized on CT scan or ultrasound. Urine culture and sensitivity tests are performed to determine the causative organism so that appropriate antimicrobial agents can be prescribed.

Medical Management

Patients with acute uncomplicated pyelonephritis are usually treated as outpatients if they are not dehydrated, not experi-encing nausea or vomiting, and not showing signs or symptoms of sepsis. In addition, they must be responsible and reliable to ensure that all medications are taken as prescribed. Other pa-tients, including all pregnant women, may be hospitalized for at least 2 or 3 days of parenteral therapy. Oral agents may be substituted once the patient is afebrile and showing clinical improvement.

PHARMACOLOGIC THERAPY

For outpatients, a 2-week course of antibiotics is recommended because renal parenchymal disease is more difficult to eradicate than mucosal bladder infections. Commonly prescribed agents include TMP-SMZ, ciprofloxacin, gentamicin with or without ampicillin, or a third-generation cephalosporin (Warren et al., 1999). These medications must be used with great caution if the patient has renal or liver dysfunction.

A possible problem in acute pyelonephritis treatment is a chronic or recurring symptomless infection persisting for months or years. After the initial antibiotic regimen, the patient may need antibiotic therapy for up to 6 weeks if evidence of a relapse is seen. A follow-up urine culture is done 2 weeks after completion of anti-biotic therapy to document clearing of the infection.